Which pedigree symbol is used to represent a female carrier of a recessive X-linked trait? An empty circle. A half-filled circle. An empty square. A filled square.

A half filled circle

Explanation:

In pedigrees, females are always denoted with a circle, and males with a square. Affected individuals usually have coloured or filled symbols, whereas unaffected individuals have an empty symbol.

In the case of carriers, this is often denoted as a half filled symbol. I. e. the shape is filled on one side and not the other, split down the middle). Sometimes a carrier of an X linked condition is denoted as a half filled, but instead of left vs right, the circle is filled with a smaller circle in the middle.