A genetic pedigree showing that only males are affected by a certain disorder is evidence of what type of inheritance?

The appearance of a genetic pedigree where only males are affected by a specific disorder suggests that the disorder is transmitted through genes located on the sex chromosomes, particularly the X chromosome. This mode of inheritance is known as sex-linked inheritance. In sex-linked disorders, traits or conditions often associated with genes on the X chromosome can manifest predominantly in males due to their having only one X chromosome.

Since males inherit their X chromosome from their mothers, if a mother carries a recessive allele for a disorder on her X chromosome, she may not express the disorder herself (if she has a normal copy of the gene on her other X chromosome) but can pass it to her son, who will express the condition because he does not have a second X chromosome to potentially mask the affected allele. This is in contrast to autosomal inheritance patterns, where both males and females have two copies of each gene, and a disorder would not be limited to one gender in such a fashion.