1. Alleles Allele - one alternative form of a given gene pair.
Tall and dwarf are the alleles for the height of a pea plant.
More than two alleles can exist for any specific gene, but only two of them will be found within any individual.
We use letters to denote alleles, since every gene has two alleles, all genes can be represented by a pair of letters.
TT = tall, Tt = tall, tt = dwarf

2. Other types of crosses
1. Incomplete Dominance- There is no dominant or recessive, the heterozygous condition results in a "blending" of the two traits. Example: Snapdragons can be red, white, or pink (heterozygous)

3. 2. Codominance
Occurs when both alleles for a gene are expressed in a heterozygous offspring. Neither is dominant or recessive.
Ex- White + Red horse= Roan (white and red hairs mixed together). +