Multiple choice

If A/A/.B/B is crossed to the a/a.b/b, and the F1 is test crossed. What percent of the test cross progeny will be a/a.b/b if the two genes are P. unlinked Q. completely linked (no crossing over at all) R. 10 map units apart S. 24 map units apart

  1. P – 0%, Q – 0%, R – 38%, S – 45%

  2. P – 25%, Q – 50%, R – 45%, S – 38%

  3. P – 0%, Q – 25%, R – 45%, S – 38%

  4. P – 25%, Q – 0%, R – 38%, S – 45%
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

For test cross of AaBb: P (unlinked) - parental aabb is 1/4 (25%). Q (completely linked) - aabb requires no crossover, so 50% parental types. R (10 map units) - 10% recombinants, so aabb = 45% parental. S (24 map units) - 24% recombinants, so aabb = 38% parental. The further apart the genes, the more crossing over, so fewer parental aabb progeny.

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