Over 2 dominance
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Over dominance is a form of non-additive gene interaction where heterozygous individuals exhibit superior traits compared to either homozygous genotype. It is exemplified in rabbits where the A1A2 genotype produces antigen 3 in addition to antigens 1 and 2. Epistasis is another form of non-additive gene interaction that involves two or more pairs of non-allelic genes interacting. In horses, coat color is determined by epistasis between genes for black (B) vs chestnut (b) color and a dominant white (W) gene, which inhibits the expression of B and b.
Over 2 dominance
- 1. Over Dominance Definition: Over Dominance is the interaction between genes that are alleles and result in the heterozygous individuals being superior to either of their homozygotes. When A1 and A2 Gene occurs together: Genotypes are: A1A1, A1A2 and A2A2 Example: A particular blood type in rabbits
- 2. Over Dominance • Genotype A1A1 produces Antigen 1 • Genotype A2A2 produces Antigen 2 • Genotype A1A2 Not only produces Antigen 1 and 2 But also produce Antigen 3 Example in Human haptoglobinus, a protein produced by genes with a specific property of binding hemoglobines.H1H1,H1H2,H2H2 Over dominance affects traits of fitness/ vigor
- 3. EPISTASIS • Epistasis is another form of non additive gene action. • Epistasis involves two or more pairs of genes which are not alleles. • In over dominance the action between genes of a particular pair (A1 & A2) as heterozygotes give different phenotypic expression than when these genes are homozygous pairs.
- 4. EPISTASIS • In Epistasis the action is between entirely different pair of genes and not between members of the same gene pair. • In epistasis the two or more different pairs of genes may be on the same chromosome or on different chromosomes. In Horses, several coat colors are determined by epistasis.
- 5. EPISTASIS • Black and chestnut are two basic coat colors in horses and these colors are affected by two alleles. • The dominant gene B= Black. • The recessive gene b= Chestnut. • These two genes (B and b) segregates in the gamete, recombine in zygote and express there phenotypes accordingly. • Some horses posses white color , this is referred as dominant gene W (white gene)
- 6. • BBww Black color • Bbww Black color • bbww Chestnut color Dominant White gene will produce • BBWw White color • BbWw White color • bbWw White color • The dominant white gene W inhibits the expression of either the black B or chestnut gene b. • Thus W is the epistasis to these two genes.
- 7. • aaBBww black color • aaBbww black color • AaBBww bay color • AaBbww bay color • AABBww bay color • AABbww bay color
- 8. • AAbbCCww chestnut color • AabbCCww chestnut color • AAbbC ͨͬ Cww palomino • AabbC ͨͬ Cww palomino • AAbbC ͨͬC ͨͬCww type A, pseudo albino • AabbC ͨͬC ͨͬCww type A, pseudo albino