a. In Drosophila, crosses between F1 heterozygotes ofthe form A b / a B always yield the same ratio ofphenotypes in the F2 progeny regardless of the distance between the two genes (assuming completedominance for both autosomal genes). What is thisratio? Would this also be the case if the F1 heterozygotes were A B / a b? (Hint: Remember that inDrosophila, recombination does not take placeduring spermatogenesis.)b. If you intercrossed F1 heterozygotes of the formA b / a B in mice, the phenotypic ratio among the F2progeny would vary with the map distance betweenthe two genes. Is there a simple way to estimate themap distance based on the frequencies of the F2phenotypes, assuming rates of recombination areequal in males and females? Could you estimatemap distances in the same way if the mouse F1heterozygotes were A B / a b?
a. In Drosophila, crosses between F1 heterozygotes of
the form A b / a B always yield the same ratio of
phenotypes in the F2 progeny regardless of the distance between the two genes (assuming complete
dominance for both autosomal genes). What is this
ratio? Would this also be the case if the F1 heterozygotes were A B / a b? (Hint: Remember that in
Drosophila, recombination does not take place
during spermatogenesis.)
b. If you intercrossed F1 heterozygotes of the form
A b / a B in mice, the
progeny would vary with the map distance between
the two genes. Is there a simple way to estimate the
map distance based on the frequencies of the F2
phenotypes, assuming rates of recombination are
equal in males and females? Could you estimate
map distances in the same way if the mouse F1
heterozygotes were A B / a b?
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. If you intercrossed F1 heterozygotes of the form
A b / a B in mice, the
progeny would vary with the map distance between
the two genes. Is there a simple way to estimate the
map distance based on the frequencies of the F2
phenotypes, assuming rates of recombination are
equal in males and females? Could you estimate
map distances in the same way if the mouse F1
heterozygotes were A B / a b?