Our bodies are made up of about 60 trillion cells. Each one of those cells manufactures proteins. The kinds of proteins any given cell makes determine its particular characteristics, which in turn create the characteristics of the entire body.
The instructions for making these proteins are stored in chemicals or molecules called DNA, which is organized into chromosomes. Chromosomes are found in the center, or nucleus, of all of our cells, including the eggs and sperm.
Chromosomes are passed down from generation to generation through the egg and sperm. Typically, we all have 46 chromosomes in our cells, two of which are sex chromosomes. In females, there are two Xs. In males there is an X and a Y.
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