Question

In fruit flies, red eyes are dominant to green eyes. In a cross between a short-winged, green-eyed fly and a long-winged, red-eyed fly, the results were as follows:

40 percent short-winged and red-eyed
10 percent short-winged and green-eyed
10 percent long-winged and red-eyed
40 percent long-winged and green-eyed
The chromosome makeup of parents is reflected by

• A. $LlRr\times Llrr$
• B. $Llrr\times llrr$
• C. $LlRr\times llrr$
• D. $LLRR\times llrr$
• E. $LlRR\times llRr$

Answer 1

The correct option is C $LlRr\times llrr$

Since red eye color is dominant over green and long wings are dominant over short, the parents are homozygous for these recessive traits. The genotype of a parent with short-winged, green-eye is llrr and that of a long-winged, red-eyed fly is LlRr. The ratio of red and green-eyed progeny is 1:1 and likewise, the ratio of progeny with short and long wings is also 1:1. A cross between heterozygous dominant and homozygous recessive gives 1 dominant: 1 recessive progeny. This means the parent fly with long-wings, red-eyes is heterozygous for eye color and wing length. Therefore, the genotype of a parent with long-wings, red-eye is LlRr. Thus, the correct answer is option C.