what ratio of offspring would result from a cross between a white-eyed male and a female that is heterozygous for red eye color?

Answer 1

To analyze the cross between a white-eyed male and a heterozygous female for red eye color in Drosophila melanogaster (fruit flies), we first need to define the alleles involved.

• Let \( R \) represent the allele for red eyes (dominant).
• Let \( r \) represent the allele for white eyes (recessive).

In this case:

• The white-eyed male has the genotype \( rY \) (because males have only one X chromosome).
• The heterozygous female has the genotype \( Rr \).

Now, let’s set up the Punnett square for their offspring:

1. Male (rY) gametes: \( r \) and \( Y \)
2. Female (Rr) gametes: \( R \) and \( r \)

The possible combinations from the Punnett square would be:

| | R | r | |---------|---------|---------| | r | Rr | rr | | Y | RY | rY |

From this Punnett square, we can see the resulting genotypes of the offspring:

1. \( Rr \) - Red eyes (heterozygous)
2. \( rr \) - White eyes (homozygous recessive)
3. \( RY \) - Red eyes (hemizygous male)
4. \( rY \) - White eyes (hemizygous male)

Counting the results:

• \( Rr \) - 1 (red-eyed female)
• \( rr \) - 1 (white-eyed female)
• \( RY \) - 1 (red-eyed male)
• \( rY \) - 1 (white-eyed male)

Thus, the offspring's phenotypic ratio would be:

• Red-eyed: \( 2 \) (1 \( Rr \) female + 1 \( RY \) male)
• White-eyed: \( 2 \) (1 \( rr \) female + 1 \( rY \) male)

The ratio of red-eyed to white-eyed offspring would therefore be 2:2, which simplifies to 1:1.