X-linked recessive inheritance

X-linked_recessive_(2).svg

X-linked recessive inheritance is a mode of genetic inheritance by which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (who are necessarily hemizygous for the gene mutation because they have only one X chromosome) and in females who are homozygous for the gene mutation, see X-linked inheritance.

Mechanism

In X-linked recessive inheritance, the gene causing the trait or the disorder is located on the X chromosome. Males have one X and one Y chromosome (XY), while females have two X chromosomes (XX). Because males have only one X chromosome, a single recessive gene on that X chromosome will cause the disease. In contrast, females have two X chromosomes, so a mutation would have to occur in both copies of the gene to cause the disease. Females with one mutated gene are called carriers and usually do not show symptoms of the disease.

Examples of X-linked recessive disorders

Some well-known examples of X-linked recessive disorders include:

• Hemophilia A
• Duchenne muscular dystrophy
• Red-green color blindness
• G6PD deficiency

Inheritance Pattern

The inheritance pattern of X-linked recessive disorders can be summarized as follows:

• Affected males cannot pass the disorder to their sons (since they pass their Y chromosome to their sons), but all their daughters will be carriers.
• Carrier females have a 50% chance of passing the mutated gene to their sons (who will be affected) and a 50% chance of passing the mutated gene to their daughters (who will be carriers).

Diagnosis and Genetic Counseling

Diagnosis of X-linked recessive disorders often involves genetic testing and family history analysis. Genetic counseling is recommended for families with a history of X-linked recessive disorders to understand the risks and implications of the inheritance pattern.

See also

• Genetic disorder
• Autosomal recessive inheritance
• Autosomal dominant inheritance
• Y-linked inheritance