Before you start to learn the crosses you must know the basic terms of genetics.

The genotype is the genetic code. A homozygous genotype means you have either two dominant genes or two recessive genes and a heterozygous phenotype is a pair of one dominant gene and one recessive gene. Phenotype is the specific look that your genotype gives you. Now along with these terms you have codominance, incomplete dominance, and complete dominance. Incomplete dominance means that the offspring is a mixed phenotype of both the parents, codomince means that traits from both parents show (like having your mom's eyes and your dad's nose), and complete dominance means that the dominant trait is the one that shows when paired with a recessive. A really important thing to keep in mind when you are trying to determine phenotypes is the type of dominance.

The Types of Dominance

Incomplete dominance example in flowers:

This flower was the result of a cross between a pink flower and a white flower.
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Codominance example in flowers:

external image White+Rose.jpg crossed with a external image red-rose.jpggives you a external image Pink-Rose-Images.gif

And remember that when speaking about the phenotype you must always consider the type of dominance.