Chapter 3: Heredity and Common Genetic Diseases | Chapter Solution Class 10

Book Name	: Life Science And Environment
Subject	: Life Science
Class	: 10 (Madhyamik)
Publisher	: Santra Publisher Pvt. Ltd
Unit Name	: Heredity and Common Genetic Diseases (3rd Chapter)

Multiple Choice Questions :

Question 1

Mendel’s choice of contrasting characters from pea plants are

1. 7 pairs
2. 9 pairs
3. 6 pairs
4. 8 pairs

Answer

7 pairs

Explanation

Mendel chose 7 pairs of contrasting characters from pea plants for his experiments. These pairs of characters were:

• Seed color (green vs. yellow)
• Seed shape (round vs. wrinkled)
• Pod color (green vs. yellow)
• Pod shape (inflated vs. constricted)
• Flower color (purple vs. white)
• Plant height (tall vs. dwarf)
• Flower position (axial vs. terminal)

Question 2

The ratio of phenotype in the monohybrid cross of Mendel was

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

Answer

3: 1.

Explanation

In a monohybrid cross, the phenotypic ratio is 3 : 1. This means that 3 out of 4 offspring will express the dominant trait, while 1 out of 4 will express the recessive trait. The recessive trait is only expressed when both copies of the gene are recessive.

Question 3

When a hybrid black guinea pig is crossed with a pure white guineapig the offspring of F₁ will be

1. 1 : 2 : 1
2. 1 : 1
3. 3 : 1
4. None of them

Answer

1 : 2 : 1.

Explanation

When a hybrid black guinea pig (Bb) is crossed with a pure white guinea pig (bb), the offspring of the F1 generation will be 1 : 2 : 1 for the genotypes BB : Bb : bb, and 3 : 1 for the phenotypes black : white.

Question 4

Phenotype result of Mendel’s dihybrid cross will bet.

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

Answer

9 : 3 : 3 : 1.

Explanation

In a dihybrid cross, two genes are considered at the same time. The phenotypic ratio of a dihybrid cross is 9 : 3 : 3 : 1. This means that 9 out of 16 offspring will have the dominant phenotype for both genes, 3 out of 16 will have the dominant phenotype for one gene and the recessive phenotype for the other gene, 3 out of 16 will have the recessive phenotype for one gene and the dominant phenotype for the other gene, and 1 out of 16 will have the recessive phenotype for both genes.

Question 5

Protanopia is a type of

1. Haemophilia
2. Thalassemia
3. Colorblindness
4. None of them

Answer

Colorblindness.

Explanation

Protanopia is a type of red-green colour blindness. It is caused by a lack of red pigment in the retina. This means that people with protanopia have difficulty seeing reds and greens. They may also see other colours differently, such as yellows and oranges.

Question 6

Among the following which one is applicable to a normal male man?

1. 44A + XY
2. 44A + XYY
3. 44A + XX
4. 44A + XXY

Answer

44A + XY

Question 7

The chromosome theory of inheritance was proposed by

1. Morgan
2. Sutton and Bover.
3. Mendel
4. Lamarck

Answer

Sutton and Bover

Explanation

The chromosome theory of inheritance was proposed by (b) Sutton and Bover. Walter Sutton and Theodor Bover independently proposed the chromosome theory of inheritance in the early 20th century. The theory suggests that genes are located on chromosomes, and the behaviour of chromosomes during meiosis explains Mendelian inheritance patterns.

Question 8

The pea plants produced from the seeds obtained from a cross between hybrid tall (Tt) and pure dwarf (tt) pea plants will be

1. All dwarf
2. All tall
3. 75% tall, 26% dwarf
4. 50% tall, 50% dwarf

Answer

50% tall, 50% dwarf

Explanation

When a hybrid tall (Tt) pea plant is crossed with a pure dwarf (tt) pea plant, the resulting pea plants will exhibit a phenotypic ratio of 1:1 for tall to dwarf. The genotype of the offspring will be either Tt (tall) or tt (dwarf) because the pure dwarf parent contributes only “t” alleles.

Question 9

The genetic constitution for which a characteristic feature in an organism is expressed is called

1. Phenotype
2. Genotype
3. Dominance
4. Hybrid

Answer

Genotype

Question 10

The process of fertilization of the female gamete with a male gamete of the same plant is called

1. Selfing
2. Back cross
3. Test cross
4. Hybrid

Answer

Selfing

Explanation

The process of fertilization of the female gamete with a male gamete of the same plant is called (a) Selfing. Selfing, or self-pollination, occurs when the pollen from a flower’s stamen fertilizes the ovule of the same flower or another flower on the same plant. This can lead to the production of offspring that are genetically identical or very similar to the parent plant.

Question 11

When both the alleles of a gene are equally expressive, is called

1. Codominance
2. Dominance
3. Recessiveness
4. Phenotype

Answer

Codominance

Explanation

When both alleles of a gene are equally expressive, it is called (a) Codominance. In codominance, both alleles contribute to the phenotype in a distinct and distinguishable way. This is in contrast to dominance, where one allele masks the expression of the other, and recessiveness, where one allele is completely masked in the presence of the dominant allele.

Question 12

The F₂ generation of a cross produced an identical phenotypic and genotypic ratios. It is not an expected Mendelian result and can be attributed to.

1. Homologous pairs
2. Independent assortment
3. Linkage.
4. Incomplete dominance

Answer

incomplete dominance

Explanation

Incomplete dominance is a type of gene expression in which neither allele of a gene is completely dominant over the other allele. This means that both alleles are expressed in the heterozygous individual, resulting in a phenotype that is intermediate between the phenotypes produced by the two homozygous genotypes.

Question 13

The factors which represent the contrasting pairs of characters are called

1. Dominant and recessive
2. Determinants
3. Homologous pairs
4. Alleles

Answer

alleles

Explanation

The factors which represent the contrasting pairs of characters are called (d) Alleles. Alleles are different versions or forms of a gene that occupy the same position (locus) on homologous chromosomes. These alleles can be either dominant or recessive, and they determine the expression of specific traits in an organism.

Question 14

The monohybrid genotypic ratio 1 : 2 : 1 in F₂-generation indicates

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

Answer

Segregation

Question 15

The first work on genetics was done by

1. Lamarck
2. Mendel
3. Vries
4. Darwin

Answer

Gregor Mendel

Question 16

The discipline which deals with the study of the inheritance of characters is

1. Cytology
2. Genetics
3. Darwinism
4. Evolution

Answer

Genetics

Explanation

The discipline that deals with the study of the inheritance of characters is (b) Genetics. Genetics is the branch of biology that focuses on the study of genes, heredity, and the variation of organisms.

Question 17

A cross between unlike organisms is called

1. Test cross
2. Heterosis
3. Back cross
4. Hybrid

Answer

Hybrid

Explanation

A cross between unlike organisms is called (d) Hybrid. Hybridization involves mating or crossing individuals from different species, varieties, or breeds.

Question 18

Genes do not occur in pairs in

1. Endosperm cells
2. Zygote
3. Gamete
4. somatic cell

Answer

Gametes

Explanation

Genes do not occur in pairs in (c) Gamete. Gametes are reproductive cells (sperm and egg cells in animals, and pollen and ovules in plants), and they are haploid, meaning they contain half the number of chromosomes compared to somatic cells.

Question 19

The position of gene on the chromosome is called

1. Locus
2. Nucleosome
3. Factor
4. Cistron

Answer

Locus

Explanation

The position of a gene on a chromosome is called a “Locus.” Therefore, the correct option is (a) Locus. A locus is a specific place on a chromosome where a particular gene is located. The other terms listed—nucleosome, factor, and cistron—refer to different aspects of genetics and molecular biology.

Question 20

Which of the following crosses would produce a genotype ratio 1 : 2 : 1 in F₂?

1. Ab × Ab
2. ab × ab
3. Ab × ab
4. AB × AB

Answer

Ab × Ab

Question 21

Mendel is popular for postulating

1. Cell theory
2. Laws of inheritance
3. Linkage theory
4. Origin of species

Answer

laws of inheritance

Explanation

Mendel is popular for postulating the “Laws of inheritance.” Specifically, Gregor Mendel formulated the principles of heredity based on his experiments with pea plants. His work, conducted in the mid-19th century, laid the foundation for modern genetics.

Question 22

The phenomenon which defines the independent assortment is

1. Segregation
2. Dominance
3. Crossing over
4. Linkage

Answer

Segregation

Explanation

Segregation is the process by which homologous chromosomes separate during meiosis, resulting in each gamete receiving one allele from each pair of alleles. This process ensures that the alleles of different genes are inherited independently of one another.

Question 23

The number of characters studied by Mendel in Pea was

1. 5
2. 4
3. 7
4. 6

Answer

7

Explanation

The number of characters studied by Mendel in peas was 7. Mendel’s experiments with pea plants involved the study of traits (or characters) such as seed colour, seed shape, flower colour, flower position, pod colour, pod shape, and stem length. These traits were inherited in a predictable manner, and Mendel’s work laid the foundation for the principles of heredity.

Question 24

A haploid set of all the genes present in a gametes is called

1. Genome
2. Linkage group
3. Phenotype
4. Genotype

Answer

Genome

---

Fill in the Blanks :

Question 1

The phenotypic ratio in the monohybrid cross was ____.

Answer

The phenotypic ratio in the monohybrid cross was 3:1.

Question 2

In ____ the affected person fails to recognise the red colour.

Answer

In colour blindness, the affected person fails to recognize the red colour.

Question 3

Incomplete dominance found in ____ plant.

Answer

Incomplete dominance found in snapdragon plant.

Question 4

Mendel has chosen ____ contrasting characteristics in pea plants.

Answer

Mendel has chosen 7 contrasting characteristics in pea plants.

Question 5

Autosomal genetic disease is ____.

Answer

Autosomal genetic disease is inherited.

Mention True or False :

Question 1

Another name for haemophilia disease is Christmas disease.

Answer

False. Christmas disease is another name for haemophilia B, which is a blood clotting disorder. Haemophilia A is another type of blood clotting disorder, and it is denoted by the genotype ‘XX’.

Question 2

Pure tall is denoted by ‘TT’

Answer

True.

Question 3

44A + XXY is a normal man’s chromosome number.

Answer

False. A normal man’s chromosome number is 44A + XY.

Question 4

Protanopia is a type of haemophilia.

Answer

False. Protanopia is a type of colour blindness, and it is not related to haemophilia.

Question 5

The sex chromosome of males is YY.

Answer

False. The sex chromosome of males is XY. The sex chromosome of females is XX.

Column matching :

Question 

Left Column	Right Column
A. Pure tall	(i) Tt
B. Hybrid tall	(ii) Test cross
C. Pure dwarf	(iii) TT
D. T T × Tt	(iv) tt
	(v) Back cross

Answer

Left Column	Right Column
A. Pure tall	(i) TT
B. Hybrid tall	(ii) Tt
C. Pure dwarf	(iv) tt
D. T T × Tt	(v) Back cross

Question 

Left Column	Right Column
A. Haemophilia	(i) Red colourblindness
B. Thalassemia	(ii) Heriditary unit
C. Protanopia	(iii) Christman disease
D. Gene	(iv) Genetic counselling

Answer

Left Column	Right Column
A. Haemophilia	(i) Sex-linked recessive disorder
B. Thalassemia	(ii) Hereditary unit
C. Protanopia	(iii) Red colourblindness
D. Gene	(iv) Genetic counselling

Very Short Answer (VSA) Type Questions :

Question 1

Who is the father of genetics?

Answer

Gregor Mendel is considered the father of genetics.

Question 2

‘Tt’ is homozygous or heterozygous?

Answer

‘Tt’ is heterozygous.

Question 3

What is the genotypic ratio?

Answer

The genotypic ratio is the ratio of the different genotypes in a population.

Question 4

Give the ratio of phenotypes in a monohybrid cross.

Answer

The ratio of phenotypes in a monohybrid cross is 3:1.

Question 5

What do you mean by trait?

Answer

A trait is a characteristic that is inherited from parents to offspring.

Question 6

When a cross takes place between two hybrid black guineapigs, what will be the phenotype ratio of black and white guineapigs?

Answer

The phenotype ratio of black and white guinea pigs will be 3:1. This means that there will be three times as many black guinea pigs as white guinea pigs.

Question 7

Define character.

Answer

A character is a physical or behavioural trait that can be observed and measured. Characters are often used to study inheritance.

Question 8

What is a hybrid?

Answer

A hybrid is an individual that has two different alleles for a particular trait.

Question 9

What do you mean by F₁ generation?

Answer

The F₁ generation is the first generation of offspring produced from a cross between two parents with different genotypes.

Question 10

Define F₂ generation.

Answer

The F₂ generation is the second generation of offspring produced from a cross between two F1 individuals.

Question 11

What is selfing?

Answer

Selfing is the process of breeding an individual with itself. This can be done to produce offspring that are homozygous for a particular trait.

Question 12

What do you mean by parental generation?

Answer

The parental generation is the first generation of parents that are used to produce offspring.

Question 13

Mendel used which organism as his experimental sample?

Answer

Mendel used pea plants as his experimental sample. He chose pea plants because they have a short generation time and are easy to cross.

Question 14

What were the two contrasting colours of flowers considered by Mendel?

Answer

The two contrasting colours of a flower considered by Mendel were purple and white.

Question 15

Mention the types of colourblindness.

Answer

There are two types of colourblindness: red-green colourblindness and blue-yellow colourblindness.

Question 16

What is the ratio of progenies obtained in the case of a cross between a heterozygous dominant and a homozygous recessive?

Answer

The ratio of progenies obtained in the case of a cross between a heterozygous dominant and a homozygous recessive is 3:1.

Question 17

Give an example of a plant which shows incomplete dominance in flower colour.

Answer

An example of a plant which shows incomplete dominance in flower colour is the snapdragon. Snapdragons can have red, white, or pink flowers.

Question 18

Give the two forms of thalassemia.

Answer

There are two main forms of thalassemia: alpha thalassemia and beta thalassemia.

Question 19

Who proposed the chromosomal theory of inheritance?

Answer

The chromosomal theory of inheritance was given by Boveri and Sutton in the early 1900s.

Question 20

Who proposed linkage theory and sex-linked inheritance?

Answer

Linkage theory and sex-linked inheritance were proposed by Archibald Garrod in 1902.

Short Answer (SA) Type Questions :

Question 1

What is heredity?

Answer

Heredity is the passing of traits from parents to offspring. It is the mechanism by which characteristics, resemblances, and differences are passed down from one generation to the next.

Question 2

What is mutation?

Answer

Mutation is a change in the DNA sequence of an organism. Mutations can be caused by environmental factors, such as radiation, or by random errors during DNA replication. Mutations can be harmful, beneficial, or neutral.

Question 3

What is the variation?

Answer

Variation is the difference in the characteristics of individuals within a population. Variation is caused by a combination of factors, including heredity and environment. Variation is important for evolution, as it allows for the selection of beneficial traits.

Question 4

Define physiological variation.

Answer

Physiological variation is the variation in the function of an organism’s body. This type of variation is caused by differences in the genes that control how the body works.

Question 5

What do you mean by continuous variation?

Answer

Continuous variation is the variation in the size or shape of a trait that can be measured on a continuous scale. For example, height is a continuous trait that can vary from very short to very tall. Continuous variation is caused by the interaction of many genes.

Question 6

What is hybridization?

Answer

Hybridization is the crossing of two different varieties or species of plants or animals. Hybridization is often used to create new varieties with desirable traits.

Question 7

What is a monohybrid cross?

Answer

A Monohybrid cross is a genetic cross between two individuals that differ in only one trait. For example, a monohybrid cross could be between a tall pea plant and a short pea plant.

Question 8

What do you mean by 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 9

What is a recessive gene?

Answer

A recessive gene is a gene that is only expressed when it is present in two copies. Recessive genes are often associated with traits that are considered to be undesirable, such as albinism or cystic fibrosis.

Question 10

Define cross-pollination.

Answer

Cross-pollination is the transfer of pollen from the anther of one flower to the stigma of another flower. Cross-pollination is important for plant reproduction, as it allows for the mixing of genes from different plants.

Question 11

What is incomplete dominance?

Answer

Incomplete dominance is a type of genetic inheritance in which the phenotype of the heterozygous offspring is intermediate between the phenotypes of the two homozygous parents.

Question 12

What is the dominant gene?

Answer

A dominant gene is a gene that is always expressed when it is present in the genotype, even if it is only present in one copy.

Question 13

What do you mean by a homozygous organism?

Answer

A homozygous organism is an organism that has two copies of the same allele for a particular gene. For example, a homozygous pea plant for tallness would have two copies of the tallness allele.

Question 14

What do you mean by a heterozygous organism?

Answer

A heterozygous organism is an organism that has two different alleles for a particular gene. For example, a heterozygous pea plant for tallness would have one copy of the tallness allele and one copy of the shortness allele.

Question 15

What is pure breeding variety?

Answer

Pure breeding variety is a variety of organisms that is homozygous for all of its genes. This means that all of the offspring of a pure breeding variety will have the same genotype and phenotype.

Question 16

What is a test cross?

Answer

A test cross is a genetic cross between an individual of an unknown genotype and an individual that is homozygous recessive for the trait in question. The purpose of a test cross is to determine the genotype of the individual unknown genotype.

Question 17

State Mendel’s law of segregation.

Answer

The law of segregation states that actors passed from one generation to another in an unaltered manner; they separate during gamete formation, reunite during fertilization and pass to the next generation.

Question 18

State two symptoms of thalassemia.

Answer

Two symptoms of thalassemia are:

• Anaemia, is a condition in which the body does not have enough red blood cells.
• Yellowing of the skin, is caused by a buildup of bilirubin, a substance that is produced when red blood cells break down.

Question 19

What is Mendelism?

Answer

Mendelism is the study of inheritance patterns. It is named after Gregor Mendel, who was the first scientist to study inheritance patterns in a systematic way.

Question 20

State two differences between the back cross and the test cross.

Answer

Here are two differences between the back cross and the test cross:

• The back cross is a cross between an F₁ hybrid and a homozygous recessive parent, while the test cross is a cross between an individual of an unknown genotype and a homozygous recessive parent.
• The purpose of a back cross is to verify the genotype of the F₁ hybrid, while the purpose of a test cross is to determine the genotype of an individual of an unknown genotype.

Long Answer (LA) Type Questions :

Question 1

Why did Mendel choose pea plants as his experimental organism?

Answer

The reasons why Mendel chose pea plants as his experimental organism:

1. They are easy to grow and breed. Pea plants are relatively easy to care for and reproduce, making them ideal for experiments.
2. They have a short life cycle. Pea plants complete their life cycle in a relatively short period of time, which allowed Mendel to conduct many experiments in a short period of time.
3. They have a variety of easily observable traits. Pea plants have a number of easily observable traits, such as seed color, seed shape, plant height, and flower color. This made it easy for Mendel to track how these traits were inherited from generation to generation.
4. They are self-pollinating plants. Pea plants can self-pollinate, meaning that they can produce pollen that can fertilize their own eggs. This allowed Mendel to produce pure-breeding lines of pea plants with specific traits.

Question 2

Describe Mendel’s work on the pea plant.

Answer

Mendel’s work on the pea plant, also known as Mendelian genetics:

1. Gregor Mendel (1822-1884) was an Austrian scientist and Augustinian friar who conducted groundbreaking research on pea plants in the mid-19th century.
2. He chose pea plants for their easily observable traits and ability to self-fertilize or cross-fertilize.
3. Mendel conducted controlled experiments, carefully tracking the inheritance of specific traits over multiple generations.
4. He identified and studied seven distinct traits, such as seed shape, flower colour, and plant height.
5. Mendel formulated two fundamental laws of inheritance: the Law of Segregation (alleles segregate during gamete formation) and the Law of Independent Assortment (traits assort independently during gamete formation).
6. He proposed the concept of dominant and recessive alleles, explaining how certain traits can be hidden in one generation and reappear in later generations.

Question 3

What are the reasons behind Mendel’s success?

Answer

Here are some of the reasons behind Mendel’s success:

• He chose the right organism to study. Pea plants are easy to grow and have a short generation time, which allowed Mendel to conduct many experiments in a relatively short period of time.
• He used a rigorous experimental method. Mendel carefully controlled his experiments and repeated them many times to ensure that his results were accurate.
• He was able to identify the key factors that influence inheritance. Mendel recognized that the traits he was studying were controlled by genes and that these genes were inherited in a particulate way.
• He was able to formulate two laws of inheritance that have stood the test of time. Mendel’s laws of segregation and independent assortment are the foundation of modern genetics.

Question 4

What are the seven characteristics of the pea plant? State their contrasting features in pea plant

Answer

Here are the contrasting features of the seven characters of the pea plant:

Question 5

Describe the hybridization technique which was carried out between plants having contrasting features in controlled conditions.

Answer

Here is a description of the hybridization technique that was carried out between plants having contrasting features in controlled conditions:

1. Choose two pea plants that have contrasting features for a particular trait. For example, one plant could be tall and the other plant could be short.
2. Fertilize the flowers of the tall plant with pollen from the short plant. This will create an F1 hybrid plant that has the tall allele from the tall plant and the short allele from the short plant.
3. Allow the F1 hybrid plant to self-pollinate. This will create an F2 generation of plants.
4. Observe the traits of the F2 generation. Mendel found that the F2 generation showed a 3:1 phenotypic ratio for the contrasting trait. This means that 3/4 of the plants in the F2 generation had the dominant phenotype and 1/4 of the plants had the recessive phenotype.

Question 6

What is the law of segregation? Describe the events of the monohybrid cross of the pea plant with checkerboards.

Answer

The law of segregation states that actors passed from one generation to another in an unaltered manner; they separate during gamete formation, reunite during fertilization and pass to the next generation.

Question 7

What is the explanation of a monohybrid cross?

Answer

A monohybrid cross is a cross between two organisms that differ in only one trait. This means that each parent carries one allele for the trait, either dominant or recessive. The offspring of a monohybrid cross will inherit one allele from each parent, and the possible combinations of alleles are:

• Homozygous dominant: The offspring will have two copies of the dominant allele, and will express the dominant phenotype.
• Heterozygous: The offspring will have one copy of the dominant allele and one copy of the recessive allele, and will express the dominant phenotype.
• Homozygous recessive: The offspring will have two copies of the recessive allele, and will express the recessive phenotype.

The phenotypic ratio of a monohybrid cross is 3:1, which means that there will be three offspring with the dominant phenotype and one offspring with the recessive phenotype.

Here is an example of a monohybrid cross:

• Parent 1: Homozygous dominant (TT)
• Parent 2: Homozygous recessive (tt)
• Offspring: 1/2 Tt (heterozygous) and 1/2 tt (homozygous recessive)
• Phenotypic ratio: 3:1 (dominant:recessive)

Question 8

What is the explanation of a dihybrid cross?

Answer

A dihybrid cross is a cross between two organisms that are heterozygous for two different traits. This means that each parent carries one dominant allele and one recessive allele for each trait. The offspring of a dihybrid cross will inherit one allele from each parent for each trait, and the possible combinations of alleles are:

• Dominant allele for both traits (DDYY)
• Dominant allele for the first trait and recessive allele for the second trait (DdYy)
• Recessive allele for the first trait and dominant allele for the second trait (ddYy)
• Recessive allele for both traits (ddyy)

The phenotypic ratio of a dihybrid cross is 9:3:3:1, which means that there will be:

• 9 offspring with the dominant phenotype for both traits (DDYY or DdYy)
• 3 offspring with the dominant phenotype for the first trait and the recessive phenotype for the second trait (DdYy)
• 3 offspring with the recessive phenotype for the first trait and the dominant phenotype for the second trait (ddYy)
• 1 offspring with the recessive phenotype for both traits (ddyy)

The genotypic ratio of a dihybrid cross is 1:2:2:4:1:2:1:2:1, which shows the different combinations of alleles that the offspring can inherit.

Question 9

What is a dihybrid cross? Describe the events of the dihybrid cross of plants 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.

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. The 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 the 9:3:3:1 ratio which is a dihybrid ratio.

Question 10

Describe the experiments of monohybrid cross in guinea pig with checkerboard.

Answer

Experiments of Monohybrid Cross in Guineapig: For the experiment of monohybrid cross in Guineapig, a homozygous black Guineapig (BB) is crossed with a homozygous white Guineapig (bb), then all hybrids of the first filial generation (Fx) are found to be black (Bb). From this, it is proved that black is dominant over white. As black is pure homozygous and dominant, its genotype will be BB and as white is pure homozygous but recessive, its genotype will be bb. BB will produce one type of gamete B. In F₁ the genotype will be Bb. The black hybrid of Fj when mated among themselves produces black and white offspring in 3 : 1 ratio i.e., 75% black and 25% white. Out of 75% black Guineapig 25% are pure black (BB), 50% are hybrid (heterozygous) black (Bb), and 25% are pure white (bb). So, the genotypic ratio becomes 1:2:1.

Question 11

What is the deviation from Mendel’s law of heredity?

Answer

Here are some of the deviations from Mendel’s law of heredity in short:

• Multiple alleles: A gene can have more than two alleles, which means that there are more than two possible phenotypes for that trait.
• Incomplete dominance: This is when the two alleles of a gene do not completely mask each other, resulting in a phenotype that is intermediate between the two.
• Codominance: This is when both alleles of a gene are expressed in the phenotype.
• Polygenic inheritance: This is when a single trait is controlled by multiple genes.
• Linkage: This is when two genes are located on the same chromosome and are therefore inherited together.

Question 12

What is the law of independent assortment? Briefly describe the event of a dihybrid cross in guinea pig with a checkerboard.

Answer

Independent assortment : 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).

Experiments of Dihybrid Cross In Guineapig: One homozygous female black Guineapig with rough hair (BBRR) was crossed with a male homozygous white Guineapig with smooth hair (bbrr). Black colour (B) is dominant over white (b) and rough hair (R) is dominant over smooth hair (r). All the offspring of the F₁ generation were black and rough (BbRr). When these F₁ male and female hybrids intercrossed (BbRr x BbRr) four types were obtained in F₂ generation. The following four types of Guineapig were produced in the F₂ generation. (i) 9/16 black and rough, (ii) 3/16 black and smooth, (iii) 3/16 white and rough, (iv) 1/16 white and smooth, their ratio was 9 : 3 : 3 : 1.

Question 13

Describe the sex determination of humans.

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 14

What is colourblindness? What are the symptoms of thalassemia?

Answer

Colour blindness, also known as colour vision deficiency, is a vision disorder where a person has difficulty perceiving certain colours.

Symptoms of thalassemia

• Fatigue.
• Shortness of breath.
• Pale skin.
• Yellowing of the skin and eyes (jaundice).

Question 15

Brief notes on thalassemia as an autosomal chromosomal disorder and its genetic counselling.

Answer

Thalassemia as an Autosomal Chromosomal Disorder:

Thalassemia is an autosomal chromosomal disorder that affects haemoglobin production, leading to abnormal red blood cells and anaemia. It can be alpha or beta thalassemia based on which globin chain is affected.

Genetic Counselling for Thalassemia:

Genetic counselling helps individuals or couples understand the risk of thalassemia based on family history and genetic testing. It offers carrier screening, reproductive options, family planning advice, and emotional support to make informed decisions about managing the condition and reducing the risk of passing it to future generations.

Question 16

Briefly state the types of colour blindness. Describe haemophilia in brief.

Answer

Types of Color Blindness:

1. Protanomaly: Reduced sensitivity to red light.
2. Deuteranomaly: Reduced sensitivity to green light.
3. Tritanomaly: Reduced sensitivity to blue light.
4. Protanopia: Absence of red cones.
5. Deuteranopia: Absence of green cones.
6. Tritanopia: Absence of blue cones.

Haemophilia: Haemophilia is a genetic bleeding disorder, usually X-linked, where the blood lacks certain clotting factors (usually factor VIII or IX). It leads to prolonged bleeding after injuries or surgeries and can cause internal bleeding without apparent trauma. It primarily affects males, while females are typically carriers. Treatment involves clotting factor replacement therapy.

Question 17

What is incomplete dominance? State about the incomplete dominance in the 4 O’clock plant.

Answer

Incomplete Dominance: Incomplete dominance is a genetic situation where neither allele is completely dominant over the other, resulting in an intermediate phenotype in heterozygous individuals.

Incomplete Dominance in 4 O’clock Plant: In the 4 O’clock plant (Mirabilis jalapa), the flower colour exhibits incomplete dominance. When a red-flowered (RR) plant is crossed with a white-flowered (WW) plant, the F1 generation (RW) displays pink flowers, showing an intermediate phenotype between red and white.

Question 18

What is the variation? Explain the two variable features in a man.

Answer

Variation: Variation refers to the differences observed among individuals within a population, resulting from genetic, environmental, or a combination of both factors.

Two-Variable Features in a Man:

1. Height: The height of a man can vary significantly based on genetic factors, nutrition, and overall health.
2. Eye Color: Men can have different eye colours, such as brown, blue, green, or grey, depending on the specific combination of genes inherited from their parents.

Question 19

Define mutation. State about the development of variation.

Answer

Question 20

State the phenotype and genotype with a sample cross. What is an allele?

Answer

Allele: An allele is a variant form of a gene, representing different versions of the same gene, and individuals inherit two alleles for each gene, one from each parent.

Sample Cross: In a cross between a smooth-seeded pea plant (SS) and a wrinkled-seeded pea plant (ss), the phenotype for seed texture is either “smooth” or “wrinkled.” The genotype possibilities for the offspring are SS (homozygous smooth) or Ss (heterozygous), all showing a smooth seed phenotype because the smooth allele is dominant over the wrinkled allele.