Question

question 49
what information in a pedigree would indicate a condition is likely sex - linked?
fifty percent of the individuals in the pedigree are affected.
two - thirds of the affected individuals have affected parents.
most of the affected individuals are males.
none of the affected individuals have unaffected parents.

Explanation:

Sex - linked conditions, especially X - linked recessive conditions, are more common in males. Males have one X chromosome (from the mother). If the X chromosome has a recessive allele for a sex - linked disorder, they will express the trait. Females have two X chromosomes. They need two copies of the recessive allele (one from each parent) to express the X - linked recessive trait. So, a higher proportion of affected males in a pedigree suggests a sex - linked condition.

• The first option ("Fifty percent of the individuals in the pedigree are affected") is too general and not specific to sex - linked inheritance. Many non - sex - linked (e.g., autosomal) inheritance patterns can also have 50% affected individuals (e.g., autosomal dominant with one affected parent).
• The second option ("Two - thirds of the affected individuals have affected parents") is more in line with dominant inheritance (autosomal or sex - linked). But it does not specifically point to sex - linked.
• The fourth option ("None of the affected individuals have unaffected parents") is characteristic of dominant inheritance (if it was recessive, two unaffected parents could have an affected child if they are carriers). But again, not specific to sex - linked.

Answer:

Most of the affected individuals are males.