A. Autosomal dominant.
B. Autosomal recessive.
C. X-linked dominant.
D. X-linked recessive.
The term “sex-linked recessive” most often refers to X-linked recessive.
- X-linked recessive diseases most often occur in males.
- Males have only one X chromosome. A single recessive gene on that X chromosome will cause the disease.
Sex-linked diseases are passed down through families through one of the X or Y chromosomes.
- Dominant inheritance occurs when an abnormal gene from one parent causes disease even though the matching gene from the other parent is normal. The abnormal gene dominates.
- But in recessive inheritance, both matching genes must be abnormal to cause disease.
- If only one gene in the pair is abnormal, the disease does not occur or it is mild.
- Someone who has one abnormal gene (but no symptoms) is called a carrier. Carriers can pass abnormal genes to their children.
- The Y chromosome is the other half of the XY gene pair in the male. However, the Y chromosome doesn’t contain most of the genes of the X chromosome.
- Because of that, it doesn’t protect the male. Diseases such as hemophilia and Duchenne muscular dystrophy occur from a recessive gene on the X chromosome.