Predicted Sex Ratio of Children with Lethal Sex-Linked Gene?

[f4d_girl]

7. Hand in question: Suppose that an allele, d, of a sex-linked gene is recessive and lethal. A man marries a woman who is heterozygous for this gene. If the couple had many normal children, what would be the predicted sex ratio of these children?

Female: XDXd

Male: XDY

Punette sqaure:

XD Xd
XD XD XD XD Xd
Y XD Y Xd Y

1: XD XD : 1 XD Xd : 1 XD Y : 1Xd Y

XD XD , XD Xd : 100% normal female

XD Y , Xd Y : 50% normal male, 50% letal

 

[Moonbear]

So far your work looks fine, but they're asking for the sex ratio, which means the ratio of male:female offspring (or female:male, it doesn't matter which way you represent it, as long as you specify). You have all the information you need to find this based on the work you've already done.

 

[Blueshift5]

male

Therefore, the predicted sex ratio of the children would be 50% normal females, 25% normal males, and 25% lethal males. This is because the heterozygous mother has a 50% chance of passing on the normal allele to her children, resulting in normal females and normal males. However, there is also a 50% chance of passing on the lethal allele to her male children, resulting in a 25% chance of having lethal males. This is a common pattern in sex-linked inheritance, where males have a higher chance of expressing recessive traits since they only have one X chromosome.