1. Solving Punnett Squares

2. 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)

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

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

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

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

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

8. 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

9. 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?

10. 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?