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Epistasis
Epistasis occurs when one gene suppresses or masks the expression of another gene. There are different types of epistasis including dominant, recessive, duplicate dominant, and duplicate recessive epistasis. Epistasis ratios in offspring depend on the type of epistasis and can be 12:3:1, 9:3:4, 15:1, or 9:7. Modifier genes modify the effects or expression of another gene without masking it, like genes influencing coat color in mice. Pseudoalleles are two closely linked genes affecting the same trait that can undergo recombination like different eye color mutants in Drosophila.
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Epistasis
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- 3. EPISTASIS Definition: Suppression ofthe effect of a gene by another gene. mask A B Epistatic/Dominating Gene (the gene masking the effect of another gene) Regulated/Hypostatic Gene (gene whose functionality of the expression is masked or prevented) knip
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- 8. Mendelian Dihybrid PhenotypicRatio After the cross in F2 9 : 3 : 3 : 1 9 A_B_ 3 A_bb 3 aaB_ 1 aabb knip
- 9. Dominant Epistasis Example: Color ofsummer squash = 2 seperate genes A/a - White - Epistatic gene B - Yellow - hypostatic gene b - Green A B AA Aa aa knip
- 10. Dominant Epistasis AaBb xAaBb AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb white white white whitewhite white whitewhite whitewhite white white greenyellow yellowyellow Ratio: 12:3:1 12-white 3-yellow 1-green knip
- 11. Recessive Epistasis Example: Colorof mice = 2 seperate genes C - pigment c - no pigment - Epistatic Gene B - more pigment (black) b - less pigment (brown) cc - albino c B CC Cc cc knip
- 12. Recessive Epistasis Genotype CoatColor 9 B_C_ Black 3 B_cc Albino 3 bbC_ Brown 1 bbcc albino Ratio: 9:3:4 knip
- 13. Duplicate Dominant Example:Kernel Colorin Wheat Product Enzyme B Gene B Precursor Enzyme A Gene A Genotype Kernel Phenotype Enzymatic Activities 9 A_B_ colored kernels functional enzyme from both genes 3 A_bb colored kernels functional enzyme from the A gene pair 3 aaB_ colored kernels functional enzyme from the B gene pair 1 aabb colorless kernels non-functional enzymes produced at both genesRatio: 15:1 BA OR knip
- 14. Duplicate Recessive:Complementary Genes Example:Flowercolor in sweet pea Intemediate Enzyme B Gene P Precursor Enzyme C Gene C Genotype Kernel Phenotype Enzymatic Activities 9 C_P_ Flowers colored, anthocyonin produced functional enzyme from both genes 3 C_pp Flowers white, no anthocyonin produced p enzyme non- functional 3 ccP_ Flowers white, no anthocyonin produced c enzyme non- functional 1 ccpp Flowers white, no anthocyonin produced c and p enzyme non-functional Ratio: 9:7 Anthocyonin C PAND knip
- 15. Dominant Recessive Genotype Phenotypeand genetic explanation 9 K_D_ no malvidin because dominant D allele is present 3 K_dd maldivin productions because dominant D allele is absent 3 kkD_ no malvidin because recessive k and dominant D alleles are present 1 kkdd no malvidin because recessive k allele is present D K malvidin production regulate the K gene Ratio: 13:3 knip Example: Production of Malvidin in the plant of Primula
- 16. TYPE OF EPISTASISRATIO Dominant 12:3:1 Recessive 9:3:4 Duplicate Dominant 15:1 Duplicate Recessive 9:7 Dominant Recessive 13:3 knip
- 17. Modifier Genes A genethat can modify the effects or expression of another gene. Example : coat color of the mice Gene - controls the color B - black b - brown Gene - influence the color D - fullcolor d - dilute or faded color Genotype Coat Color 9 B_D_ black 3 B_dd dilute black 3 bbD_ brown 1 bbdd dilute brown The D gene does not mask the effect of B gene, rather it modifies its expression. knip
- 18. Pseudoalleles State in whichtwo genes with similar functions are located so close to one another on a chromosome that they are genetically linked. Characeristics of Pseudoalleles 1. These are closely linked allele within which crossing over occur. 2. They affect the same character. knip
- 19. Example of Pseudoallele Redeye color Drosophila has different mutants like white and apricot. They affect pigmentation i.e., affect the same character. So they are allelic. They can undergo recombination. knip
Editor's Notes
- #4 Epistasis- type of gene interaction where one gene mask the effect of another gene.
- #5 Thses gene are located at different chromosomes or even the same chromosomes but different loci. The one that dominates is the epistatic gene and the one that gets dominated is the hypostatic gene.
- #6 If the epistatic gene is dominating in its dominant form- Dominant Epistasis ,recessive form-Recessive epistasis
- #7 If one A is capital or dominant it will not let the B express itself.
- #8 It will not let the B express itself even in its recessive form.
- #10 Before we plot the cross let us take this situation. As long as capital W is there this which is responsible for production of white flower this Y is not able to express itself.
- #12 Before we plot the cross let us take this situation. As long as capital W is there this which is responsible for production of white flower this Y is not able to express itself.
- #14 2 genes re acting as epistatic gene.
- #15 Because both genes are required for the correct phhenotype, this epistatic interaction is called complementary gene action.