Question

which symbol is used to label a male that expresses a sex - linked disorder on a pedigree?

Explanation:

In pedigree analysis, squares represent males. A filled - in (colored) square indicates that the male expresses the trait (in this case, a sex - linked disorder). A circle represents a female. A half - colored circle or square is not a standard symbol for expressing a sex - linked disorder in the context of basic pedigree notation. A white square represents a male who does not express the disorder.

Answer:

The last option (the filled - in square) is used to label a male that expresses a sex - linked disorder on a pedigree.