Why are X-linked recessive disorders expressed in males more frequently than in females?
A. Hemizygous traits in males have homozygous expression.
B. One X chromosome of a pair is always inactive in females.
C. Females have more effective DNA repair mechanisms than males.
D. Expression of genes from the Y chromosome does not occur among females.
A
Because the number of X chromosomes in males and females is not the same (1:2), the number of X-linked chromosome genes in the two genders is also unequal. Males have only one X chromosome, a condition called hemizygosity, for any gene on the X chromosome. As a result, X-linked recessive genes have a dominant expressive pattern of inheritance in males and a recessive expressive pattern of inheritance females. This difference in expression occurs because males do not have a second X chromosome to balance the expression of any recessive gene on the first X chromosome.
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