In Drosophila , straight wings are dominant to curved wings ( c ), smooth eyes a
ID: 32661 • Letter: I
Question
In Drosophila, straight wings are dominant to curved wings (c), smooth eyes are dominant to sparkling eyes (spa), and tan body is dominant to ebony body color (e).
Part A
If flies that are heterozygous for all three traits are crossed, what proportion of the offspring would you expect to be heterozygous for all three traits?
Part B
If flies that are heterozygous for all three traits are crossed, what proportion of the offspring would you expect to have straight wings, sparkling eyes, and tan bodies?
Part C
If flies that are heterozygous for all three traits are crossed with flies that are homozygous recessive for all three traits, what proportion of the offspring would you expect to be heterozygous for all three traits?
Express your answer as a fraction.
Explanation / Answer
a. If both of the parents are heterozygous, then 50% of their offspring will be heterozygous for just one trait. For three traits, you just need to cube the value of 0.5 to find out the percentage. (0.5)^3 = 0.125 or 1/8. So 1/8 of the the offspring will be heterozygous.
b. In this case, the offspring will have two dominant traits and one recessive trait. If One of the Alleles for a traight is dominant, then the expressed traight will be dominant, assuming there is no mixing of traits. So for any offspring with these traits, they can have one or both domiant alleles for the wing shape and body color traits, but they must have both recessive alleles for the eye trait. Using a punnett square, you can find the number, which happens to be 9/64.
c. Using a punnett square you can also find this value, which in this case is 1/8
http://scienceprimer.com/punnett-square-calculator
This website is very useful for what you're doing. I know I didn't draw out the punnet squares out for you but the calclator from this website is very easy to use, you can set it up the way you want and simply copy the punnet square to show your work.