Autosomes and sex chromosomes

Of the 46 chromosomes in a human body cell, 44 do one kind of job and the remaining two do something different as well.

Autosomes

The chromosomes that carry the genes for body characteristics and have no part in determining sex.

44 chromosomes — 22 homologous pairs

Sex chromosomes

The one pair that determines the sex of the individual. They carry ordinary genes as well.

2 chromosomes — 1 pair

Written as a total

A human body cell is therefore 44 autosomes plus 2 sex chromosomes, which is 46 altogether, or 23 pairs. A gamete gets one of each pair: 22 autosomes plus 1 sex chromosome, making 23.

Figure to be added

Figure 20.21 — the 46 chromosomes of a human female arranged in 23 numbered pairs, with the last pair matching in size.

Figure to be added

Figure 20.22 — the 46 chromosomes of a human male arranged the same way, with the last pair visibly unequal: one large chromosome beside one much smaller one.

Only the last pair differs between the two pictures

Set the two arrangements side by side and pairs 1 to 22 are the same in both. The whole difference between the two sexes, in this picture, sits in the twenty-third pair.

44 plus 2

A human body cell carries 44 autosomes and 2 sex chromosomes. The autosomes carry body characteristics; the last pair decides sex.