- a sex chromosome of humans and most mammals that is present only in males and is paired with an X chromosome.
- the sex chromosome that occurs as one of a pair with the X-chromosome in the diploid cells of the males of many animals, including humansCompare X-chromosome
- The sex chromosome associated with male characteristics, occurring with one X-chromosome in the male sex chromosome pair.
- The sex chromosome that is paired with an X-chromosome in males. Most of the genes on the X-chromosome determine physical attributes associated with males, such as the development of testes. See more at sex chromosome. See Note at sex.