Question

Meiosis creates 4 gametes. In females, only 1 of those gametes is an egg (the other 3 are "polar bodies"). If crossing over never occurs, what is the probability that two eggs produced by a 2n=46 human are genetically identical (except for mutation)? or two eggs produced by a 2n=4 female are genetically identical (except for mutation)? Explain your reasoning for the 2n=46 scenario.

Answer 1

Ans. Crossing over involves exchange the chromosomal segments between homologous chromosomes resulting in recombinant gametes (egg or sperms). If crossing over does not occur there will be no genetic recombination and hence recombinant gemetes will not be produced. Without crossing over it leads to production of genetically identical gametes. Out of the four cells resulted without crossing over during gamete formation, two cells are identical genetically and other two cells are identical genetically. In case of 2n=46, cells produced would have n=23 (haploid) without genetic recombination and it is the same as the case of mitosis (involves separation of chromatids of a chromosome without crossing over) Hence,the probability of two eggs is 50% (out of 4 cells two are identical).