Gene Interaction

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)

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

http://www.steve.gb.com/images/science/recessive_epistasis.png

Plumage in Parakeets (genes A and B)

Gene A Gene B

Blue + yellow White -> Blue (with gene A)

White -> Yellow (gene B)

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

In horses

http://courses.bio.psu.edu/fall2005/biol110/tutorials/tutorial5_files/figure_14_11.gif

Mice

http://www.zo.utexas.edu/faculty/sjasper/images/14.11.gif

Kernel Anatomy

http://www.fao.org/DOCREP/W0073e/p255.gif

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