Final answer:
A woman is called a carrier if she has one X-linked recessive allele only and does not exhibit any phenotype effects. Carriers are individuals who have a recessive allele for a particular trait but do not show any symptoms. They can pass the recessive allele to their offspring.
Step-by-step explanation:
Females who have one X-linked recessive allele only and do not exhibit any phenotypic effects are called carriers. Carriers are individuals who have a recessive allele for a particular trait but do not show any symptoms because they have another normal allele. They can pass the recessive allele to their offspring, who may or may not exhibit the trait.
For example, in humans, some X-linked recessive traits include red-green color blindness, hemophilia, and muscular dystrophy. Carrier females who are heterozygous for these diseases pass the disease to half of their sons, but they may not show any symptoms themselves.
Due to the presence of two X chromosomes, females have the chance to inherit two copies of a recessive allele, which is why recessive X-linked traits appear more frequently in males than females.