1) The document discusses various types of non-Mendelian gene interactions including incomplete dominance, co-dominance, supplementary interaction, complementary interaction, and epistasis. 2) In incomplete dominance, alleles are not completely dominant or recessive and produce an intermediate phenotype in heterozygotes, like pink flowers from red and white parents. 3) Co-dominance occurs when both alleles are fully expressed in heterozygotes, such as AB blood from alleles for A and B antigens. 4) Epistasis involves one gene masking the expression of another gene.

1. Dr. Jayakara Bhandary M.
Associate Professor of Botany
Government College, Karwar – 581301
mbjaikar@gmail.com
GENE INTERACTIONS
(FOR BOTANY STUDENTS OF B. SC. SEMESTER VI, PAPER 1,
KARNATAKA UNIVERSITY, DHARWAD

2. 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-

3. 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.

4. INCOMPLETE DOMINANCE
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5. 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).

6. 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

7. 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?

9. 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

10. 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

11. 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

12. (CCpp
CCpp) (ccPP
ccPP)
White (CCpp) X White (ccPP)
F2: Purple 9 , White 7

13. 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.

14. 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).