A normal human male cannot be heterozygous for an SNP in the X chromosome.

Question

Quizplus · Accepted Answer

This is because males only have one X chromosome, inherited from their mother, and therefore cannot have two different versions (alleles) of an SNP on that chromosome. They would either have the SNP or not have it. Heterozygosity refers to having two different alleles at a particular genetic locus, and this is only possible in individuals with two copies of the chromosome in question (e.g. females have two X chromosomes).

A Normal Human Male Cannot Be Heterozygous for an SNP