Prepared for B. Sc. III Botany students, based on the syllabus prescribed by Dr. Babasaheb Ambedkar Marathwada University, Aurangabad.

1. B.SC. III: SEMESTER-VI
PAPER-XIX: GENETICS AND
BIOTECHNOLOGY
GENETIC INTERACTIONS
(A) NONEPISTATIC
DR. ANJALI NAIK
HEAD, DEPT. OF BOTANY, SBES COLLEGE
OF SCIENCE.

2. GENETIC
INTERACTIONS
• Two types of genetic interactions: Intra-allelic and inter-allelic or non-
allelic.
• Mendelian genetics is unable to explain all kinds of inheritance for
which the phenotypic ratios in some cases are different from
Mendelian ratios. An allele may be partially or equally dominant to
the other or due to existence of more than two alleles or there may
be present, lethal alleles.These kinds of genetic interactions between
the alleles of a single gene are referred to as allelic or intra- allelic
interactions.
• Non-allelic or inter-allelic interactions occur where the development
of single character is due to two or more genes affecting the
expression of each other in various ways.Thus, the expression of
gene is not independent of each other and dependent on the
presence or absence of other gene or genes;These kinds of
deviations from Mendelian one gene-one trait concept is known as
Interaction of Genes.

3. NON-ALLELIC NON-EPISTATIC GENETIC INTERACTIONS:
EXAMPLE- COMB SHAPE IN FOWLS
• The different varieties of chickens possess distinctive combs. For instance, Wyandottes have
a "rose" comb, Brahmas have a "pea" comb, and Leghorns have a "single" comb. In this case,
two non-allelic gene pairs affect the same character.
• The dominant allele of each of the two factors produces separate phenotypes when they are
alone. When both the dominant alleles are present together, they produce a distinct new
phenotype. The absence of both the dominant alleles gives rise to yet another phenotype.
• Two genes, R and P along with their recessive alleles determine the comb shapes. R gene
gives rise to rose comb and P gene gives rise to pea comb; both are dominant over single
comb; the presence of both the dominant genes results in walnut comb.

4. R- (Rose) > r (Single), P-(Pea) > p (single)
Parents: RRpp (Rose) X rrPP (Pea)
Gametes of parents: Rose combed parent- R and p;
and Pea combed parent: r and P
F1 : RrPp (Walut combed)------------------------- Selfed
RrPp X RrPp
Gametes of F1 : RP, Rp, rP, rp
F2 : Punnett square
Working out the genetic interaction for comb shapes in fowls

5. NON-ALLELIC, NON-EPISTATIC GENETIC INTERACTIONS
COMB SHAPE IN FOWLS

6. RRPP-1
RrPP-2
RRPp-2
RrPp-4
RRpp-1
Rrpp-2
rrPP-1
rrPp-2
Rrpp-1
9 - walnut
3-Rose
3- Pea
1- single
Genotypes, phenotypes and their proportions.
F2 : phenotypic ratio:

7. ASSIGNMENT QUESTIONS
1. In poultry, gene for Rose comb (R) and Pea comb (P) together produce Walnut comb. The recessive alleles
homologous for both these genes (rrpp) produce a condition of Single type of comb. Determine the proportion of
phenotypes expected from the following crosses.
• (a) RRPp X rrPp (d) RrPp X RrPP
• (b) RrPp X RrPp (e) RRPP X rrpp
• (c) rrpp X RrPp (f) Rrpp X rrPp
2. Note: As above-
• In a cross of Rose combed fowl with walnut combed fowl, the offspring appeared in the following proportion:
• Walnut ¾: Rose ¾: Pea ¼: Single ¼
• What are the genotypes of the parents?