As with autosomal traits, you can utilize the Punnett square to study the transmission of sex-linked traits. When completing these crosses, the gametes identify the sex chromosomes only. The genes located on the X chromosome are indicated with superscript letters. (We will not examine any cases where we track a Y-linked gene.) As with Mendelian traits, a lowercase letter indicates a recessive allele, while an uppercase letter indicates a dominant allele. When discussing sex-linked traits, carriers (females who are heterozygous for a recessive trait) need to be considered. Figure 5 illustrates several examples of genetic crosses involving sex-linked traits. White boxes represent unaffected individuals, light-colored boxes represent carriers, and dark-colored boxes represent affected individuals.
Transcript for Sex Chromosomes - Part I