Chapter 19, Problem 45A

Summary Introduction

To analyze:

Ways by which meiosis leads to genetic variation.

Introduction:

Germ cells i.e. sperm and ovum divide by meiosis. Two cycles of division give rise to 4 daughter cells with haploid chromosomes (n). All the daughter cells contain half the information inherited from the father and the other information is inherited from the mother. This type of division is characteristic of sexually reproducing organisms.

Explanation of Solution

Meiosis is known to play an important role in providing genetic variety.

The first source of variation arises when the gametes having a slight difference in genotypes are crossed during fertilization in parental gametes.

The second source of variation is an independent assortment that takes place during metaphase I. In this phase, chromosomes from mother and father align themselves at the equator and independently assort giving sister chromatids to be dispersed from each parent in a random manner.

The third source of variation occurs when the phenomenon of crossing over happens. The first time it happens in metaphase I during which the exchange of genetic material between the homologous chromosomes takes place. The other time it happens is in the prophase 1 of meiosis where the exchange of material and hence genetic information between the homologous pair of chromosomes happens.

Conclusion

Time of fertilization, independent assortment, and crossing over are the processes during meiosis that lead to genetic variations among individuals of the same species.