Solving Punnett Squares

Vocabulary Review Dominant Recessive The trait always appears in offspring. The dominant allele is a capital letter (A,B) Recessive The trait only appears it is alone (aa, bb) The recessive allele is a lower-case letter (a,b)

Vocabulary Review Homozygous – two identical copies of an allele Homozygous dominant: two dominant alleles (BB) Homozygous recessive: two recessive alleles (bb)

Vocabulary Review Heterozygous: Two different copies of an allele (Bb)

Overview of Steps Step 1: Fill in trait chart. Step 2: Identify parental genotype from chart. Step 3: Complete Punnett Square

Trait Chart This is a quick reference sheet you make to keep track of genotypes and phenotypes. Genotype Phenotype

Trait Chart con’t Genotype Phenotype Homozygous Dominant (BB) Heterozygous (Bb) Homozygous Recessive (bb) In complete dominance, the genotype column is always the same

Trait Chart con’t In complete dominance, the dominant trait appears in the homozygous dominant and the heterozygous genotypes Genotype Phenotype Homozygous Dominant (BB) Dominant Trait Heterozygous (Bb) Homozygous Recessive (bb) Recessive Trait

Practice Problem One: Cut leaves are recessive to whole leaves. A homozygous recessive plant is crossed with a heterozygous plant. What is the phenotypic ratio of the offspring?

Practice Problem Two Black fur is recessive in beavers. A heterozygous beaver breeds with homozygous brown beaver. What is the phenotypic ratio of their offspring?