sex chromosome

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Either of a pair of chromosomes in diploid cells, or a single chromosome in haploid cells, carrying genes that determine the sex and sex-linked characteristics of an organism. Most mammals, including humans, have one pair of sex chromosomes in diploid cells, designated XX in females and XY in males.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun genetics either of a pair of chromosomes (in most animals and plants) whose combination determines the sexual characteristics of an individual.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun (genetics) a chromosome that determines the sex of an individual