Sally is a 43-year-old mother of two who has gained 50 pounds over the past 5 years. she is 64 inches tall and weighs 180 pounds with a bmi of 30.8. her waist circumference is 37 inches. she acknowledges that she is not as physically active as she would like to be. she also notes how recent stresses in her life have affected her sleep and seem to have triggered her appetite for sweets and comfort foods. sally's father recently died from complications of type 2 diabetes, and her mother and sisters are overweight. sally says she is very motivated to "not get diabetes" and is disturbed that her recent physical exam revealed mildly elevated blood pressure, glucose, and cholesterol levels.

an individual’s sex (i.e., whether they are a male or female) is determined by the sex chromosomes. most people have two sex chromosomes, one that is inherited from their mother and one that is inherited from their father. typically, females have two x chromosomes (xx) and males have one x chromosome and one y chromosome (xy). conditions caused by changes (“mutations”) in genes located on the x chromosome are considered x-linked.

x-linked recessive inheritance

most x-linked conditions are recessive. this means that in a person with two x chromosomes (most females), both copies of a gene (i.e., one on each x chromosome) must have a change or mutation whereas in a person with one x chromosome (most males), only one copy of a gene must have a mutation. a female with a mutation in one copy of a gene on the x chromosome is said to be a “carrier” for an x-linked condition. a male with a mutation in a gene on the x chromosome is typically affected with the condition. because females have two copies of the x chromosome and males have only one x chromosome, x-linked recessive diseases are more common among males than females. however, x-linked recessive diseases can occur in both males and females.

for x-linked recessive disorders, an unaffected carrier mother who has a mutation in a gene on the x chromosome can transmit either the x chromosome with this mutation or a “normal” x chromosome to her children. if the father is unaffected, none of her daughters will be affected and all of her daughters will be unaffected—since they will inherit at least one normal x chromosome from their father. however, each daughter will have a 50% chance of being an unaffected carrier like her mother and a 50% chance of both x chromosomes being normal.

answer n81.2