ABSTRACT
Genes play an important role in the formation of the human body. One has a stomach, muscles, and bones, their cells are animal cells and not plant cells, and they have 46 chromosomes. Cells differentiate even though each cell in the body has exactly the same genes on the same chromosomes. Hox genes are the same in most animals. Bugs, lions, and humans all have the same genes to tell their cells which end of the body the head should go on. In some cases, animals are two-in-one. For example, all earthworms have both male and female sex organs in their same body, so they can produce both sperm and eggs. Some animals, however, such as fruit flies those teeny black flies that sometimes buzz around your fruit bowl have both an X and a Y chromosome, but the genes on the Y chromosome do not determine if a fly will be male.
