Which allele combination represents a male who has an X-linked recessive disorder?

Step 1: Define the Problem

Identify the genetic makeup of a male with an X-linked recessive disorder.

Step 2: Break Down the Problem

1. Understand the nature of X-linked recessive disorders.
2. Determine how these disorders are inherited in males.

Step 3: Apply Relevant Concepts

• X-linked Recessive Disorders: These are conditions caused by mutations in genes on the X chromosome. Since males have one X and one Y chromosome (XY), they will express the disorder if they inherit the affected X chromosome because they do not have a second X chromosome to mask the effect.
• Inheritance in Males: A male inherits his X chromosome from his mother and his Y chromosome from his father.

Step 4: Analysis, Verify and Summarize

• A male with an X-linked recessive disorder has the genotype X^rY, where X^r represents the X chromosome carrying the recessive allele for the disorder.
• Since males have only one X chromosome, the presence of the recessive allele on this chromosome will result in the expression of the disorder.

Final Answer

The allele combination for a male with an X-linked recessive disorder is $X^rY$.