Before sexual reproduction can take place, each parent produces sex cells. Sex cells have half of the genetic information that body cells have. thus, when the genetic information from two parents combines, the offspring have a full set of genetic information. The offspring will have the same total number of chromosomes as each of its parents.
In body cells, most chromosomes are found in pairs that have the same structure and size. These homologous chromosomes (huh-MAHL-uh-guhs KRO-muh-sohmz) carry the same genes. A homologous chromosome pair may have different versions of the genes they carry. One chromosome pair is made up of sex chromosomes. Sex chromosomes control the development of sexual characteristics. In humans, these chromosomes are called X and Y chromosomes. Cells with a pair of every chromosome are called diploid (DIP-loyd). Many organisms, including humans, have diploid body cells.
PHOTO INFORMATION: This photo shows the 23 chromosome pairs in a human male. Body cell contain all of these chromosomes. Sex cells contain one chromosome from each pair. If you notice at the bottom right of this photo, there is an "X" and a "Y" chromosome. Males of an X and a Y chromosome.
You'll notice that this picture also has 23 chromosome pairs just like the top photo. However, you should notice at the bottom of this photo, there are two "X" chromosomes and that "Y" chromosome is missing. This means that this photo is of a female.