A patient is not certain whether she and her family should participate in a genetic screening plan

Question

She asks the nurse why the X-linked recessive disorder that has been noted in some of her family members is expressed in males more frequently than in females. What is the nurse's best response?
a. "The disease tends to show up in males because they do not have a second X chromosome to balance the expression of the gene."
b. "One X chromosome of a pair is always inactive in females. This inactivity effectively negates the effects of the gene."
c. "Females are known to have more effective DNA repair mechanisms than males, thus negating the damage caused by the recessive gene."
d. "Expression of genes from the male's Y chromosome does not occur in females, so they are essentially immune to the effects of the gene."

Answer 1

ANS: 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 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 in 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. It is incorrect to say that one X chromosome of a pair is always inactive in females or that females have more effective DNA repair mechanisms than males. Also, it is not true that females can be immune to the effects of a gene, because genes from the male's Y chromosome are not expressed in females.