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Question

Distinguish between Mitosis and Meiosis on the basis of the following three aspects

  1. Site of occurrence
  2. Nature of division of chromosome
  3. Number of cells produced

Explain the following phenomena related to meiotic cell division

  1. Separation of chromosome and chromatid
  2. Crossing over

Or

Distinguish between the cytokinesis of plant cells with the cytokinesis of animal cells on the basis of the following aspects :

  1. Process
  2. Time of initiation
  3. Role of Golgi bodies

Establish the interrelationships among genes, DNA and chromosome.

WBBSE Class X Life Science 02 (a) Cell Division and Cell Cycle 05 Mark 2022

Answer

Distinguish between Mitosis and Meiosis on the following three aspects

Aspect Mitosis Meiosis
Site of occurrence Occurs in somatic (body) cells of plants and animals Occurs in reproductive or germ cells (testes, ovaries, spore mother cell)
Nature of division of chromosome Equational division (chromosome number remains same in daughter cells as parent) Reductional division (chromosome number is reduced to half in daughter cells)
Number of cells produced Two identical diploid daughter cells Four non-identical haploid daughter cells

Phenomena related to meiotic cell division

1. Separation of Chromosome and Chromatid

  • In Meiosis I, homologous chromosomes are separated which reduces the chromosome number by half in the gametes/spores.
  • In Meiosis II, the chromatids of each chromosome separate, similar to what happens in mitosis.

2. Crossing Over

Crossing over is the exchange of genetic material between non-sister chromatids of homologous chromosomes during Prophase I of meiosis. This process results in new genetic combinations and increases genetic variation among offspring.

Or

Differences between Cytokinesis of Plant Cells and Animal Cells

Aspect Plant Cell Cytokinesis Animal Cell Cytokinesis
Process Formation of a cell plate by fusion of vesicles at the centre, which later develops into a new cell wall (phragmoplast method) Formation of a cleavage furrow (constriction forms at the periphery and moves inward dividing the cell)
Time of initiation Begins during late telophase, generally after karyokinesis Begins in late anaphase or early telophase, often overlaps with end of nuclear division
Role of Golgi bodies Golgi vesicles collect at the equator and form the cell plate (which becomes the new cell wall) Golgi bodies do not play a direct role in animal cell cytokinesis

Interrelationship among Genes, DNA, and Chromosome

  • Chromosomes are the gene-bearing, nucleoprotein filaments found in the nucleus of cells. They are composed mostly of chromatin and carry genes arranged linearly.
  • DNA is the chemical substance that forms chromosomes and is structured as a double helix. DNA coils and folds to form chromatin reticulum, which condenses to create chromosomes.
  • Genes are specific segments of DNA that carry the information necessary for the synthesis of proteins and determine hereditary traits. Each gene occupies a definite position (locus) on a chromosome.
  • Thus, chromosomes are made up of DNA, and genes are functional segments of DNA located on chromosomes.

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