Suppose an Individual Is Heterozygous for Two Linked Pairs of Alleles

question 41

Multiple Choice

Suppose an individual is heterozygous for two linked pairs of alleles on the same chromosome arm,Ab/aB such that the A locus is closer to the centromere than the B locus.Under what conditions would a crossover in a somatic cell generate a twin spot,i.e. ,two adjacent clones of cells,one clone homozygous for a and the other clone homozygous for b?

• 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 B locus and involve two homologous (non-sister)chromatids.
• C) The crossover would have to occur between the B locus and the end of the chromosome locus and involve two homologous (non-sister)chromatids.
• D) A double crossover would have to occur,with one crossover between the A locus and the centromere and a second crossover between the A and B loci and both crossovers would have to involve two homologous (non-sister)chromatids.
• E) No crossover in a somatic cell could generate a twin spot.

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