Does crossover between one pair of homologs affect the expected proportions of gametes genotypes
The correct answer and explanation is:
Crossover between one pair of homologous chromosomes can indeed affect the expected proportions of gamete genotypes, especially when considering genetic recombination. To understand this, it’s important to grasp the concept of crossing over, which occurs during meiosis, the process of cell division that produces gametes.
In meiosis, homologous chromosomes (one from each parent) pair up and exchange segments of their chromatids in a process known as “crossover.” This process leads to genetic recombination, which can shuffle the alleles present on the chromosomes. The result is that the gametes formed will not only contain the alleles inherited from each parent but also new combinations of alleles that were created through the crossover event.
When a crossover occurs between homologous chromosomes, it can produce new allele combinations that would not have been present if the chromosomes segregated independently. This recombination affects the genotype of the gametes because it alters the distribution of alleles among the gametes, which can change the proportions of the possible genotypes in the offspring. For example, without crossing over, a parent with two heterozygous alleles (AB) would only produce AB gametes. However, with crossover, the gametes could contain either the original AB combination or new recombinants like Ab or aB, changing the expected genetic outcomes.
The effect of crossover is especially noticeable when genes are located near each other on the same chromosome. The closer the genes are to each other, the less likely a crossover is to occur between them, meaning the parental allele combinations are more likely to be passed on. On the other hand, genes that are farther apart have a higher chance of recombination, which results in a wider variety of allele combinations in the gametes.