Chromosome

When a cell is getting ready to divide creating two daughter cells, it packs its DNA into bundles called chromosomes. Chromosomes are just bundles of DNA. For humans, there are consistently 23 pairs of chromosomes, each with a consistent size and shape. Chromosomes are numbered. Chromosome number 1 is the largest chromosome; chromosome number 2 a little smaller and so on. Among the 23 pairs of chromosomes there is a pair called the sex chromosomes. This is something of a misnomer, since there are many functions on the "sex" chromosomes that have nothing to do with sex. In females, the sex-chromosome pair consists of two similar size chromosomes called X chromosomes. Males have one X and one small Y chromosome.