Question

Mitosis and Meiosis.

1. Draw a cell where 2n = 6 in each phase of Mitosis, Meiosis 1, and Meiosis 2. Be sure to clearly indicate what is going on with the 1-nuclear envelope, 2-centrosomes, 3-chromosomes in each of the stages.

2. For a diploid organism where 2n = 16, please indicate the number of chromosomes and chromatids at each of the Mitosis, Meiosis 1, Meiosis 2 stages.

Answer 1

For an organism with 2n=16, following are the chromosome/chromatid numbers at various stages of mitosis and meiosis:

Mitosis: Prophase - 16/16, Metaphase- 16/32, Anaphase-16/32, Telophase- 16/16 per daughter cell

Meiosis I: Prophase I- 16/16, Metaphase I- 16/32, Anaphase I-16/32, Telophase I- 8/8 per daughter cell

Meiosis II: Prophase II- 8/8, Metaphase II- 8/16, Anaphase II- 8/16, Telophase II- 8/8

From the above diagrams and calculations, it is clear that chromosome number of daughter cells is same as that of the parent cell during mitosis. however in meiosis I, each daughter cell recieves half the number of chromosomes, hence called reductional division. so the new daughter cells produced are haploid (n=3). Moreover there occurs exchange of chromosome segments between non-sister chromatids of homologous chromosomes (Crossing over) which leads to variations.