In fruit flies, eye colour is a sex-linked trait. Red eyes are dominant over white eyes.
If a white-eyed female fly is crossed with a red-eyed male fly, what proportion of the offspring would have white eyes?
A) 0%
B) 25%
C) 50%
D) 75%
Actually I think I got it, 1:1 - 50%
sdfs
To determine the proportion of offspring with white eyes, we need to know the genotypes of the parent flies. Since white eyes are a recessive trait and red eyes are dominant, we can deduce the genotypes as follows:
- The white-eyed female fly must be homozygous for the recessive allele: ww.
- The red-eyed male fly could be either homozygous for the dominant allele: RR or heterozygous: Rr.
When we cross these two flies, the possible genotypes of the offspring will be:
- 100% of the offspring will inherit one recessive allele from the white-eyed female (ww).
- If the red-eyed male is homozygous dominant (RR), then all the offspring will inherit one dominant allele from the male (R) and one recessive allele from the female (w). The genotype will be Rr, meaning they will have red eyes.
- If the red-eyed male is heterozygous (Rr), then 50% of the offspring will inherit the dominant allele from the male (R) and the recessive allele from the female (w). The genotype will be Rr, meaning they will have red eyes. The other 50% will inherit the recessive allele from both parents (ww), resulting in white eyes.
Therefore, the proportion of offspring with white eyes would be:
- If the red-eyed male is homozygous dominant (RR): 0%
- If the red-eyed male is heterozygous (Rr): 50%
Based on these possibilities, the answer is (B) 25%.
To determine the proportion of offspring with white eyes in this cross, we need to consider the specific inheritance pattern for eye color in fruit flies. In this case, eye color is a sex-linked trait, meaning that it is determined by genes located on the sex chromosomes.
In fruit flies, females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The gene for eye color is located on the X chromosome.
When a white-eyed female fly (XX) is crossed with a red-eyed male fly (XY), the possible combinations of sex chromosomes in the offspring are:
1. X from the mother (white-eyed female) and X from the father (red-eyed male): These offspring will have red eyes.
2. X from the mother (white-eyed female) and Y from the father (red-eyed male): These offspring will have white eyes.
Therefore, 50% of the offspring will have white eyes.
The correct answer is C) 50%.