形成细胞内基因组或整个遗传物质的单体。染色体是通过缠绕蛋白质而被包装、压缩而成的遗传物质或DNA长链。染色体的数量和长度随物种而不同。人类有23对染色体（每对染色体中的两个单体分别来自父母双方）。一对称为性染色体因为它包含决定性别的基因。携带决定男性的基因的染色体称为Y染色体，携带决定女性的基因的染色体称为X染色体。其余的染色体称为常染色体。1号染色体最大，22号染色体最小。每条染色体有两臂称为p和q。
One of the physically separate segments that together form the genome, or total genetic material, of a cell. Chromosomes are long strands of genetic material or DNA that have been packaged and compressed by wrapping around proteins. The number and size of chromosomes varies from species to species. In humans, there are 23 pairs of chromosomes (a pair has one chromosome from each parent). One pair are called the sex chromosomes because they contain genes that determine sex. The chromosome carrying the male determining genes is designated Y and the corresponding female one the X chromosome. The remaining pairs are called autosomes. Chromosome 1 is the largest and chromosome 22 the smallest. Each chromosome has two “arms” designated p and q.