In fruit flies, the color of the eyes is sex linked (on the X chromosome). Complete the cross of the flies in the image to determine the possible offspring produced. (Homozygous white eyed female x red eyed male) Red eyes are dominant (R), White eyes are recessive (r). What percentage of the male offspring are expected to have red eyes? a 100% b 75% c 50% d 25% e 0%

Answer 1

To determine the percentage of male offspring that will have red eyes from the cross of a homozygous white-eyed female and a red-eyed male, let's set up the genotypes:

• The genotype of the homozygous white-eyed female is X^rX^r (both X chromosomes carry the recessive allele for white eyes).
• The genotype of the red-eyed male is X^RY (one X chromosome carrying the dominant allele for red eyes and a Y chromosome).

When we perform the genetic cross, we can create a Punnett square to visualize the offspring’s possible genotypes:

     X^R       Y
   ----------------
X^r | X^rX^R  | X^rY  |
   ----------------
X^r | X^rX^R  | X^rY  |
   ----------------

From the Punnett square, the possible genotypes of the offspring are:

• X^rX^R (female with red eyes) - 50%
• X^rY (male with white eyes) - 50%

Since the question specifically asks for the percentage of male offspring that are expected to have red eyes, we can see that:

• All male offspring in this cross (X^rY) will have white eyes.

Thus, the answer is e 0%. None of the male offspring are expected to have red eyes.