In Morgan's experiments with Drosophila melanogaster, when two genes on the same chromosome are located very close to each other, what frequency of recombinant progeny is observed?
Answer and explanation
Correct answer: B. Very low recombinant frequency ()
- Step 1: T.H. Morgan mapped genes on the X chromosome of Drosophila (such as yellow body and white eyes).
- Step 2: He discovered that genes situated on the same chromosome do not assort independently if they are physically linked.
- Step 3: Genes situated close together show tight linkage with a very low frequency of crossing over, resulting in a high proportion of parental types and a low recombinant frequency (, e.g., for yellow and white).
Answer
Very low recombinant frequency ().
Why not the others: recombinant frequency occurs when genes are on separate chromosomes or far apart on the same chromosome; recombinant frequency is physically impossible; Zero variation contradicts the occurrence of occasional crossovers.
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