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X chromosome

(Science: genetics) A sex chromosome. In mammals paired in females (XX), in amphibia paired in males. The sex chromosome that is present in both sexes: singly in males and doubly in females; human females normally have two X chromosomes.One of the sex chromosomes found in both sexes. The X chromosome in males can express many dominant sex-linked traits because the shorter opposing Y-chromosome has no homologous genes to challenge the dominance of some genes on the Y chromosome.