Question

In: Biology

Hemophilia is a sex-linked recessive disorder. If an unaffected woman mates with an unaffected man, and...


Hemophilia is a sex-linked recessive disorder. If an unaffected woman mates with an unaffected man, and they have 2 children with hemophilia, and 2 children who are unaffected,

What are the chances that the couple will have a girl who does not have hemophilia?

Solutions

Expert Solution

Hemophilia is a sex-linked recessive genetic disorder in humans. This means that a female will be affected only if she is homozygous for the allele and a male will be affected even when a single copy of the allele is present. Thus, according to the information, the genotype of the parents would be given by:

Mother: Unaffected (XhX)

Father: Unaffected (XY)

Here, two of the children are affected wheres other two are not. This can be possible only when the two affected children are inheriting two alleles each from a parent if they are females, or one allele from the mother if they are males. This, in turn, suggests that the mother should be a carrier for the disease but not affected herself.

Thus, the Punnett square for this couple can be formulated as below:

Xh X
X XXh XX
Y XhY XY

Genotype: XhX : XX: XhY: XY

Phenotype: Affected : Normal carriers: normal non-carriers :: 1 : 1: 2 or Affected : Normal :: 1:3

Thus, the chances of having an unaffected female child for this couple are 2/4 or 1/2 or 50%.


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