Definition:
Having two different alleles of a particular gene or genes.
(an Allele is a variant form of a gene.)
Simplification:
If the organism has one copy of two different alleles, it is heterozygous.
Eg: T and t
(T for tall and t for short)
Example:
Pea Plants
Pea plants can have red flowers and either be homozygous dominant (red-red), or heterozygous (red-white). If they have white flowers, then they are homozygous recessive (white-white). Carriers are always heterozygous.
