What are cells called that have two of the same form of an allele; what are cells called that have one of each of the two alleles for a character? What are three different genetic combinations, called genotypes, for each character? Why are there generally only two possible physical appearances, called phenotypes, of each trait?
Cells that have two of the same alleles for a certain character are called homozygous while cells that have one of each of the two alleles for the character are called heterozygous. The three different genotypes for each character include the homozygous dominant combination (two dominant alleles), the homozygous recessive combination (two recessive alleles), and heterozygous combination (one dominant allele and one recessive allele). There are generally only two possible phenotypes of each trait, dominant and recessive, because both the homozygous dominant and heterozygous genotypes will express the form of the character coded by the dominant allele.
