The genes you have are called your genotype

The genes that are expressed (shown) are your phenotype

When we write a genotype we use a capital letter for the dominant trait and a lowercase letter for the recessive trait. The letter chosen is usually the first letter of the dominant trait

-For example when talking about purple and white pea plants

-Purple is the dominant trait and white is recessive

-So the possible genotypes for flower color are:

PP= Homozygous dominant purple

pp= Homozygous recessive white

Pp= Heterozygous purple

A plant that is PP can only make P gametes

A plant that is pp can only make p gametes

-If you cross-fertilize the two the only possible offspring are Pp

If the heterozygous offspring (Pp) reproduce, their offspring can be any of the four possible combinations

PP, Pp, pP, pp

Punnett Squares

We can figure our the possible allele combinations of offspring by using a Punnett Square

Mendel then started testing other traits in the pea plants

Lets do some practice Punnett Squares using these traits!

What if we want to do a Punnett Square for more than one trait?

-We can do what is called a dihybrid cross. A cross between two traits