1. Gene Interaction

2. Types of Gene Interaction
Definition: coordinated action of non-allelic genes controlling a single phenotypic trait
Type 1: simple unmodified Mendelian ratios
Type 2: epistasis: modified Mendelian rations
Type 3 Quantitative “polygenic” continuous variation (height)

3. Epistasis
Definition: non-reciprocal interaction of non-allelic genes so that one gene masks the phenotypic expression of another non-allelic gene (opposite: pleiotropy)
Example Labrador Retrievers (E and B gene) EE/Ee BB/Bb
Dilute golden -> brown -> black pigment
E_B_ = black
E_bb = brown
eeB_ = golden
eebb = golden Altered ratio: 9:3:4
Genotype ee is epistatic (standing above or masking remaining steps) to B_
Geneotype B_ is hypostatic to ee

4. Plumage in Parakeets (genes A and B)
Gene A
Gene B
Blue + yellow
White -> Blue (with gene A)
White -> Yellow (gene B)

5. Parakeets If A is present and no B -> blue
If B is present and no A -> yellow
If B and A is present -> green
Neither (aa and bb) -> white pigment
Precursor is white for both A and B

6. In horses

7. Mice

8. Kernel Anatomy

9. Pathways Colorless 1 -> (gene A1catalyzes)-> colorless 2
Gene A 2 catalyzes to bronze pigment
Gene Bz1 catalyzes to red pigment
Gene Bz2 catalyzes to purple pigment
Gene C and R must be present to active pathway
Gene CI inhibits action of A1 = 13:1 ratio
Gene rr inhibits A1 =9:7 ratio
Gene bz1 bz1 inhibits Bz2 = 9:3:4
Gene a2a2 inhibits phenotypic expression of gene Y (yellow endosperm) 12:3:1