Flg. 1. Breast cancer families 1 to 7. Solid circles, females with breast cancer; open circles, fe- males without breast cancer; open squares, males without breast cancer. The age given for each woman is age at (first) breast can- cer diagnosis (dx) if affected, age at death if deceased (deceased in- dividuals are represented by diag- onal lines through symbols), or age at most recent interview if alive without breast cancer. AlI- leles of D17S74 are shown for all families and are lettered sequen-
If the granddaughter III-1, has a girl, what is the chance that the girl will have the allele for breast cancer?
Answer:-
An allele is the alternative and variant form of a gene, which is located on the same locus. It contributes to the phenotype of the organism. The allele is responsible for the phenotype based on whether it is dominant or recessive.
It is given that a female acquires an X-linked dominant mutation.
None of her parents carry the mutation. So, she must be heterozygous for the dominant mutant allele.
XD = Dominant mutant allele
Xd = WT recessive allele Genotype of the woman = XDXd Genotype of the normal man = XdY Parental cross: XDXd X XdY
Progeny: XDXd XDY XdXd XdY
The probability that her daughter is affected = 1/2
= 50%
The chance that girl will have to the allele breast cancer is 50 %.
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