Question

Summary Questions

1. What major event happens just before prophase I but does not occur before prophase II?

2. How do the chromosomes of an anaphase cell of mitosis differ from those of an anaphase cell of meiosis I?

3. Which results in the change in chromosome number from diploid to haploid, meiosis I or

       meiosis II?  

4. What is crossing over? Why is it significant?

5. Which process, mitosis or meiosis, produces daughter cells which are genetically identical to the parent cell? Explain.

Answer 1

Answer. Interphase occurs before prophase I but not before prophase II of meiosis,thus, chromosomes are reduced to half.

Answer 2. In anaphase I homologous chromosomes are separated from each other, by this each daughter receives half the number of chromosomes as that of the parent cell.

In anaphase II which is similar to mitotis anaphase, the sister chromatids are separated from each other, thus, the ploidy level is not changed.

Answer 3. Separation of homologous chromosomes in anaphase I makes the cell haploid, whereas separation of sister chromatids at anaphase II maintains the ploidy level of the cell. Means it will change it. In mitosis, the diploid ploidy is maintained by the division of sister chromatids at the anaphase, the departed chromatids then behave as chromosomes.

Answer 4. Crossing over refers to the exchange of genes between the paternal and maternal chromosomes at a point called chiasmata. This phenomenon occurs during the pachytene stage of prophase I, meiosis I.

It is because of the crossing over the offsprings show traits of both the parents. It also helps in bringing variation.

Answer 5. Mitosis produces the daughter cells exactly to that of the parent cell, even the ploidy level is maintained. Means from a diploid parent cell, two daughter cells will be formed which will be diploid only. In meiosis, at meiosis I the ploidy level is changed to haploid and meiosis II maintains the ploidy level.

Meiosis I will form two haploid cells. Now this each haploid cell will form two haploid cells by meiosis II which is same as mitosis. Thus, in meiosis from one diploid parent cell, four haploid daughter cells are formed.