Dr. Jayakara Bhandary M.Associate Professor of BotanyGovernment College, Karwar – firstname.lastname@example.org GENE INTERACTIONS (FOR BOTANY STUDENTS OF B. SC. SEMESTER VI, PAPER 1, KARNATAKA UNIVERSITY, DHARWAD
INTRODUCTION Non-Mendelian patterns of Inheritance – Deviations from Mendelian Ratios (3:1, 9:3:3:1). 2 types – Allelic and Non-allelic . Non- Allelic Gene Interactions: No complete dominance-recessive relationship between alleles of a gene pair Together in Heterozygous condition (Aa), interact and produce new phenotypes – Examples: Incomplete Dominance, Co-Dominance Co-
NON-ALLELIC GENE INTERACTION One Character – influenced by 2 or more pairs of non-allelic gene pairs (Aa, Bb, Cc...). Phenotypes decided by interaction between the alleles of these non-allelic genes. Mendelian ratios modified. Examples: Supplementary interaction, Epistasis, Complementary Interaction, Epistasis, Duplicate genes, etc.
CO-DOMINANCE Alleles for human blood groups (ABO) IA, IB IO – 3 alleles IA IB – in heterozygous condition produce Antigen A and Antigen B- AB blood. Both are effective completely - Codominant alleles (IO is recessive to both IA IB).
INHERITANCE OF COMB TYPES IN CHICKENS Example for non-allelic gene interaction without deviation of Mendelian dihybrid ratio (9:3:3:1). Different chicken breeds – different type of combs Rose Pea Single Walnut
GENETICS OF COMB TYPES… Gene R - Rose comb, Gene P – Pea comb R_pp – Rose, rrP_ - Pea comb, rrpp – Single, Hybrid of Rose and Pea produces Walnut – R_P_.Cross between Rose and Pea results in F2 population of 9 walnut, 3 Rose, 3 Pea and 1 single (same as Mendel’s dihybrid ratio). Supplementary genes?
SUPPLEMENTARY INTERACTION One gene independent in action Second gene dependent on or supplementary in action to first gene. Effective only with first gene. Ex: Coat colour in mice A – Black clour, independent gene B – Supplementary, Converts black into Agouti
A_B_= Agouti, A_bb = Black, aaB_ = White, aabb = White P- Agouti (BBAA) X White (bbaa) F1 --- Agouti (BbAa) F2 Phenotypic Ratio - 9 Agouti, 4 white and 3 black
COMPLEMENTARY INTERACTION 2 non-allelic genes together produce an effect by complementing each others action. Each gene, when present alone, no effect Ex: Flower colour in Sweet Peas Genes C P together – Red/Purple flower Only C or P /no CP = White flower
(CCpp CCpp) (ccPP ccPP)White (CCpp) X White (ccPP) F2: Purple 9 , White 7
EPISTASIS One non-allelic gene masking/suppressing the action of another gene. Literally means ‘ sitting upon One gene sits upon’. upon another gene, prevents its expression. Suppressor gene= Epistatic gene gene, affected/inactivated gene = Hypostatic gene gene. Different types- Dominant/Recessive epistasis, Unidirectional/Bidirectional Epistasis.
EXAMPLE FOR EPISTASIS Feather colour in chickens: Gene C codes for colored feathers. Another non-allelic gene A is epistatic to C. In the presence of A, C cannot produce coloured feathers. Therefore, feathers are white. Only when A is absent (aa), C is effective. C_A_ = White (A epistatic to C), ccA_ = White (no C gene), ccaa= White C_aa = Coloured. A cross between White (CCAA) and white (ccaa) produces all White feathers in F1 (CcAa). In F2, White and coloured are obtained in 13:3 ratio. Some also treat Supplementary interaction as Epistasis (Coat colour in animals, 9:4:3 ratio).