Dr. Jayakara Bhandary M.Associate Professor of BotanyGovernment College, Karwar – 581301mbjaikar@gmail.com

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 NonAllelic and NonAllelic and NonAllelic and Non----allelic .allelic .allelic .allelic .Allelic Gene Interactions:Allelic Gene Interactions:Allelic Gene Interactions:Allelic Gene Interactions:Allelic Gene Interactions:Allelic Gene Interactions:Allelic Gene Interactions: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, CoIncomplete Dominance, CoIncomplete Dominance, CoIncomplete Dominance, Co----DominanceDominanceDominanceDominance

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.alleles of these non-allelic genes.

�Mendelian ratios modified.� Examples: Supplementary interaction, Supplementary interaction, Supplementary interaction, Supplementary interaction, Complementary Interaction, Complementary Interaction, Complementary Interaction, Complementary Interaction, EpistasisEpistasisEpistasisEpistasis, , , , Duplicate genes, Duplicate genes, Duplicate genes, Duplicate genes, etc.

INCOMPLETE DOMINANCE

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CO-DOMINANCE

� Alleles for human blood groups (ABO)

� IA, IB & IO –3 alleles � IA & IB – in heterozygous condition produce Antigen condition produce Antigen A and Antigen B- AB blood.

� Both are effective completely - Codominantalleles

� (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 combscombs

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_.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� Ex: Coat colour in mice

� A – Black clour, independent gene� B – Supplementary, Convertsblack into Agouti

A_B_= Agouti, A_bb = Black, aaB_ = White, aabb = White

P- Agouti (BBAA) X White (bbaa)F1 --- Agouti (BbAa)

F2 Phenotypic Ratio F2 Phenotypic Ratio F2 Phenotypic Ratio F2 Phenotypic Ratio ---- 9 Agouti, 4 white and 3 black9 Agouti, 4 white and 3 black9 Agouti, 4 white and 3 black9 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� Ex: Flower colour in Sweet Peas� Genes C & P together – Red/Purple flower� Only C or P /no CP = White flower�

White (White (White (White (CCppCCppCCppCCpp) X White () X White () X White () X White (ccPPccPPccPPccPP))))

F2: Purple 9 , White 7F2: Purple 9 , White 7F2: Purple 9 , White 7F2: Purple 9 , White 7

EPISTASIS

� One non-allelic gene masking/suppressing the action of another gene.

� Literally means ‘ sitting uponsitting uponsitting uponsitting upon’. One gene sits upon another gene, prevents its expression.upon another gene, prevents its expression.

� Suppressor gene= EpistaticEpistaticEpistaticEpistatic genegenegenegene, affected/inactivated gene = Hypostatic geneHypostatic geneHypostatic geneHypostatic gene.

� Different types- Dominant/RecessiveDominant/RecessiveDominant/RecessiveDominant/Recessive epistasis, Unidirectional/BidirectionalUnidirectional/BidirectionalUnidirectional/BidirectionalUnidirectional/Bidirectional Epistasis.

EXAMPLE FOR EPISTASIS� Feather Feather Feather Feather colourcolourcolourcolour in chickens:in chickens:in chickens:in chickens:� Gene CCCC codes for colored feathers. Another non-allelic gene AAAA is epistatic to C. In the presence of A, C cannot produce colouredfeathers. 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), � 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 13:313:313:313:3 ratio.

� Some also treat Supplementary interaction as Epistasis (Coat colour in animals, 9:4:3 ratio).