X-linked recessive

Definition

X-linked recessive refers to a mode of inheritance where a mutation in a gene on the X chromosome leads to the expression of a trait or disorder primarily in males, as they have only one X chromosome. In this inheritance pattern, females with one mutated gene are typically carriers and may not show symptoms, whereas males who inherit the mutated gene will express the trait or disorder due to the lack of a second X chromosome to mask it.

5 Must Know Facts For Your Next Test

1. X-linked recessive traits are often more common in males because they have only one X chromosome, while females have two X chromosomes that can mask the effect of the mutated gene.
2. Examples of disorders inherited in an X-linked recessive manner include Duchenne muscular dystrophy and color blindness, in addition to hemophilia.
3. A father cannot pass an X-linked recessive trait to his son, since sons inherit their Y chromosome from their father, while daughters inherit their father's single X chromosome.
4. Mothers who are carriers of an X-linked recessive trait have a 50% chance of passing the mutated gene to each child, with sons expressing the trait and daughters being carriers.
5. If a female inherits two copies of the mutated gene (one from each parent), she will express the condition, which is less common due to the rarity of such occurrences.

Review Questions

• How does being male or female affect the expression of X-linked recessive traits?
  • Being male significantly increases the likelihood of expressing X-linked recessive traits because males have only one X chromosome. If that X chromosome carries a mutation, there is no second X chromosome to potentially mask the effect. In contrast, females have two X chromosomes; if one carries a mutation, the other can often compensate for it, allowing many females to be carriers without showing symptoms.
• Discuss how family history and genetics play a role in determining whether an individual is affected by or a carrier of an X-linked recessive condition.
  • Family history is crucial in determining whether an individual might be affected by or a carrier of an X-linked recessive condition. If there are known cases of such conditions in a family, particularly affecting males, this suggests that there could be a carrier female in the lineage. Genetic testing can provide insights into whether individuals carry mutations on their X chromosomes, helping assess risks for future generations.
• Evaluate the implications of X-linked recessive inheritance patterns for genetic counseling and family planning.
  • The implications of X-linked recessive inheritance patterns for genetic counseling are significant, particularly for families with a history of such conditions. Counselors can provide tailored advice on risks for offspring based on parental genotypes, especially for carrier mothers. Understanding these patterns allows families to make informed decisions about family planning and can guide them in choosing testing options for potential carriers or affected individuals within the family.

Related terms

Chromosome: A thread-like structure made of DNA and protein that carries genetic information. Humans have 23 pairs of chromosomes, including one pair of sex chromosomes (XX for females and XY for males).

Carrier: An individual who has one copy of a mutated gene but does not exhibit symptoms of the associated disorder. Carriers can pass the mutated gene to their offspring.

Hemophilia: A genetic disorder that impairs the body’s ability to make blood clots, often resulting in excessive bleeding. It is an example of an X-linked recessive condition.