Chapter 3 – Heredity And Common Genetic Diseases | Life Science Solution Class 10

1. Mendel
2. Muller
3. Bateson
4. Morgan.

1. Only a single plant is involved for the experiment
2. A single pair of contrasting characters is considered for the genetic results 
3. A hybrid is crossed to a homozygous
4. None of the above.

1. Pea plant 
2. Gram plant 
3. Papaya plant 
4. Mango plant.

1. 5 pairs 
2. 7 pairs 
3. 3 pairs 
4. 12 pairs.

1. 3 : 1 
2. 9 : 3 : 3 : 1 
3. 2 : 1 : 1 : 1 
4. 3 : 2 : 1.

1. Segregation 
2. Independent assortment 
3. Dominance 
4. Incomplete dominance.

Question

1. ___ includes characteristics or traits which are transmitted from one generation to another generation.
2. Full name of Mendel is ___ ___ ___.
3. Mendel’s work was published in ___. Contrasting characters which appear in F_₁ generation is called character.
4. ___ carrier and vector or transmitter or determiner of heredity.
5. Mendel experimented on ___ plant.
6. In higher and developed organism chromosome is present in ___.
7. Among two characters which do not appear in F_₁ generation is called _____ character.
8. Among two contrasting characters which do not appear in F_₁ generation is called ____.
9. 3 : 1 is the phenotypic ratio of ___.
10. 9 : 3 : 3 : 1 is the phenotypic ratio of ___.
11. Crossing of two individuals with different genotypes belonging to similar or dissimilar species is called ___.
12. Mendelian laws, ideas and his viewpoints related to heredity are collectively known as ___.
13. The external appearance of the individual or visible character of an organism is called ___.
14. ____ grains from the another to stigma of the same flower or another flower of the same plant.
15. Mendel worked with ___ pairs of contrasting characters.
16. The genetic materials that an organism inherited from parents is called ___.
17. An individual has similar gene as that of his parents or has two identical genes of same nature affecting a trait is called ___.
18. ____ coined the term genetics.
19. From the experiment of Monohybrid cross Mendel states the law of ___.
20. From the experiment of dihybrid cross Mendel states the law of ___.
21. ____ is a type of well-developed hybrid types of fowl.
22. ___ is a well-developed hybrid type of cow.
23. High yielding disease resistant wheat is ____
24. ____ is a high yielding hybrid paddy plant.
25. Parmanent change in hereditary materials (genes) and appearance of new character is known as ___.
26. The scientific name of pea plant is Pisum ___.
27. The human species has ___ pairs of chromosomes.
28. Mendel’s laws were rediscovered by Hugode Vries, Correns and ____.
29. Mendel published his research under the title of Experiment in plant ___.
30. The study of heredity is called ___.
31. Phenotype refers to the ___ organism which is genetically controlled.
32. Mendel’s work was published in ___.
33. Number of pairs of characters on which Mendel worked ___.
34. The monohybrid ratio is ___.
35. Mendel published his law in the year characteristic of an ___. 
36. True breeding plant called ___.
37. The sex determining chromosome is called ___.
38. Improved variety of paddy is ___.
39. The phenotypic ratio of monohybrid cross in F_₁ generation is ___.
40. Two identical genes affecting a trait is known as ____.

Answer

1. Heredity
2. Gregor Johann Mendel
3. 1866, One
4. Gene
5. Pea
6. Nucleus
7. Recessive
8. Dormant
9. Monohybrid cross
10. Dihybrid cross
11. Hybridization
12. Mendelism
13. Phenotype
14. Pollination
15. Seven
16. Genes
17. Homozygous
18. William Bateson
19. Segregation
20. Independent assortment
21. Hybrid
22. Hybrid Cow
23. Sonalika
24. Hybrid rice
25. Mutation
26. Sativum
27. 23
28. Tschermak
29. Physiology
30. Genetics
31. Observable
32. 1866
33. One
34. 3:1
35. 1865
36. True breed
37. Sex chromosome
38. IR-8
39. 3:1
40. Homozygous

Very Short Answer (VSA) type questions

Question 1

Who is called the father of genetics? Or, Write the full name of Father of Genetics. 

Answer

Gregor Mendel.

Question 2

Answer

Mendel’s experiments, analysis, and laws are collectively called Mendelian genetics.

Question 3

What is the name of the process by which characteristics or traits are transmitted from one generation to another generation ?

Answer

The process by which characteristics or traits are transmitted from one generation to another generation is called inheritance.

Question 4

Who coined the term Genetics? 

Answer

The term “genetics” was coined by William Bateson.

Question 5

Give example of a self-fertilized plant. 

Question 6

What do you mean by monohybrid cross? 

Answer

A monohybrid cross is a genetic cross between two individuals that differ in only one trait or gene of interest.

Question 7

Mendel’s work was first published in which journal ? 

Answer

Mendel’s work was first published in the journal Brünn Natural History Society Proceedings in 1866.

Question 8

Who rediscovered the Mendel’s works?

Answer

Mendel’s work was rediscovered independently by three scientists, namely Hugo de Vries, Carl Correns, and Erich von Tschermak, in the year 1900.

Question 9

What is the cross known as when we cross on the basis of one pair of contrasting characters? 

Answer

When we cross on the basis of one pair of contrasting characters, it is known as a monohybrid cross.

Question 10

Which cross contains 3 : 1 phenotypic ratio? 

Answer

Monohybrid cross

Question 11

On which living material Mendel did his experiment ?

Answer

Mendel performed his experiments on the garden pea plant, scientifically known as Pisum sativum.

Question 12

What is the result of Mendel’s monohybrid cross? 

Answer

A monohybrid cross results in a phenotypic ratio of 3:1, and a genotypic ratio of 1:2:1.

Question 13

What is the result of Mendel’s dihybrid cross?

Answer

The result of Mendel’s dihybrid cross is the formation of the first filial generation (F1) that displays only the dominant traits of both the genes, followed by the formation of the second filial generation (F2) that displays a phenotypic ratio of 9:3:3:1.

Question 14

How many pairs of contrasting characters Mendel took for his experiment? 

Answer

Mendel took only one pair of contrasting characters, namely round versus wrinkled seeds, for his initial experiments.

Question 15

What is the name of the character which is expressed or appears in F_₁ generation ?

Answer

The character that is expressed or appears in the F1 generation is the dominant character or trait.

Question 16

What is the name of the character which is not expressed or does not appear in F_₁ generation? 

Answer

The character that is not expressed or does not appear in the F1 generation is the recessive character or trait.

Question 17

If we cross between two hybrid tall plants then what will be the phenotypic ratio of plants that we get in F_₁ generation?

Answer

The phenotypic ratio of plants will be 3:1, where 3/4 of the offspring will be tall and 1/4 of the offspring will be dwarf.

Question 18

What type of plants are obtained in F_₁ generation if a pure tall plant is crossed with a pure dwarf plant?

Answer

If a pure tall plant (TT) is crossed with a pure dwarf plant (tt), then all the plants in the F1 generation will be tall (Tt).

Question 19

What does ‘TT’ denote in Mendel’s pea plant experiment ?

Answer

In Mendel’s pea plant experiment, TT denotes a homozygous dominant genotype.

Question 20

What does ‘Tt’ denote in Mendel’s pea plant experiment ?

Answer

In Mendel’s pea plant experiment, Tt denotes a heterozygous genotype.

Question 21

What is the condition called, when parental genes are similar to that of the offsprings? 

Answer

The condition is called homozygosity or a homozygous condition.

Question 22

What is the condition called when parental genes are dissimilar to that of the offsprings ?

Answer

The condition is called heterozygosity or a heterozygous condition.

Question 23

What is the name of the character which has external manifestation in an individual or which is visual?

Answer

The name of the character which has external manifestation in an individual or which is visible is called a phenotype.

Question 24

What is the term given to genetic characters which an organism obtains from its parents?

Answer

The term given to genetic characters which an organism obtains from its parents is called genotype.

Question 25

Cite an example of a dominant character in human beings. 

Answer

One example of a dominant character in human beings is the ability to roll the tongue, which is controlled by a dominant gene.

Question 26

Cite an example of a recessive character in human beings. 

Answer

One example of a recessive character in human beings is blue eye color, which is controlled by a recessive gene.

Question 27

Answer

The organisms selected for hybridization are called parental or P generation organisms.

Question 28

What is the name given to organisms which are produced as a result of hybridization? 

Answer

The organisms produced as a result of hybridization are called F1 or first filial generation organisms.

Question 29

What term is given to contrasting pairs of different characters having the same locus in the homologous chromosomes? 

Answer

The term given to contrasting pairs of different characters having the same locus in the homologous chromosomes is called an allelic pair or allelic gene.

Question 30

Name 2 high yielding disease resistant paddy plants that are produced by the hybridization process. 

Answer

Question 31

Name 2 high yielding wheat plants which are produced by the hybridization process.

Answer

Two high-yielding wheat plants produced by the hybridization process are Sonalika and Kalyan Sona.

Question 32

Name two artificially reproduced cows that produce large quantities of milk.

Answer

Question 33

Name two high meat content and high egg-yielding fowls produced by the hybridization process. 

Answer

Two high meat content and high egg-yielding fowls produced by the hybridization process are Rhode Island Red and White Leghorn.

Question 34

What do you mean by 3 : 1 ratio in heredity?

Answer

In heredity, a 3:1 ratio refers to the phenotypic ratio observed in the offspring of a monohybrid cross.

Question 35

 In heredity what do you mean by 1 : 2 : 1 ratio ? 

Answer

In heredity, a 1:2:1 ratio refers to the phenotypic ratio observed in the offspring of a heterozygous dihybrid cross.

Question 36

 In heredity what do you mean by  9 : 3 : 3 : 1 ratio? 

Answer

A 9:3:3:1 ratio refers to the phenotypic ratio observed in the offspring of a dihybrid cross between two heterozygous individuals.

Question 37

How many chromosomes are present in a man ? 

Answer

A man typically has 46 chromosomes in his somatic cells, which include 44 autosomes and 2 sex chromosomes (XY).

Question 38

Where is a gene present ?

Answer

A gene is present on a chromosome.

Question 39

What type of guineapig is produced in F_₁ generation if a pure white guineapig is crossed with a pure black guineapig?

Answer

A heterozygous black and white guinea pig (black and white coat color) is produced in the F1 generation when a pure white guinea pig is crossed with a pure black guinea pig.

Question 40

In Mendel’s experiment what does ‘Tt’ denote ?

Answer

In Mendel’s experiment, ‘Tt’ denotes a heterozygous genotype.

Question 41

Name a paddy plant which is produced by hybridization process.

Answer

One example of a paddy plant produced by hybridization process is Pusa RH10.

Question 42

Name a high flesh containing fowl produced by hybridization process. 

Answer

One example of a high flesh containing fowl produced by hybridization process is the Cornish Cross breed.

Question 43

What would be the percentage of hybrid tall pea plants in F_₁ generation when a cross makes between two hybrid tall plants?

Answer

If a cross is made between two hybrid tall pea plants (Tt x Tt), then 75% of the offspring in the F1 generation will be hybrid tall plants.

Question 44

Who coined the term ‘Gene’?

Answer

The term “gene” was coined by Danish botanist and geneticist Wilhelm Johannsen in the early 20th century.

Question 45

What would be the percentage of the plants with tall character in F_₁ generation when a pea plant with ‘TT’ genotype is crossed with a pea plant with ‘Tt’ genotype?

Answer

The percentage of plants with the tall character will be 100%.

Question 46

What would be the percentage of the plants with dwarf character in F_₁ generation when a pea plant with “Tt’ genotype is crossed with another pea plant with “Tt’ genotype?

Answer

The percentage of plants with the dwarf character will be 25%.

Question 47

A tall pea plant crossed with a dwarf one produces all tall offsprings-what can you conclude from this?

Answer

The tall pea plant is homozygous dominant (TT) for the height trait, while the dwarf pea plant is homozygous recessive (tt), and the F1 offspring are all heterozygous tall (Tt).

Question 48

Name the law which Mendel found from his monohybrid cross. 

Answer

Mendel’s law of segregation was found in his monohybrid cross.

Question 49

Which law does Mendel derive from his dihybrid cross?

Answer

Mendel’s law of independent assortment was derived from his dihybrid cross.

Question 50

Name one sex-linked or ‘X-chromosome-linked recessive character in a man. 

Answer

Colour blindness is an X-chromosome linked recessive character in man.

Question 51

Name one sex linked or ‘X-chromosome linked dominant character of man. 

Answer

Hypophosphatemia is an X-chromosome linked dominant character in man.

Question 52

Name one autosomal dominant character of man. 

Answer

Huntington’s disease is an example of an autosomal dominant character of man.

Question 53

Name one autosomal recessive character of man. 

Answer

Cystic fibrosis is an example of an autosomal recessive character of man.

Question 54

Name one congenital disease.

Answer

Cerebral palsy is an example of a congenital disease.

Question 55

Out of the following genotypes which are heterozygous ?-AA, Aa, aa, bb, Bb, BB

Answer

Aa, Bb.

Question 56

What would be the percentage of the plants with tall character in F_₁ generation when a pea plant with ‘Tt’ genotype is crossed with a pea plant with ‘tt’ genotype?

Answer

50%

Question 57

Name a sex-linked recessive congenital disease. 

Answer

Hemophilia is a sex-linked recessive congenital disease.

Question 58

What do you mean by gene pool? 

Answer

The gene pool refers to the total genetic information, including all the alleles for every gene, present in a particular population of a species.

Question 59

What do you mean by genome? 

Answer

The genome refers to the complete set of genetic material or DNA present in an organism or cell, including all its genes and non-coding regions.

Question 60

What do you mean by parental generation ?

Answer

The parental generation refers to the starting individuals in a breeding experiment or genetic analysis.

Question 61

Name two hereditary diseases of man. 

Answer

Two hereditary diseases of man are sickle cell anemia and hemophilia.

Question 62

In which year did Mendel publish his work? 

Answer

Mendel published his work on genetics, titled “Experiments on Plant Hybridization,” in the year 1866.

Question 63

Name one scientist of Indian origin who obtained the Nobel Prize for his work in genetics?

Answer

Dr. Hargobind Khorana, who was of Indian origin, obtained the Nobel Prize for Physiology or Medicine in 1968 for his work on the interpretation of the genetic code and its function in protein synthesis.

Short Answer (SA) type questions

Question 1

Define the term Genetics.

Answer

Genetics is the branch of biology that deals with the study of genes, heredity, and genetic variation in living organisms, including how traits are passed down from one generation to the next.

Question 2

Answer

Mendelism refers to the principles of genetics formulated by the Austrian scientist Gregor Mendel based on his experiments with pea plants in the 19th century.

Question 3

Why is Gregor Johann Mendel famous ?

Answer

Gregor Johann Mendel is famous for his experiments with pea plants in the 19th century, which established the basic principles of genetics and how traits are inherited, and paved the way for the modern study of genetics.

Question 4

Where was Mendel’s work first published and in which year was it published?

Answer

Mendel’s work on genetics, titled “Experiments on Plant Hybridization,” was first published in the Proceedings of the Natural History Society of Brno (in German) in 1866.

Question 5

What does Tt denote? What is phenotype?

Answer

Question 6

What are the phenotypic characters of the following genotypes-TT and tt?

Answer

The phenotypic characters of the following genotypes are:

1. TT (homozygous dominant): The phenotype will be tall (expressing the dominant allele for height).
2. tt (homozygous recessive): The phenotype will be short (expressing the recessive allele for height).

Question 7

What do you mean by the term homozygous ?

Answer

Homozygous refers to an individual that has two identical alleles for a particular gene, one inherited from each parent. For example, if an individual has the genotype TT or tt, they are said to be homozygous for that gene. Homozygosity can be either dominant (two dominant alleles) or recessive (two recessive alleles).

Question 8

What do you mean by the term heterozygous ?

Answer

Heterozygous refers to an individual that has two different alleles for a particular gene, one inherited from each parent. For example, if an individual has the genotype Tt, they are said to be heterozygous for that gene. The dominant allele will typically determine the phenotype, as it is expressed over the recessive allele.

Question 9

What do you mean by monohybrid cross?

Answer

Monohybrid cross is a type of genetic cross between two individuals that are heterozygous for one gene, i.e., they differ by one trait. The cross involves studying the inheritance of a single trait or character in the offspring produced by the parents.

Question 10

What is dihybrid cross?

Answer

A Dihybrid cross refers to a cross between two individuals that differ in two traits that are controlled by two different genes.

Question 11

Define the term emasculation?

Answer

Emasculation is the process of removing or destroying the male reproductive organs (stamens) of a flower before they produce pollen. This technique is used in plant breeding to control pollination and facilitate the crossing of two different plants.

Question 12

What is homozygous condition? 

Answer

Homozygous refers to the condition where an individual has two identical alleles for a particular gene. It means that both alleles inherited from the parents are the same – either two dominant alleles or two recessive alleles.

Question 13

What do you mean by the term locus ?

Answer

Locus refers to the specific physical location of a gene or DNA sequence on a chromosome. It is a fixed position that can be identified and used to track the inheritance of a particular gene or trait across generations.

Question 14

What is a recessive character?

Answer

In genetics, a recessive character refers to a trait that is only expressed when an individual has two copies of the same recessive allele. Recessive alleles are usually masked by dominant alleles, which means that an individual with one dominant and one recessive allele will display the dominant trait.

Question 15

What are alleles?

Answer

Alleles are the different forms of a gene that exist at a particular locus (location) on a chromosome. Each individual inherits two alleles for each gene, one from each parent. Alleles can be either dominant or recessive, and they determine the expression of a particular trait or characteristic in an individual.

Question 16

What do you mean by first progeny ? 

Answer

The first progeny, also known as the F1 generation, refers to the offspring resulting from a cross between two parental organisms, and it is the first generation to display the characteristics resulting from the genetic combination of the two parents. The F1 generation is used to study the inheritance of specific traits and determine the patterns of inheritance of those traits in genetics.

Question 17

What is second progeny ?

Answer

The second progeny, also known as the second filial generation or F2 generation, refers to the offspring resulting from a cross between two F1 individuals. The F2 generation is used to study the inheritance of specific traits and to determine the patterns of inheritance of those traits in genetics.

Question 18

How many types of chromosomes are present and what are they?

Answer

There are two types of chromosomes present in most eukaryotic organisms:

1. Autosomal chromosomes: These are the non-sex chromosomes that occur in pairs in diploid cells. Humans have 22 pairs of autosomes, numbered from 1 to 22.
2. Sex chromosomes: These chromosomes determine the sex of an individual. In humans, females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

Question 19

What do you mean by variation ? 

Answer

Variation refers to the differences in physical or genetic traits among individuals of the same species. It can be caused by genetic factors, environmental factors, or a combination of both.

Question 20

Write the practical applications of genetics in human welfare with one example from plant and one example from animals.

Answer

Practical applications of genetics in human welfare include:

• Plant example: Development of disease-resistant crop varieties through genetic engineering
• Animal example: Breeding programs to improve livestock productivity and disease resistance through selective breeding and genetic testing.

Question 21

Name few congenital diseases. 

Answer

Some examples of congenital diseases include Down Syndrome, cystic fibrosis, sickle cell anemia, Tay-Sachs disease, and spina bifida.

Question 22

Why are Watson Crick and Wilkin famous?

Answer

Watson, Crick, and Wilkins are famous for their work on the structure of DNA. They discovered the double-helix structure of DNA, which provided a fundamental understanding of how genetic information is stored and transmitted. Their work laid the foundation for modern molecular biology and genetic research.

Question 23

What do you mean by Genetic Engineering?

Answer

Genetic engineering is the process of manipulating the genetic material (DNA) of an organism to alter its characteristics in a desired way. This involves the insertion, deletion or modification of specific genes or segments of DNA, to introduce new traits or enhance existing ones. It has applications in medicine, agriculture, and biotechnology, among other fields.

Question 24

What do you mean by the term ‘Genome’?

Answer

The term “genome” refers to the complete set of genetic material or DNA present in the cells of an organism. It includes all the genes, non-coding DNA, and other regulatory sequences that are responsible for the organism’s physical and functional traits.

Question 25

What do you mean by the term hybrid?

Answer

In genetics, the term “hybrid” often refers to the offspring of two purebred parents with different traits. Hybrids often exhibit a combination of traits from both parents.

Question 26

What do you mean by a dominant character in heredity? Give one example.

Answer

In heredity, a dominant character is a trait that is expressed when an individual has either one or two copies of the dominant allele. For example, in humans, brown eyes are dominant over blue eyes. If an individual has at least one copy of the brown eye allele, they will have brown eyes, regardless of whether they also have a copy of the blue eye allele.

Question 27

What does Tt denote in case of pea plant in heredity?

Answer

Tt represents the genotype of a pea plant in which one allele for the height of the plant is tall (T) and the other allele is dwarf (t). It is a heterozygous genotype where one allele is dominant and the other is recessive. The dominant allele will determine the phenotype of the pea plant, resulting in a tall plant.

Question 28

Name four recessive characters of man. 

Answer

Here are four recessive characters of humans:

1. Blue eyes
2. Red hair
3. Attached earlobes
4. Hitchhiker’s thumb

Question 29

Among the following characters which are dominant and which are recessive-(a) Tall and dwarf (b) Red and white.

Answer

(a) Tall is dominant and dwarf is recessive.

(b) Red is dominant and white is recessive.

Question 30

State two conclusions derived from Mendel’s monohybrid cross.

Answer

Question 31

(a) What do you mean by heredity? (b) What do you mean by genetics?

Answer

(a) Heredity refers to the transfer of traits or characteristics from parents to offspring through the passing of genetic information (DNA) from one generation to the next.

(b) Genetics is the branch of biology that deals with the study of genes, genetic variation, and heredity in living organisms

Question 32

Who is Mendel? 

Answer

Gregor Johann Mendel (1822-1884) was an Austrian monk and biologist who is famous for his pioneering work on the laws of inheritance in pea plants, which laid the foundation for modern genetics. He is often referred to as the “father of modern genetics.”

Question 33

Why is Mendel famous ?

Answer

Mendel is famous for:

1. Conducting pioneering experiments on pea plants to understand the principles of heredity.
2. Proposing the laws of inheritance, now known as Mendelian laws, which laid the foundation of modern genetics.

Question 34

What do you mean by the terms ‘hybrid’ and ‘pure’ in heredity?

Answer

In heredity, the term ‘hybrid’ refers to the offspring produced from the cross between parents with different characteristics or traits. The hybrid offspring possess a combination of traits inherited from both parents.

On the other hand, the term ‘pure’ in heredity refers to an individual that has the same pair of alleles for a particular trait. Such individuals are known as homozygous and when two homozygous individuals are crossed, their offspring will also be pure for that particular trait.

Question 35

What are the differences between zygote and gamete ?

Answer

Zygote	Gamete
Formed by fusion of two gametes	Formed during gametogenesis
Diploid in nature	Haploid in nature
Gives rise to the embryo	Fuses with another gamete to form a zygote
Produced after fertilization	Produced during meiosis

Question 36

Write a short note on Hybridization?

Answer

Hybridization is the process of crossing two genetically distinct individuals to produce offspring with desirable traits. In agriculture and horticulture, hybridization is commonly used to improve the yield and quality of crops, fruits, and flowers.

Question 37

What will be the phenotypic ratio of round seed to wrinkled seed in F_₁ generation if we crossed a pure round seeded pea plant with pure wrinkled seeded pea plant and in F_₁ generation only round seeded pea plant comes into sight?

Answer

If only round seeded pea plants come into sight in the F₁ generation, it means that the round seed trait is dominant over the wrinkled seed trait. This can only happen if the pure round seeded pea plant is homozygous dominant (RR) and the pure wrinkled seeded pea plant is homozygous recessive (rr).

Question 38

What types of plants will be obtained in F_₁ generation if we crossed a pure white flower plant with a pure red flower plant and only red flower plant comes into sight in F_₁ generation?

Answer

If only red flower plants are observed in F₁ generation after crossing a pure white flower plant with a pure red flower plant, it means that the red color is dominant over white color. Therefore, all the plants in F₁ generation will have a red flower.

Question 39

What is a gene and where is it present?

Answer

A gene is a unit of heredity that is responsible for the transmission of traits from parents to offspring. It is a segment of DNA (deoxyribonucleic acid) that contains the instructions for the development and functioning of an organism. Genes are present in the nucleus of a cell, arranged on the chromosomes in pairs.

Question 40

Name the scientists who rediscovered Mendelism.

Answer

The scientists who rediscovered Mendelism are Hugo de Vries, Carl Correns, and Erich von Tschermak.

Question 41

What do you mean by recessive character and give one example based on animal ?

Answer

In genetics, a recessive character is a genetic trait that is only expressed when an individual inherits two copies of the recessive allele, one from each parent. An example of a recessive character in animals is the white coat color in horses.

Question 42

Differentiate between the terms homozygous and heterozygous ? 

Answer

Homozygous	Heterozygous
It refers to an individual with two identical alleles of a gene	It refers to an individual with two different alleles of a gene
It can be either homozygous dominant (BB) or homozygous recessive (bb)	It is always heterozygous dominant (Bb)

Question 43

What are the differences between homozygote and heterozygote?

Answer

Homozygote	Heterozygote
Organism has two identical alleles for a particular gene	Organism has two different alleles for a particular gene
The alleles can be either dominant or recessive	The dominant allele determines the phenotype, while the recessive allele is hidden in the phenotype

Question 44

When RRYY (round yellow seed) pea plant is crossed with rryy (wrinkled green seed) pea plant, what will be the genotype of F_₁ generation and in dihybrid cross what will be the phenotypic ratio in F_₁ generation?

Answer

When RRYY (round yellow seed) pea plant is crossed with rryy (wrinkled green seed) pea plant, the genotype of F₁ generation will be RrYy (round yellow seed).

In dihybrid cross of RrYy x RrYy, the phenotypic ratio in F₁ generation will be 9:3:3:1, where 9 individuals will have round yellow seeds, 3 individuals will have round green seeds, 3 individuals will have wrinkled yellow seeds and 1 individual will have wrinkled green seeds.

Question 45

State two conclusions derived from Mendel’s monohybrid cross experiment.

Answer

The two conclusions derived from Mendel’s monohybrid cross experiment are

1. The inheritance of a particular trait is determined by discrete units called genes.
2. There are dominant and recessive versions of each gene, and an organism can be homozygous dominant, homozygous recessive, or heterozygous for a trait.

Question 46

What are the differences between dominant and recessive characters ?

Answer

Dominant Characters	Recessive Characters
Expressed in either homozygous or heterozygous condition	Expressed only in homozygous recessive condition
Masks the effect of the recessive allele	Its effect is masked by the dominant allele

Question 47

What are the differences between phenotype and genotype?

Answer

Phenotype	Genotype
The physical appearance or visible traits of an organism	The genetic makeup of an organism
Determined by both genetic and environmental factors	Determined by the combination of alleles inherited from parents
Can be observed and measured easily	Cannot be observed directly and needs genetic analysis

Question 48

 Mention the seven pairs of contrasting characters selected by Mendel Or, Mention four pairs of contrasting (both dominant and recessive) characters used by Mendel in his experiments.

Answer

Mendel selected seven pairs of contrasting characters in pea plants for his experiments on heredity. These are:

1. Seed shape: Round vs. Wrinkled
2. Seed color: Yellow vs. Green
3. Flower color: Purple vs. White
4. Flower position: Axial vs. Terminal
5. Pod color: Yellow vs. Green
6. Pod shape: Inflated vs. Constricted
7. Stem length: Tall vs. Dwarf

Alternatively, four pairs of contrasting characters used by Mendel in his experiments are:

1. Round seeds (dominant) vs. Wrinkled seeds (recessive)
2. Yellow seeds (dominant) vs. Green seeds (recessive)
3. Purple flowers (dominant) vs. White flowers (recessive)
4. Tall stems (dominant) vs. Dwarf stems (recessive)

Question 49

Distinguishes between phenotype and genotype.

Answer

Phenotype	Genotype
External appearance of an organism	Internal genetic makeup of an organism
Observable characteristics or traits of an organism	Inherited genetic information of an organism
Affected by both genes and environment	Affected by genes only
Physical expression of genetic traits	Genetic blueprint of an organism

Question 50

What do you mean by incomplete dominance ?

Answer

Incomplete dominance is a genetic phenomenon in which a heterozygous individual shows an intermediate phenotype, which is a blend of the traits of the two homozygous parents. In other words, neither of the two alleles in the heterozygous condition is completely dominant or recessive. An example of incomplete dominance is the pink color of snapdragons, which is a blend of the red and white parental colors.

Question 51

Why Mendel selected pea plants for his experiments?

Answer

Mendel selected pea plants for his experiments because:

1. Pea plants are easy to cultivate and have a short life cycle, which allows for quick observations and multiple generations to be studied.
2. Pea plants have many distinct and easily identifiable traits or characteristics, such as flower color, seed shape, and pod shape, which made them suitable for studying inheritance patterns.

Question 52

What do you mean by sexual and asexual chromosomes ?

Answer

Sex chromosomes are those chromosomes that determine the sex of an individual. In humans, there are two types of sex chromosomes, X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

Asexual chromosomes are non-sex chromosomes, also known as autosomes, which are present in both males and females in the same number and carry genes that determine most of an individual’s characteristics other than sex. In humans, there are 22 pairs of autosomes.

Question 53

What do you mean by Mendelian error ?

Answer

Mendelian error, also known as transmission distortion, refers to the deviation of observed genotypic or phenotypic ratios from the expected ratios predicted by Mendelian laws. This can occur due to various factors such as genetic linkage, chromosomal aberrations, and non-random mating. It can lead to the inheritance of certain traits in a manner that is not consistent with classical genetics.

Long Answer (LA) type questions

Question 1

Write in brief the life of Gregor Johan Mendel.

Answer

Gregor Johann Mendel (1822-1884) was an Austrian monk and scientist known for his pioneering work in the field of genetics. He was born in a peasant family in a small village in the Austrian Empire (now the Czech Republic). In 1843, he entered the St. Thomas Monastery in Brno, where he spent most of his life.

Mendel was a self-taught scientist who conducted experiments on the inheritance of traits in pea plants from 1856 to 1863. He discovered the principles of heredity by studying the patterns of inheritance of traits such as seed colour, flower colour, and plant height. He proposed the concepts of dominant and recessive traits, and the laws of segregation and independent assortment, which form the basis of modern genetics.

Mendel’s work went largely unnoticed during his lifetime, but his experiments were rediscovered in the early 20th century and became the foundation of modern genetics. Mendel died in 1884, at the age of 61, due to kidney disease. He is widely regarded as the father of genetics and his work remains influential in the field of biology.

Question 2

Answer

(a) Heredity is the process by which traits or characteristics are passed from one generation to the next through the transmission of genetic information.

(b) The three laws of Mendel are:

1. Law of Segregation: Each individual has two alleles for a given trait, and these alleles segregate (separate) during the formation of gametes. Each gamete receives only one allele from each parent.
2. Law of Independent Assortment: Genes for different traits are inherited independently of each other. In other words, the inheritance of one trait does not affect the inheritance of another.
3. Law of Dominance: In a heterozygous individual (one with two different alleles for a trait), the dominant allele will be expressed while the recessive allele will be masked.

Question 3

(a) What is a monohybrid cross? (b) Explain the law of Mendel with the help of monohybrid cross. Or, Give an example of monohybrid cross and explain it. Or, How did Mendel explain the occurrence of tallness of all plants in the F_₁ generation in his experiment of Monohybrid cross? Discuss in brief how did he also explain the occurrence of growing tall and dwarf pea plants in the ratio of 3: 1 in the F₂ generation in the same experiment. Mention the genotypic ratio obtained in the F₂ generation of the same cross. 

Answer

(a) A monohybrid cross is a type of genetic cross in which a single trait is being studied. It involves the mating of two individuals that are heterozygous for the trait of interest, resulting in the offspring being produced with a 3:1 ratio of dominant to recessive phenotypes.

(b) Mendel’s law of segregation states that each individual has two alleles for each trait, and these alleles separate during gamete formation so that each gamete receives only one allele. The law was derived from Mendel’s monohybrid cross experiment, where he crossed purebred tall and purebred dwarf pea plants. He found that the offspring produced in the F1 generation were all tall, indicating that the tall trait was dominant. However, in the F2 generation, the ratio of tall to dwarf plants was 3:1, suggesting that the trait was determined by two factors (later termed alleles) and that the recessive allele only appeared in plants that inherited two copies of it. This demonstrated the principle of segregation, where the alleles of a gene separate during gamete formation, with each gamete receiving only one allele, which is randomly determined.

Question 4

 Explain monohybrid cross with an example of animal.

Answer

Monohybrid cross is a genetic cross between two individuals that differ in only one trait or character. In this type of cross, only one pair of contrasting traits or alleles is considered.

For example, consider a monohybrid cross between two guinea pigs, one with black fur and the other with white fur. The black fur is dominant and the white fur is recessive. Let B be the allele for black fur and b be the allele for white fur. The genotype of the black-furred guinea pig can be represented as BB or Bb, while the genotype of the white-furred guinea pig is bb.

When these two guinea pigs are crossed, the offspring are referred to as the first filial generation or F1 generation. The F1 generation will have a heterozygous genotype, which is Bb, because they inherited one allele for black fur (B) and one allele for white fur (b) from their parents.

The phenotypic ratio of the F1 generation will be 100% black fur since the black fur is dominant over the white fur. However, the genotypic ratio will be 1:2:1 (BB:Bb:bb), following the principles of Mendelian genetics.

Question 5

Explain the terms Phenotype and Genotype with the help of Mendel’s Monohybrid cross experiment.

Answer

Question 6

Explain what would be the result if a ‘tall’ pea plant (dominant- TT) is crossed with a dwarf one (recessive – dd) up to the F_₁ generation.

Answer

If a ‘tall’ pea plant (dominant – TT) is crossed with a dwarf one (recessive – dd) up to the F₁ generation, all the F₁ generation plants would be heterozygous tall (Tt) as T is dominant over d. This is because each parent will contribute one allele to their offspring, and the dominant allele (T) from the tall plant will mask the recessive allele (d) from the dwarf plant. The genotype of the F₁ plants will be Tt, while their phenotype will be tall because of the presence of at least one dominant allele.

Question 7

Explain what would be the ratio of the pure red and the pure white flower-bearing pea plants in the F₂ generation, when a cross is made between two pea plants, one bearing pure red flower (dominant) and the other bearing pure white flower (recessive).

Answer

When a cross is made between two pea plants, one bearing pure red flower (dominant) and the other bearing pure white flower (recessive), the F1 generation will all have a red flower phenotype as it is dominant over the white flower. However, they will be heterozygous (Rr) as they have inherited one dominant red allele (R) and one recessive white allele (r) from their parents.

When the F1 generation is self-crossed, the resulting F2 generation will exhibit a phenotypic ratio of 3:1 for red to white flowers. This is because the heterozygous F1 plants can produce two types of gametes, one carrying the dominant red allele (R) and the other carrying the recessive white allele (r), in equal proportions. When these gametes combine randomly in fertilization, they can give rise to three possible genotypes: RR (pure red), Rr (red), and rr (pure white) in a ratio of 1:2:1. Hence, the resulting phenotypic ratio of the F2 generation will be 3:1 for red to white flowers.

Question 8

With the help of the Mendel’s monohybrid cross explain the term dominant and recessive.

Answer

In Mendel’s monohybrid cross, two pea plants with contrasting traits, one with dominant and other with recessive traits, were crossed. The offspring produced in the F1 generation showed only the dominant trait. This indicates that the dominant trait is expressed over the recessive trait in the offspring. When these F1 plants were self-pollinated or cross-pollinated with another F1 plant, the F2 generation was produced. In this generation, the ratio of dominant to recessive traits was 3:1. This shows that the recessive trait is not expressed in the F1 generation but is present in the genes, and it can reappear in the F2 generation. Thus, the dominant trait is expressed over the recessive trait in heterozygous individuals. The trait that is expressed in the presence of its contrasting trait is called a dominant trait, while the trait that is not expressed in the presence of its contrasting trait is called a recessive trait.

Question 9

What will be your comment derived from the result of experiment on the monohybrid cross?

Answer

The result of the monohybrid cross follows the expected Mendelian ratio of 3:1, it suggests that the traits being observed are governed by a single gene and that one allele is dominant over the other. The experiment also indicates that the alleles segregate and assort independently during gamete formation, following Mendel’s Law of Segregation and Law of Independent Assortment. These observations provide a fundamental understanding of the principles of inheritance and genetic variation.

Question 10

(a) Write about the scientific name of Drosophila. (b) Explain monohybrid cross of Drosophila through a checker board.

Answer

(a) The scientific name of Drosophila is Drosophila melanogaster. It is a species of fruit fly that has been widely used in genetics research.

(b) Monohybrid cross of Drosophila can be explained using a checkerboard. Let’s consider the cross between a homozygous dominant (BB) and a homozygous recessive (bb) Drosophila. The genotype of F1 generation will be Bb (heterozygous). To determine the genotype and phenotype of F2 generation, we can use a checkerboard:

	B	b
B	BB	Bb
b	Bb	bb

From this checkerboard, we can see that there are 3 possible genotypes in the F2 generation, i.e. BB, Bb, and bb. The ratio of these genotypes will be 1:2:1, which is the same as the monohybrid ratio derived by Mendel. Similarly, we can determine the phenotypic ratio of the offspring by counting the number of dominant (B) and recessive (b) traits. In this case, the phenotypic ratio will also be 3:1, where 3 individuals will have the dominant trait and 1 individual will have the recessive trait.

Question 11

(a) Write the law of independent assortment. (b) If we make the cross between pure red flower (dominant) with pure newer than what will be the ratio in F_₁ generation?

Answer

(a) The law of independent assortment states that the inheritance of one pair of contrasting characters (alleles) is independent of the inheritance of another pair of contrasting characters (alleles).

(b) If we make the cross between pure red flower (dominant) with pure blue flower, the ratio of the F₁ generation will be all plants with purple flowers. This is because the alleles for red and blue flower color will combine to form a heterozygous genotype (RrBb) which expresses incomplete dominance resulting in the formation of purple flowers.

Question 12

Explain dominant, recessive characters and phenotypic and genotypic characters through Mendel’s monohybrid cross.

Answer

Mendel’s monohybrid cross was conducted between pea plants having one pair of contrasting characters, for example, tall (dominant) and dwarf (recessive). Here, ‘T’ represents the dominant allele for tallness and ‘t’ represents the recessive allele for dwarfness.

When a homozygous tall plant (TT) is crossed with a homozygous dwarf plant (tt), the F1 generation consists of only tall plants (Tt). This indicates that the dominant trait (tallness) is expressed over the recessive trait (dwarfness) in the heterozygous condition (Tt).

In the F2 generation, when the heterozygous tall plants (Tt) are self-pollinated, the genotypic ratio is 1:2:1 (TT:Tt:tt) and the phenotypic ratio is 3:1 (tall:dwarf). This is because during gamete formation, the alleles segregate independently of each other and combine randomly in the zygote, leading to a variety of genotypic and phenotypic ratios.

Question 13

State four pairs of contrasting characters used in his experiment mentioning the dominant and recessive traits. Write the inference drawn from the monohybrid cross.

Answer

Mendel used several pairs of contrasting characters in his experiments, four of which are as follows:

1. Round and Wrinkled Seeds: Round (dominant) and wrinkled (recessive) seed shape were used as contrasting characters.
2. Yellow and Green Pea Pods: Yellow (dominant) and green (recessive) pea pod color were used as contrasting characters.
3. Purple and White Flowers: Purple (dominant) and white (recessive) flower color were used as contrasting characters.
4. Tall and Dwarf Plants: Tall (dominant) and dwarf (recessive) plant height were used as contrasting characters.

Inference drawn from the monohybrid cross:

1. The inheritance of each trait is determined by the factors (now known as genes) that are passed down from parent to offspring.
2. The two copies of each gene (one from each parent) segregate during gamete formation and then come back together randomly during fertilization.
3. The dominant allele will always be expressed in the phenotype when present, while the recessive allele is only expressed in the phenotype when it is present in the homozygous form.
4. The phenotype observed in the F1 generation is determined by the dominant allele, but the recessive allele is not lost and can reappear in the F2 generation.

Question 14

(a) What is hybridization? (b) What is a dihybrid cross ? (c) Differentiate homozygous and heterozygous.

Answer

(a) Hybridization is the process of crossing two genetically different individuals to produce offspring with desirable traits or characteristics.

(b) A dihybrid cross is a genetic cross between two individuals that differ in two traits or characteristics, involving the inheritance of two pairs of alleles.

(c) Homozygous refers to an individual having identical alleles for a particular gene, whereas heterozygous refers to an individual having two different alleles for a particular gene.

Question 15

(a) What is a dihybrid cross? (b) Explain the dihybrid cross with a checkerboard.

Answer

(a) Dihybrid cross refers to a cross between two individuals that differ in two traits that are controlled by two different genes.

(b) To find out whether one pair of alleles affects or influences the inheritance pattern of other alleles. In a dihybrid cross, Mendel considered two traits simultaneously. A cross conducted between two pure parents differing in two pairs of contrasting characters. He studied round and wrinkled seed characters along with yellow and green colours.

Gametes	yr	yr
YR	YyRr	YyRr
YR	YyRr	YyRr

Yellow and round are dominant alleles so in an F1 generation all plants with yellow and round are used. Above table is a punnet square for the F1 generation.

Mendel allowed self-pollination in each hybrid of F1 and collected seeds separately and obtained F2 generation. a checkerboard or punnet square for F2 generation is shown in the image. He found seeds of four types in 9:3:3:1 ratio which is a dihybrid ratio.

Question 16

(a) What is hybrid ? (b) if a hybrid black haired Guineapig is crossed with a white haired Guineapig, what will be the phenotypes of the Guineapigs of the First filial (F_₁) generation and why-Explain with reasons.

Answer

Question 17

Explain the dihybrid cross of Mendel with an example from Guineapig.

Answer

A dihybrid cross is a genetic cross between two individuals that differ in two traits. For example, in guinea pigs, one trait could be coat color (black or white) and the other trait could be hair length (short or long). To conduct a dihybrid cross, the parents must be pure for each trait.

If a hybrid black-haired guinea pig (Bb) is crossed with a white-haired guinea pig (bb), the Punnett square for the F1 generation would show that all offspring would have black hair (Bb) because black is dominant over white. However, all F1 individuals would be heterozygous (Bb) for the hair colour trait.

To determine the possible genotypes and phenotypes of the F2 generation, a Punnett square can be used. The genotypes of the F2 offspring would be in a ratio of 9:3:3:1, with 9 having black and short hair, 3 having black and long hair, 3 having white and short hair, and 1 having white and long hair. This ratio can be explained by the law of independent assortment, which states that each pair of alleles segregates independently of other pairs of alleles during gamete formation.

Question 18

Write briefly about sex determination.

Answer

Sex determination is the process by which an individual is identified as male or female. In humans and most animals, sex is determined by the presence or absence of specific sex chromosomes. Females typically have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The presence of the Y chromosome determines maleness, while the absence of it results in femaleness. In some species, environmental factors may also play a role in sex determination. For example, in some reptiles, the temperature of the egg incubation determines the sex of the offspring.

Question 19

(a) Which one is the dominant character and what will be the ratio of F_₁ generation, if we crossed round seed producing pea plant with wrinkled seed producing pea plant and in F_₁ generation we get round seed producing pea plant. (b) If black is a dominant character and white is a recessive character then what will be the result of the following cross-

(i) Pure black (BB) × Pure white (bb)

(ii) Hybrid black (Bb) × Pure white (bb)

Answer

(a) Round seed producing pea plant is the dominant character. The ratio of F₁ generation will be 1:1.

(b) (i) All the offspring will be hybrids with the genotype Bb, and all of them will have black color.

(ii) Half of the offspring will be hybrids with the genotype Bb and black color, and the other half will be pure white with the genotype bb.

(c) The result in F₁ generation indicates that the red flowered plant is dominant and the white flowered plant is recessive. All the offspring in F₁ generation will have the genotype Rr and will show the dominant phenotype of red flower color.

Question 20

Why the following scientists are famous ? (a) Muller, (b) Watson, Crick and Wilkins, (c) Hargobind Khorana.

Answer

(a) Muller, also known as Hermann J. Muller, is famous for his work on the genetic effects of radiation and his discovery of the mutagenic properties of X-rays.

(b) Watson, Crick, and Wilkins are famous for their work on the structure of DNA. They proposed a double helix model for the structure of DNA, which revolutionized the field of genetics.

(c) Hargobind Khorana is famous for his work on the genetic code and his contributions to the synthesis of DNA. He helped to decipher the genetic code and developed methods for synthesizing DNA, which are used in genetic engineering today.

Question 21

Discuss the application of the science of heredity in human welfare.

Answer

The application of the science of heredity in human welfare.

1. Prediction and prevention of genetic disorders through genetic counseling and testing.
2. Development of genetically modified crops for better yield, disease resistance, and nutritional value.
3. Identification and selection of superior livestock for breeding.
4. Development of new medical treatments and therapies based on genetic engineering.
5. Understanding the genetic basis of complex diseases to develop targeted treatments.
6. Forensic investigations and identification of individuals based on DNA analysis.

Question 22

Why Mendel chose pea plants ?

Answer

Mendel chose pea plants for his experiments because:

1. Pea plants have easily identifiable and distinguishable traits such as seed shape, flower color, pod color, etc.
2. Pea plants have a short life cycle and produce a large number of offspring.
3. Pea plants are easy to cultivate and crossbreed.
4. Pea plants have both self-fertilization and cross-fertilization capabilities.

Question 23

(a) If a Tt plant is crossed with tt pea plant, how many phenotypes will be observed in F_₁ generation? (b) Mention one use of genetics in the welfare of plant and one for animal.

Answer

(a) In the F₁ generation of a cross between Tt and tt plants, only one phenotype (Tt) will be observed because the dominant allele masks the recessive allele in heterozygous individuals.

(b) One use of genetics in the welfare of plants is the development of genetically modified crops that can resist pests, tolerate harsh environmental conditions, and produce higher yields. An example of genetics in the welfare of animals is the breeding of disease-resistant livestock through selective breeding and genetic engineering techniques.

Question 24

Give reasons behind the success of Mendel. 

Answer

There were several reasons behind the success of Mendel in his experiments on inheritance, such as:

1. Mendel’s choice of pea plants allowed him to control the crosses and observe the inheritance of specific traits.
2. Mendel’s use of statistical analysis in his experiments allowed him to make accurate predictions about the inheritance of traits.
3. Mendel’s experimental design was simple and easy to replicate, allowing others to confirm his results.
4. Mendel’s focus on one trait at a time allowed him to identify and describe the basic principles of inheritance.
5. Mendel’s use of mathematical ratios and laws of probability helped him to accurately predict the outcome of genetic crosses.