The student now performs a test cross of F1 dihybrid females (RrLl) with rrll males. Of 1000 offspring: 470 red long, 30 red vestigial, 25 white long, 475 white vestigial. The 9:3:3:1 result earlier was consistent with independent assortment, but this test cross result is dramatically skewed.
Which conclusion is best supported?
- A
Red is sex-linked
- Bcheck_circle
The two genes are linked on the same chromosome with infrequent recombination
- C
Vestigial is dominant to long
- D
The genes assort independently
Explanation
Independent assortment in a test cross would produce 1:1:1:1 (about 250 each). The two parental classes (470 red-long and 475 white-vestigial) far outnumber the recombinants (30 + 25 = 55). Recombination frequency = 55/1000 = 5.5 cM, indicating linkage.