A nurse is educating a client about genetic screening. The client ...

[iveyjurea]

A nurse is educating a client about genetic screening. The client asks why red-green color blindness, an X-linked recessive disorder noted in some of her family members, is expressed more frequently in males than females. How should the nurse respond?
 
  a. Females have a decreased penetrance rate for this gene mutation and are therefore less likely to express the trait.
  b. Females have two X chromosomes and one is always inactive. This inactivity decreases the effect of the gene.
  c. The incidence of X-linked recessive disorders is higher in males because they do not have a second X chromosome to balance expression of the gene.
  d. Males have only one X chromosome, which allows the X-linked recessive disorder to be transmitted from father to son.

Question 2

A client is typed and crossmatched for a unit of blood. Which statement by the nurse indicates a need for further genetic education?
 
  a. Blood type is formed from three gene alleles: A, B, and O.
  b. Each blood type allele is inherited from the mother or the father.
  c. If the client's blood type is AB, then the client is homozygous for that trait.
  d. If the client has a dominant and a recessive blood type allele, only the dominant will be expressed.

[sierramartinez]

Answer to Question 1

ANS: C
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 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 a decreased penetrance rate for this gene mutation. X-linked recessive disorders cannot be transmitted from father to son, but the trait is transmitted from father to all daughters who will be carriers.

Answer to Question 2

ANS: C
There are three possible gene alleles: A, B, and O. Blood type is determined by only two of the three specific gene alleles. The blood type OO is homozygous in contrast to the blood type AB, which is heterozygous. In the blood type AO, the gene allele A is dominant and will be expressed as blood type A. It is true that each blood type allele is inherited from the mother or the father.

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