Chromosomes are inherited from the parents. One chromosome from each of 23 pairs came from each of the parents. The two chromosomes of a pair (except for the sex chromosomes) contain the same genes, but the genes have small differences. The X and Y Chromosomes determine the organism’s sex. One chromosome pair - the sex chromosomes - is unique. Typically females have two X chromosomes and males have an X and a Y. Mothers always pass an X chromosome on to their children. Whether the father passes on his X chromosome (leading to a pair of X chromosomes) or his Y chromosome (making a mixed set) determines your sex. Chromosomes get shuffled when eggs and sperm are made. Though most adult cells contain two sets of chromosomes, sperm and egg cells are different. These special cells have just one chromosome from each pair. Which chromosome they get from each pair is random, making each sperm or egg cell unique. There is also a bit of mixing before the chromosomes are sorted into individual sperm or egg cells. Chromosomes from each pair in a mother or father, respectively, make contact and exchange pieces of DNA, creating hybrid chromosomes.