In fruit flies, the gene for eye color is sex-linked (X-chromosome) and red eye
ID: 7352 • Letter: I
Question
In fruit flies, the gene for eye color is sex-linked (X-chromosome) and red eye color is dominant over white. The gene for body color is an autosomal trait with gray dominant over black. A heterozygous red-eyed, pure-bred gray female mates with a heterozygous gray male who has red eyes. What is the probability that any of the offspring produced have he following traits? You must show your work (i.e. Punnett squares) to get credit.a. Red eyes
b. gray body
c. white eyed female
d. white eyes and heterozygous gray body
e. female and red eyed gray body
Explanation / Answer
*Eye Color (r=red eye trait, w=white eye trait. The female's contribution is shown in the vertical column and the male's in the horizontal column.)
Xr Yw
Xr XrXr XrYw
Xw XrXw XwYw
1/2 - females with red eyes
1/4 - males with red eyes
1/4 - males with white eyes
*Body Color (G=grey body trait, g=black body trait. The female's contribution is shown in the vertical column and the male's in the horizontal column.)
G g
G GG Gg
G GG Gg
All offspring will have grey bodies and as such the value for probability equation is 1.
1/2 will be homozygous and 1/2 will be herterozygous for the grey body trait.
a.) ¾ of all offspring will have red eyes (see first punnett square) .
b.) All offspring from this pairing will have grey bodies (see second punnett square).
c.) There is no chance of white eyed female offspring from this pairing (see first punnett square).
d.) 1/4 (probability of white eyed)* 1/2 (probability of heterozygous grey)= 1/8 probability of offspring being white eyed and heterozygous grey body (all of these offspring will be male). *This was derived by applying the product law of probability.
e.) 1/2 (probability of female with red eyes)* 1 (since all offspring will have grey bodies- and this question does not make a heterozygote/homozyote distinction- the probability is 1)= 1/2 probability of an offspring being female with red eyes and grey body. *This was derived by applying the product law of probability.