Final answer:
A half-shaded circle in a pedigree chart indicates a female carrier of a genetic disorder, particularly in the context of X-linked recessive inheritance, where females can carry a recessive allele without being affected by the disorder.
Step-by-step explanation:
In a pedigree chart, a half-shaded circle represents a female carrier of a genetic disorder. This indicates that the female has inherited a recessive gene for a disorder but does not show the disorder's phenotype. This is typical in X-linked recessive inheritance patterns.
For X-linked recessive disorders, males have a higher likelihood of exhibiting the disorder because they only have one X chromosome. A male with the recessive allele on the X chromosome will express the disorder. On the other hand, females have two X chromosomes, so they can be carriers if they have one recessive allele and one dominant allele. They are only affected if they inherit two recessive alleles.
A female carrier, as a half-shaded circle does not indicate the individual is affected with the disorder, but rather that she carries the gene and can pass it onto her offspring.