Genetics and Heredity Predicting Genotypes and Phenotypes using the Punnett Square Objective • Recognize genotypes and phenotypes and predict genetic outcomes of an animal through use of the Punnett Square. Gene • The basic physical unit of heredity Chromosomes • Long strands of DNA and associated proteins present in the nucleus of every cell Locus • The specific location of a gene on a chromosome. Allele • Any of the possible forms in which a gene for a specific trait can occur. • Ex: A, a Genotype • The genetic constitution of an organism. • Determines the phenotype. Phenotype • Physical characteristics of an animal. • Examples: -Horned/Polled -Black/Red Homozygous • A one-locus genotype containing functionally identical genes. • Example: -BB, bb, GG, gg Heterozygous • A one-locus genotype containing functionally different genes. • Example: -Rr, Gg, Bb Dominant • A gene that is expressed phenotypically. • Example: -Black / Red -Brown / Blue Recessive • A gene that is phenotypically expressed in the homozygous state but has its expression masked in the presence of a dominant gene. • The “weaker” gene Punnett Square B B B BB BB b Bb Bb B=Black b=Red