OpenStudy (anonymous):

Hemophilia is an x-linked recessive disease. Under which of the following conditions will a female child inherit hemophilia? Both parents must have the hemophilia allele. Only the father must have the hemophilia allele. Both sets of grandparents must have the hemophilia allele. Only the mother must have the hemophilia allele.

5 years ago
OpenStudy (anonymous):

Since hemophilia is x-linked, that means the disease allele will always be on an X chromosome, and since the disease is a recessive trait, then one normal X chromosome will "cover up" the effects of the disease allele on another X chromosome, if another X chromosome is present. Females have two X chromosomes, so to show symptoms of hemophilia, both of their X chromosomes need to be recessive (carry the hemophilia allele). Since a female inherits one X chromosome from her father and one from her mother, both parents must have at least one hemophilia allele. (Note that the father has only one X chromosome to be passed on to his daughter, so that chromosome must have the diseased allele, and the father must be affected with hemophilia.)

5 years ago
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