Question

How would you determine if a mutation is X-linked recessive from a pedigree analysis?

Answer 1

To determine if a mutation is X-linked recessive in pedigree analysis, look for more males affected than females, no male-to-male transmission, and the passing of the trait from carrier mothers to half of their sons. An example of such a trait is color blindness.

Step-by-step explanation:

To determine if a mutation is X-linked recessive from a pedigree analysis, we look for specific patterns. One such pattern is that the trait appears more frequently in males than females. This is because males have only one X chromosome, so a single recessive allele on the X chromosome will cause them to express the trait. Females, in contrast, would need two copies of the recessive allele, one on each of their two X chromosomes, to express the trait. If they have only one copy, they are typically carriers without showing any symptoms.

When analyzing a pedigree, look for instances where affected males have unaffected mothers, indicating that the trait is recessive. Additionally, affected males often have carrier mothers, and their daughters will have a 50 percent chance of being carriers. Furthermore, it is unlikely to see affected females unless their father is affected and their mother is either a carrier or affected. If a trait consistently passes from a carrier mother to half of her sons, it is likely X-linked recessive.

Key Indicators of X-linked Recessive Inheritance in Pedigrees:

• More males than females are affected by the trait.
• No male-to-male transmission of the trait occurs.
• Females who are carriers pass the trait to half of their sons and none or half of their daughters depending on the father’s genotype.

A classic example of an X-linked recessive trait is color blindness. To express this trait, males need only to inherit one copy of the recessive allele, whereas females must inherit two copies, one from each parent.

Answer 2

To determine if a mutation is X-linked recessive using pedigree analysis, look for patterns such as the trait being more common in males, female carriers not expressing the trait, and affected males passing the trait to all their daughters as carriers. Examples include color blindness and hemophilia.

Step-by-step explanation:

To determine if a mutation is X-linked recessive from a pedigree analysis, several key patterns must be observed in the pedigree chart:

• The trait is more common in males than in females. This is because males have only one X chromosome so a single recessive allele on the X chromosome will result in expression of the trait.
• Females may carry the trait without expressing it, as they have two X chromosomes and a dominant allele on one X can mask the recessive allele on the other X.
• For a female to express the trait, she must inherit two recessive alleles, one from each parent.
• If a male has the trait, he will pass the recessive allele to all his daughters, making them carriers, but not to his sons, as they get his Y chromosome.
• Males cannot be carriers of X-linked recessive traits; they either have the trait or they don't.
• Daughters who are carriers have a 50 percent chance of passing the recessive allele to their sons, which would result in the sons expressing the trait.

Examples of X-linked recessive traits include color blindness, hemophilia, and certain forms of muscular dystrophy. When analyzing a pedigree, look for these patterns to identify an X-linked recessive allele.

If a recessive X-linked allele is expressed in males, it's because they possess only one X chromosome. If a female is a carrier of a recessive X-linked trait like color blindness, her sons will have a 50 percent chance of being affected, and her daughters will have a 50 percent chance of being carriers.