Recessive and dominant genes
So there are two types of genes, one is a dominant gene and the other is called recessive. A dominant gene the more powerful type of gene, so say that you had black construction paper and a Kleenex. If you put the Kleenex over the construction paper you can still through the Kleenex, but say that you put the paper over the Kleenex the paper would totally cover the Kleenex. That's how recessive and dominant genes work, the construction paper being dominant and the Kleenex being recessive.