The genes for many traits are passed down in families from parents to children. For example, if your parents have black hair, then it is likely you and your brothers and sisters will have black hair. Once in awhile, though, this doesn't happen and parents with black hair will have a baby with blond hair.

How this happens is explained by the principle of "segregation." It is one of the basic principles of genetics and works for plants and animals alike.

Because you come from two parents, each parent will provide one half of your genes for any trait. That is called an "allele." So you have two alleles for each gene, one from each parent.

When both alleles tell your body the same thing, then your body "expresses" that gene. But what if you have two alleles that say different things? For instance, your earlobes, not something you usually think about, may be attached or free to flop. This is determined by one gene that comes in two forms: one for attached earlobes and one for free. If you got one allele for attached from your mom and one for free from your dad, how does your body know what kind of an earlobe to make? One of the earlobe alleles dominates over the other. No matter if the genes came from your mother or father, certain genes will dominate.

In the case of earlobes, "free to flop" is the dominant allele. So for you to have attached earlobes, the recessive trait, both your parents must have given you alleles for attached earlobes. Which means that they must have gotten them from their parents, who got them from their parents. Because attached earlobes is a recessive trait, it can sneak thru without being seen, from generation to generation, unlike a dominant allele. By watching how a trait is expressed in several generations and throughout an extended family, you can figure out some of the genes that each person must have.

The game will help you understand a tricky concept - how two parents who each have black hair (a dominant trait) can have a child with red hair (a recessive trait).