Question

Recall that the fourth chromosome of Drosophila melanogaster does not recombine during meiosis. The lack of genetic polymorphism on this chromo- some has been interpreted as the product of a selec- tive sweep. If the fourth chromosome had normal rates of recombination, would you expect the level of polymorphism to be different? Why?

Answer 1

Normal recombination rates on the fourth chromosome of Drosophila melanogaster would likely increase genetic polymorphism due to more frequent new allele combinations and reduced effects of selective sweeps.

Step-by-step explanation:

If the fourth chromosome of Drosophila melanogaster had normal rates of recombination, we would expect to see a higher level of genetic polymorphism than currently observed. The lack of recombination on the fourth chromosome leads to less genetic diversity, as alleles are passed down in blocks rather than being shuffled through recombination events. Recombination is a key process that creates genetic diversity by exchanging DNA between homologous chromosomes during meiosis, as demonstrated in Curt Stern's and Barbara McClintock's studies. Without it, selective sweeps can have a more pronounced effect, purging variation from the population.

Therefore, with normal recombination rates, we would likely see an increased frequency of new allele combinations, which would result in greater genetic polymorphism on the fourth chromosome. This is due to both the production of new allele combinations through crossover events and a reduced likelihood of strong selective sweeps removing variation across large regions of the chromosome.