hybridized

3. Simple interaction (9:3:3:1 ratio)Bateson and Punnett gave classical example in fowl to show two genes influencing the same character. There are four types of combs recognised among fowls—pea, rose, walnut and single. These are caused by two allelomorphic pairs of genes symbolised by PPrr (pea), ppRR (rose). A cross between the two produces a new comb form in Fj generation called walnut (RrPp). The F[ generation on selfing produced F2 generation as follows—9 walnut, 3 pea, 3 rose and 1 single. Thus when dominant gene P is present alone (without other dominant gene R) the comb is pea type. When R is present alone, the comb is green or red or rose. But when both P and R are present there is an interaction and the comb becomes walnut. When no dominant gene is present, the comb is of double recessive, i.e., single type (Fig. 65.4).A Summary Chart of Common Types of Interaction of Genes Observeds.No.FactorsExamplesF2Phenotypic ratioP,Parent-1P2Parent-2FiIndividualF2 Population (Genotype and Phenotype)1.Simple interactionComb colour in fowl9:3:3:1RRpp Rose combrrPP Pea combR-P-Walnut combR-P-Walnut (9)R-pp Rose (3)rrP-Pea(3)rrpp Single (1)2.Epistasis(dominantepistasis)Body colour in dogsaaBB BlackAAbb WhiteA-B-White| A-B-| (9) WhiteA-MT~j (3) White 1aaB-(3) Blackaabb (1) BrownSeed coat colour in Cajanus cajan12:3:1BBrr Black seededbbRR Red seededB-R-Black seededir B-R-1 (9) Black L_____B-rr 1 (3) Black 1bbR-(3) Redbbrr (1) White3.Supplementary factors (Recessive epistasis)Flower colour in Antirrhinum9:3:4AAbb IvoryaaBB WhiteA-B-MagentaA-B- (9) MagentaA-bb (3) Ivory, aaB-1 (3) Whiteaabb (1) White jSkin colour in riceAAbb Black skinaaBB Albino skinA-B-Agauti colourA-B-(9) AgautiA-bb (3) BlackaaB1-" I (3) Albinoaabb j (1) Albino JAComplementary factors. IV V W V r 111colour of paddyAAbb GrayaaBB GrayA-B-RedA D ri u(9) Redi "/^bb1 (3) Gray1aaB-(3) Grayaabb ! (1) Gray JFlower colour in Lathyrus odoratus9 : 7CCpp White flowersccPP White flowersC-P-Red flowersC-P-(9) Redr c-pp1 (3) WhiteccP-(3) Whiteccpp J (1) White j5.Inhibitory factorsPigmentation in leaves of paddy13 : 3Ilpp Green pig.iiPP Purple pig.I-P-Green pig.I-P-(9) GreenI-pp (3) GreeniiP-(3) Purpleiipp (1) Green6.Duplicate factorsFruit shape of Capsella15 : 1AABB Triangularaabb Top shapedA-B-Triangular shapeA-B- (9) TriangularA-bb (3) TriangularaaB- (3) Triangularaabb (1) Top shapedAwned character in paddy grainsA1A1a2a2 Awneda j A2A2 AwnedA, - A2 AwnedA, - A2 (9) AwnedA j a2a2 (3) Awneda,a| A2-(3) Awneda^ aja2a2 (1) Awnless7.Polymorphism additive effectPericarp colour in wheat9:6:1Light redLight redR, - R2-Deep redR, - R2 (9) Deep redR, - r2r2 (3) Light redr,r,R2- (3) Light redrlrlr2r2 (1) WhiteC j C j . Deep redC|C|C2C2ColourlessC,-C2-Deep redC,-C2 Deep redC j c2c2 Light redLight redc1c,c2c2 White4. Complementary factors (9 : 7 ratio)Sometimes a trait is produced by the interaction of two or more genes situated on separate chromosomes which complement one another. In some varieties of sweet pea the following interaction of two pairs of genes has been noted, (Fig. 65.5) ccR-, C-rr and ccrr- white colour C-R-Red colour. It was observed by Bateson and Punnett in Lathyrus odoratus.Here gene C and R are complementory to each other and necessary for the production of colour in flower. When they are together (C - R -), red colour in petals develop.