The gene frequency for an X-linked recessive disease is 1 in 1,000 in the general population. What is the frequency of affected males in this population?
**Core Concept**
The problem involves understanding the genetics of X-linked recessive diseases, specifically how the frequency of the disease allele in the population relates to the frequency of affected males. X-linked recessive diseases are caused by mutations in genes on the X chromosome.
**Why the Correct Answer is Right**
Since the disease is X-linked recessive, males have only one X chromosome. Therefore, if a male inherits the disease allele, he will be affected. The frequency of affected males directly corresponds to the frequency of the disease allele in the population, as each male has only one X chromosome to contribute to the phenotype.
**Why Each Wrong Option is Incorrect**
**Option A:** This option might be considered if the disease were autosomal recessive, requiring two copies of the allele to express the disease.
**Option B:** This choice does not apply because it does not correctly represent the relationship between allele frequency and disease expression in X-linked recessive conditions.
**Option C:** Similar to Option A, this option does not correctly account for the X-linked nature of the disease.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that for X-linked recessive diseases, the frequency of affected males in the population is equal to the frequency of the disease allele, because males are hemizygous for X-linked genes.
**Correct Answer:** C. 1 in 1,000