A typical human karyotype has 23 types of chromosomes
arranged from largest to smallest. In males and females 22 of these chromosomes
look exactly the same and they are called autosomes. The 23rd pair of
chromosomes is the sex chromosome which differentiates males from females.
Females have 2 copies of the x chromosome. Males have a copy of both x and y
chromosome to make the 23rd pair.
Chromosomes can also have abnormalities that
result to different conditions and identifiable traits. A most common
chromosomal abnormality is the condition called Down Syndrome, where chromosome
21 has a third copy because of an abnormal cell division.
