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.
