Final answer:
X-linked recessive traits are more frequently observed in males because they have only one X chromosome and express any recessive allele present. Females have two X chromosomes and must inherit two recessive alleles to express the trait, making them less likely to show symptoms but able to be carriers.
Step-by-step explanation:
X-linked Recessive Traits Frequency in Males and Females
When discussing X-linked recessive traits in humans or in Drosophila, it is important to understand that these traits are observed more frequently in males than in females. This phenomenon occurs because males have only one X chromosome, and thus a single recessive allele will be expressed. In contrast, females have two X chromosomes and must inherit two copies of the recessive allele, one from each parent, to express the trait. This difference in genetic makeup between males and females explains why X-linked recessive conditions like red-green color blindness, hemophilia, and muscular dystrophy are more common in males.
Females can be carriers of X-linked recessive traits without showing symptoms, as they have one normal allele to mask the effect of the recessive allele. A female carrier has a 50% chance of passing on the recessive allele to her offspring. Sons who inherit the allele will express the trait, while daughters may become carriers. It’s important to note that these general patterns can differ in organisms where the female has the non-homologous sex chromosomes, like birds, where the female is hemizygous for the X-linked genes.