Suppose an individual is heterozygous for a pair of alleles (e.g., A/a).Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)
A)The crossover would have to occur between the A locus and the centromere and involve two homologous (non-sister) chromatids.
B)The crossover would have to occur between the A locus and the end of the chromosome and involve two homologous (non-sister) chromatids.
C)The crossover would have to occur on the same chromosome arm as the A locus and involve two homologous (non-sister) chromatids.
D)The crossover would have to occur on the same chromosome as the A locus and involve two homologous (non-sister) chromatids.
E)The crossover would have to occur between the A locus and the centromere and involve two sister chromatids (not homologous) chromatids.

Question

Quizplus · Accepted Answer

In order for a clone of cells to be homozygous for a particular allele, the crossover must occur within the region between the locus and the centromere, involving two homologous (non-sister) chromatids. This allows for a recombinant chromosome that has lost the other allele and contains two copies of the allele of interest. Crossovers that occur on the same chromosome arm but not in this specific region may still result in recombinant chromosomes, but they will not result in the loss or gain of alleles that lead to homozygosity. Sister chromatids are identical copies and do not undergo crossing over. Crossovers between the locus and the end of the chromosome may or may not result in homozygosity, depending on whether the resulting recombinant chromosome is lost or retained during subsequent cell division.

Suppose an Individual Is Heterozygous for a Pair of Alleles