The basic number of chromosomes in the body cells of a species is called the "somatic number" and is labelled "2n". In humans 2n = 46: we have 46 chromosomes. In the sex cells the chromosome number is "n" (humans: n = 23). So, in normal diploid organisms, chromosomes are present in two copies, one from each parent (23x2=46). The only exception are the sex chromosomes. In mammals, the female has two X chromosomes, and the male one X and one Y chromosome.