In a cross between a white-eyed female fruit fly and red-eyed male, what percent of the female offspring will have white eyes? (White eyes are X-linked, recessive)
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To determine the percentage of female offspring with white eyes in a cross between a white-eyed female fruit fly (XwXw) and a red-eyed male (XwY), we need to consider the inheritance pattern of the white eye color.
In fruit flies, eye color is determined by genes located on the sex chromosomes - X and Y. The white eye color is X-linked recessive, meaning it is carried on the X chromosome. Since the white-eyed female is homozygous for white eyes (XwXw), all her eggs will carry the white-eye allele (Xw).
When the eggs from the white-eyed female are fertilized by the red-eyed male sperm (XwY), the possible genotypes of the female offspring are as follows:
1. XwXw: Female offspring inheriting the Xw chromosome from the mother and a Y chromosome from the father will have white eyes.
2. XwX: Female offspring inheriting the Xw chromosome from the mother and a normal X chromosome from the father will have red eyes.
Since the white-eyed female is homozygous for the white eye allele (XwXw), all her male offspring will have red eyes because they will receive the Y chromosome from the father. However, all the female offspring will inherit the X chromosome from the mother, which can be either XwXw or XwX.
Therefore, 100% of the female offspring from the cross between a white-eyed female fruit fly and a red-eyed male will have at least one white eye allele.
To determine the percentage of female offspring with white eyes in a cross between a white-eyed female fruit fly and a red-eyed male, we need to understand the inheritance pattern of the white eye trait.
In fruit flies, eye color is linked to sex chromosomes, where the white eye trait is X-linked recessive. This means that the gene responsible for white eyes is located on the X chromosome, and it requires two copies of the recessive allele (one from each parent) for the female offspring to have white eyes.
Let's break down the possible genetic combinations for the offspring:
1. Female offspring inheriting a white eye allele from both parents (XwXw): These females will have white eyes.
2. Female offspring inheriting a red eye allele from the male parent and a white eye allele from the female parent (XRXw): These females will have red eyes since the red eye allele is dominant over the white eye allele.
3. Female offspring inheriting a red eye allele from both parents (XRXR): These females will have red eyes.
Since only the females that inherit two white eye alleles (XwXw) will have white eyes, we need to determine the probability of this specific combination occurring.
The white-eyed female parent is guaranteed to have two white eye alleles (XwXw) because the trait is recessive in her case. On the other hand, the male parent has red eyes, so he must have the dominant red eye allele (XRXR).
When these parents are crossed, we can expect that each female offspring has a 50% chance of inheriting the white eye allele (Xw) from the mother and a 50% chance of inheriting the red eye allele (XR) from the father.
Since these events are independent, we can multiply the probabilities:
- The probability of inheriting the white eye allele from the mother is 0.5 (50%).
- The probability of inheriting the red eye allele from the father is 1 (100%) because he only carries the red eye allele.
Multiplying these probabilities, we find that the chance of a female offspring having two white eye alleles (XwXw) is 0.5 * 1 = 0.5 (or 50%).
Therefore, in this cross, 50% of the female offspring will have white eyes.