Final answer:
An all-white circle in a pedigree represents a normal female, who may be genotypically normal or a carrier in the case of X-linked recessive diseases.
Step-by-step explanation:
In a pedigree, symbols are utilized to represent individuals and their genetic traits. Specifically, circles symbolize females, and the colors inside these circles or squares indicate whether individuals have a particular trait. For example, in the context of recessive traits, an individual with two recessive alleles, such as for an autosomal recessive disease, is usually represented by a filled symbol. An all-white circle, therefore, represents an individual without the recessive trait, who can either be genotypically normal or a carrier, depending on the context of the pedigree.
In the case of X-linked recessive diseases, the situation is slightly different. Females can be genotypically normal, carriers who are phenotypically normal, or affected with the disease; whereas males, due to possessing only one X chromosome, will either have the disease or be genotypically normal and cannot be carriers. Therefore, an all-white circle would indicate a normal female who does not express the disease phenotype. She may or may not be a carrier if the disease is X-linked recessive.