The first people to speculate that it might be due to chromosomal abnormalities were Waardenberg and Bleyer in the 1930s. The Chromosomes Chromosomes are thread-like structures composed of DNA and other proteins. They are present in every cell of the body and carry the genetic information needed for that cell to develop. Human cells normally have 46 chromosomes which can be arranged in 23 pairs. Each member of a pair of chromosomes carries the same information, in that the same genes are in the same spots on the chromosome.
Human cells divide in two ways.
In this method, one cell becomes two cells which have the exact same number and type of chromosomes as the parent cell. So, normal eggs and sperm cells only have 23 chromosomes instead of 46. This is what a normal set of chromosomes looks like. Note the 22 evenly paired chromosomes plus the sex chromosomes. The XX means that this person is a female.