Final answer:
A gene located on the X chromosome but not on the Y chromosome is called a sex-linked gene, specifically an X-linked gene.
Step-by-step explanation:
In humans, a gene that is found on the X chromosome but not on the Y chromosome is referred to as a sex-linked gene. Specifically, these genes are known as X-linked genes. The X chromosome contains a greater number of genes compared to the Y chromosome, which is much shorter and has fewer genes. Females possess two X chromosomes (XX), whereas males have one X and one Y chromosome (XY), making females homozygous for X-linked genes and males hemizygous. These patterns of inheritance are crucial because they explain why certain traits and disorders are more commonly found in one sex than the other.
A sex-linked gene in humans is one located on the X chromosome but absent on the Y chromosome, specifically termed X-linked genes. As females have two X chromosomes (XX) and males have one X and one Y chromosome (XY), females are homozygous for X-linked genes, while males are hemizygous. The X chromosome carries a greater number of genes than the Y chromosome, contributing to the phenomenon of X-linked inheritance.
The hemizygosity of males for X-linked genes means that any recessive mutation on the X chromosome is expressed phenotypically in males. In contrast, females would need to inherit two copies of the recessive allele to manifest the trait. This pattern of inheritance explains why certain traits and disorders linked to X-linked genes, such as color blindness and hemophilia, are more frequently observed in males than females. Understanding these sex-linked patterns is essential in genetics and provides insights into the inheritance of specific traits and disorders in human populations.