Different variations of a gene: Allele An individual's collection of genes and alleles: Genotype An allele that is only expressed in a homozygous state: Recessive allele An allele that is expressed in a heterozygous state: Dominant allele A unit of heredity that usually encodes a protein: Gene A diagram used to predict genotypes: Punnett square When dominant alleles mask recessive allele effect: Complete dominance When recessive alleles have a partial phenotypic effect: Incomplete dominance A specific characteristic or attribute of an organism: Phenotype The offspring generation: F1 generation