Vocabulary for Punnett Squares In describing the inheritance of genes, some additional terms are useful. Phenotype An organism’s Phenotype is the physical appearance of a trait. For example, in the “Class Traits” activity, there were two possible phenotypes for hair line-widows peak or no widows peak. For Mendel’s peas, the phenotypes for seed shape were round or wrinkled. What are the two possible phenotypes for earlobe style? Allele form of a trait P or p inside Easter egg halves Genotype Genotype is the organism’s allele combinations, or gene type. There are three possible genotypes for chin shape— CC, Cc, or cc. Three additional terms can be used to describe a genotype: homozygous dominant = both genes are dominant (ex: WW); called Purebreds by Mendel. homozygous recessive = both genes are recessive (ex: ww); called Purebreds by Mendel. heterozygous = one dominant and one recessive gene (ex: Ww); called Hybrids by Mendel. “Hard” Science Words By now, you’ve probably begun to recognize that many “hard” science words are made up of prefixes, roots, and suffixes, and if the word is broken down, the meaning is easier to remember. For Example In the words heterozygous and homozygous the prefix “hetero” means different; and the prefix “homo” means same. So, heterozygous means there are two different alleles; homozygous means there are two of the same alleles (either two dominant or two recessive).