Terminology

Gametes

Parental haploid reproductive cells.

Overview

Number of Unique Gametes for Independent Assortment

$$2^n$$ where n is the number of heterozygous loci

Dihybrid Crosses

• Starting with P generation
  • Assign alleles
  • Write out mates genotypes
  • Write out all possible gametes.
  • Combine gametes into offspring
• Starting with F1 generation
  • Write out all mates genotypes
  • Write out all possible gametes
  • Setup dihybrid punnet squares
  • Combine gametes into offspring
  • Note genotypic/phenotypic ratios.

Dihybrid crosses only work if genes are on two different chromosomes and can independently assort.

If genes can independently assort, you can break your dihybrid cross into two monohybrid crosses for each gene and multiply their probabilities together.

Combining Monohybrid Crosses into Dihybrid Probabilities

For each independently assorting gene:

$$3/4 \text{ dom} * 3/4 \text{ dom}$$

$$9/16$$ total dominant

$$3/4 \text{ dom} * 1/4 \text{ rec}$$

$$3/16$$ total heterozygous

$$1/4 \text{ rec} * 3/4 \text{ dom}$$

$$3/16$$ total heterozygous

$$1/4 \text{ rec} * 1/4 \text{ rec}$$

$$1/16$$ total rec

Probability Rule

• The probability of two independent events both happening is the probability of each independent event multiplied (AND).

$$P(\text{smooth AND yellow}) = P(smooth) * P(yellow)$$