Image Based Question – 66357

Identify the type of inheritance shown in the photograph below ?

A. Autosomal dominant.

B. Autosomal recessive.

C. X-linked dominant.

D. X-linked recessive.

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Correct Answer » D Explanation

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.