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Multiple Choice
In sex-linked inheritance, what genotype must a female have to express the genetic disease hemophilia?
A
XHXH
B
XhY
C
XHXh
D
XhXh
Verified step by step guidance
1
Understand that hemophilia is a sex-linked genetic disorder, which means it is associated with genes located on the sex chromosomes, specifically the X chromosome.
Recognize that females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
Identify that hemophilia is a recessive disorder, meaning that the disease manifests only when there are two copies of the recessive allele present.
For a female to express hemophilia, she must have two copies of the recessive allele on both of her X chromosomes. This means her genotype must be XhXh, where 'Xh' represents the X chromosome carrying the hemophilia allele.
Compare the given genotypes: XHXH (homozygous dominant, does not express hemophilia), XhY (male genotype, not applicable to females), XHXh (heterozygous, carrier but does not express hemophilia), and XhXh (homozygous recessive, expresses hemophilia). The correct genotype for a female expressing hemophilia is XhXh.