ratios

Monohybrid cross

A cross involving one pair of contrasting traits

What is the F2 phenotypic ratio of a monohybrid cross?

3:1

Dihybrid cross

A cross involving two pairs of contrasting traits

What is the F2 phenotypic ratio of a dihybrid cross?

9:3:3:1

Trihybrid cross

A cross involving three pairs of contrasting traits

What is the F2 phenotypic ratio of a trihybrid cross?

27:9:9:9:3:3:3:1

Dihybrid testcross

A two-trait heterozygote crossed with an individual homozygous recessive for both traits

What is the expected ratio of a dihybrid testcross when the tested individual is heterozygous for both genes?

1:1:1:1

Trihybrid testcross

A three-trait heterozygote crossed with an individual homozygous recessive for all three traits

What is the expected ratio of a trihybrid testcross when the tested individual is heterozygous for all three genes?

1:1:1:1:1:1:1:1

Incomplete dominance and co dominance

Neither allele is completely dominant, so the heterozygote has an intermediate phenotype ( red and white make pink)

two different versions (alleles) of the same gene are both fully and equally expressed in a heterozygous individual(red and white make red and white)

What is the F2 phenotypic ratio for incomplete/ codominance dominance?

1:2:1

Recessive epistasis

The homozygous recessive genotype at one locus masks the expression of alleles at another locus

What is the F2 phenotypic ratio for recessive epistasis?

9:3:4

Dominant epistasis

A dominant allele at one locus masks the expression of alleles at another locus

What is the F2 phenotypic ratio for dominant epistasis?

12:3:1

Complementary gene interaction

Two gene pairs complement one another; at least one dominant allele at each locus is required for expression of one phenotype

What is the F2 phenotypic ratio for complementary gene interaction?

9:7

Novel phenotype interaction

Gene combinations result in a new or novel phenotype in the F2 generation

What is the F2 phenotypic ratio for a novel phenotype interaction?

9:6:1