Flexi Says: Humans have 23 pairs of chromosomes. Pairs 1-22 are autosomes. The 23rd pair are some combination of the sex chromosomes X and Y. Females have two X chromosomes, and males have an X and a Y chromosome. If a body has too few or too many autosomes, it usually won't survive to birth. The only case where a person can survive a missing chromosome is when an X or a Y chromosome is missing. This condition is called Turner syndrome and the genotype is noted as XO. Turner syndrome affects about 1 out of every 2,500 females, making it one of the most common chromosomal abnormalities.