X-linked recessive

Definition

X-linked recessive refers to a mode of inheritance where a gene causing a trait or disorder is located on the X chromosome, and the expression of this trait occurs primarily in males. Since males have only one X chromosome, a single recessive allele on that chromosome can result in the manifestation of the associated trait or disorder. In females, who have two X chromosomes, two copies of the recessive allele are needed for the trait to be expressed, making them carriers if they have only one copy.

5 Must Know Facts For Your Next Test

1. X-linked recessive disorders are more commonly expressed in males due to their single X chromosome, which makes them more susceptible to these conditions.
2. Common examples of X-linked recessive disorders include hemophilia and Duchenne muscular dystrophy.
3. Females with one affected X chromosome are typically carriers and do not show symptoms unless they inherit a second affected X chromosome.
4. In pedigree analysis, affected males cannot pass the trait to their sons, but all daughters will be carriers if their father is affected.
5. The probability of a son inheriting an X-linked recessive disorder from a carrier mother is 50%, while daughters have a 50% chance of being carriers.

Review Questions

• How does the inheritance pattern of x-linked recessive traits affect males and females differently?
  • The inheritance pattern of x-linked recessive traits causes significant differences between males and females. Males, having only one X chromosome, will express the trait if they inherit just one recessive allele. In contrast, females have two X chromosomes, so they need two copies of the recessive allele to express the trait. This means females can be carriers without showing symptoms, while males are more likely to be affected by such disorders.
• In what ways can pedigree analysis assist in understanding the transmission of x-linked recessive traits within families?
  • Pedigree analysis is crucial for visualizing how x-linked recessive traits are passed through generations within families. By mapping out family members' phenotypes and genotypes, it helps identify carriers and predict how traits will be inherited. For instance, it reveals that affected males cannot pass the trait to their sons but will pass it to all daughters, showing the pattern of inheritance that could influence future offspring.
• Evaluate the implications of being a carrier for an x-linked recessive disorder on genetic counseling and family planning.
  • Being a carrier for an x-linked recessive disorder has important implications for genetic counseling and family planning. Carriers may not show symptoms but can pass on the gene to their children, making it essential for couples to understand their genetic backgrounds. Genetic counselors can provide information on the risks for each pregnancy based on carrier status and offer testing options for identifying carriers among family members. This understanding helps families make informed decisions regarding future offspring and management strategies.

Related terms

Hemizygous: Describes males who possess only one copy of the X chromosome, meaning they only express the genes on that X chromosome without a corresponding allele on a second X.

Carrier: An individual, usually female in the case of X-linked recessive traits, who has one copy of a recessive allele and does not express the trait but can pass it on to offspring.

Pedigree Analysis: A diagrammatic method used to track inheritance patterns of specific traits or disorders across generations in families, which can help identify carriers and predict probabilities of inheritance.