Multiple choice

Two genes are located on the same chromosome and are known to be 12 map units apart. An AABB individual is crossed to an aabb individual to produce AaBb offspring. The AaBb offsprings are then crossed to aabb individuals. If this cross produces 1000 offsprings, what is the predicted number of offsprings with each of the four genotypes: AaBb, Aabb, aaBb and aabb?

  1. 60 Aabb, 440 aaBb, 440 AaBb and 60 aabb

  2. 0 Aabb, 0 aaBb, 440 AaBb and 440 aabb

  3. 440 Aabb, 440 aaBb, 60 AaBb and 60 aabb

  4. 60 Aabb, 60 aaBb, 440 AaBb and 440 aabb
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The genes are 12 map units apart, so the recombination frequency is 12%. Parental gametes (AB and ab) occur 88% of the time (44% each), while recombinant gametes (Ab and aB) occur 12% of the time (6% each). When AaBb is crossed with aabb, we get 440 AaBb, 440 aabb, 60 Aabb, and 60 aaBb.

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