Q.Differentiate between mitosis and meiosis

Mitosis is a single, equational division producing two genetically identical diploid cells for growth/repair; meiosis is a two-step, reductional division producing four genetically distinct haploid gametes for sexual reproduction.

(a) Difference between mitosis and meiosis (answering the primary part of this question):

1. Site of occurrence: Mitosis occurs in somatic (body) cells (and in some organisms, in cells destined for asexual reproduction). Meiosis occurs only in germ cells / cells destined to become gametes, in reproductive organs.

2. Number of divisions: Mitosis involves a single division of the nucleus and cytoplasm. Meiosis involves two successive divisions — meiosis I and meiosis II — occurring one after the other.

3. Number and ploidy of daughter cells: Mitosis produces 2 daughter cells, each diploid (2n), with the same chromosome number as the parent cell. Meiosis produces 4 daughter cells, each haploid (n), with exactly half the chromosome number of the parent cell.

4. Genetic identity: The daughter cells from mitosis are genetically identical to the parent cell and to each other (barring rare mutation). The daughter cells from meiosis are genetically variable, both from the parent cell and from each other, due to crossing over and independent assortment.

5. Crossing over/synapsis: Mitosis does not involve pairing of homologous chromosomes or crossing over. Meiosis (specifically prophase I) involves synapsis of homologous chromosomes and crossing over between non-sister chromatids, which is the major source of genetic recombination.

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