all types of gene action complementry epistatic

3. …….
Assignment no 1
ARRANGED BY; ; ; ZOHAIB HUSSAIN AND SAAD IQBAL
TOPIC ; ; ; ;
EPISTATIC INTERACTIONS
SUBMITTED TO:::;;;;;DR SARFARZ SHAFIQ
COURSE TITLE ; ; ; ; ; ;ESSENTIAL OF GENETICS

4. •Epistatic Gene
Interactions

5. Epistatic Gene Interactions
• Gene interactions occur when two or more different
genes influence the outcome of a single trait
• Most morphological traits (height, weight, color) are
affected by multiple genes
• Epistasis describes situation between various alleles
of two genes
• Quantitative loci is a term to describe those loci
controlling quantitatively measurable traits
• Pleiotropy describes situations where one gene affects
multiple traits

6. • examine cases involving 2 loci (genes) that each
have 2 alleles
• Crosses performed can be illustrated in general by
– AaBb X AaBb
– Where A is dominant to a and B is dominant to b
• If these two genes govern two different traits
– A 9:3:3:1 ratio is predicted among the offspring
– simple Mendelian dihybrid inheritance pattern
• If these two genes do affect the same trait the
9:3:3:1 ratio may be altered
– 9:3:4, or 9:7, or 9:6:1, or 8:6:2 or 12:3:1, or 13:3, or 15:1
– epistatic ratios

7. A Cross Producing a 9:7 ratio
Figure 4.18
9 C_P_ : 3 C_pp :3 ccP_ : 1 ccpp
purple
white

9. Epistatic Gene Interaction
• Complementary gene
action
Enzyme C and enzyme P
cooperate to make a
product, therefore they
complement one another

11. Epistatic Gene Interaction
• Epistasis describes the situation in which
a gene masks the phenotypic effects of
another gene
• Epistasis interactions arise because the
two genes encode proteins that
participate in sequence in a biochemical
pathway
• If either loci is homozygous for a null
mutation, none of that enzyme will be
made and the pathway is blocked

12. Colorless
precursor
Enzyme C
Colorless
intermediate
Enzyme P
Purple
pigment
genotype cc
Colorless
precursor
Enzyme C
Colorless
intermediate
Enzyme P
Purple
pigment

13. Epistasis of Involving Sex-linked Genes
• Inheritance of the Cream-Eye allele in
Drosophila
– a rare fly with cream-colored eyes identified
in a true-breeding culture of flies with eosin
eyes
– possible explanations
• 1. Mutation of the eosin allele into a
cream allele
• 2. Mutation of a 2nd gene that modifies
expression of the eosin allele

14. – Cream-colored eyes in fruit flies are due to
the effect of a second gene that modifies
the expression of the eosin allele

15. Testing the Hypothesis

17. Data obtained
Cross
Outcome
P cross:
Cream-eyed male X
wild-type female
F1: all red eyes
F1 cross:
F1 brother X F1 sister
F2: 104 females with red eyes
47 males with red eyes
44 males with eosin eyes
14 males with cream eyes
F2 generation contains males with eosin eyes
This indicates that the cream allele is
not in the same gene as the eosin allele

18. Interpreting the Data
Cross
Outcome
P cross:
Cream-eyed male X
wild-type female
F1: all red eyes
F1 cross:
F1 brother X F1 sister
F2: 104 females with red eyes
47 males with red eyes
44 males with eosin eyes
14 males with cream eyes
F2 generation contains –
151 + eye: 44 we eye: 14 ca eye
a 12 : 3 : 1 ratio

19. Modeling the Data


Cream phenotype is recessive therefore the
cream allele is recessive allele (either sexlinked or autosomal)
The mutated allele of the cream gene modifies
the we allele, while the wt cream allele does
not

C = Normal allele


Does not modify the eosin phenotype
ca = Cream allele

Modifies the eosin color to cream, does not effect wt or
white allele of white gene.

20. Male gametes
CXw+
CY
caXw+
caY
Female gametes
CXw+
CCXw+Xw+
CCXw+Y
cacaXw+Xw+
CcaXw+Y
CXw-e
CCXw+Xw-e
CCXw-eY
CcaXw+Xw-e
CcaXw-eY
caXw+
CcaXw+Xw+
CcaXw+Y
cacaXw+Xw+
cacaXw+Y
caXw-e
CcaXw+Xw-e
CcaXw-eY
cacaXw+Xw-e
cacaXw-eY

21. A Cross Involving a Two-Gene Interaction Can
Still Produce a 9:3:3:1 ratio
• Inheritance of comb morphology in chicken
– First example of gene interaction
– William Bateson and Reginald Punnett in 1906
– Four different comb morphologies

24. N

25. Figure 4.17b
The crosses of Bateson and Punnett

26. • F2 generation consisted of chickens with four
types of combs
– 9 walnut : 3 rose : 3 pea : 1 single
• Bateson and Punnett reasoned that comb
morphology is determined by two different
genes
– R (rose comb) is dominant to r
– P (pea comb) is dominant to p
– R and P are codominant (walnut comb)
– rrpp produces single comb

27. Gene Interaction
• Duplicate gene action
– Enzyme 1 and enzyme 2 are
redundant
– They both make product C,
therefore they duplicate each
other

28. x
Duplicate Gene
Action Epistasis
TTVV
Triangular
ttvv
Ovate
F1 generation
TtVv
All triangular
F1 (TtVv) x F1 (TtVv)
15:1 ratio results
TV
TV
Tv
tV
tv
Tv
tV
tv
TTVV
TTVv
TtVV
TtVv
TTVv
TTvv
TtVv
Ttvv
TtVV
TtVv
ttVV
ttVv
TtVv
Ttvv
ttVv
ttvv
(b) The crosses of Shull

29. Bombay Phenotype

30. Bombay Phenotype

31. Bombay Phenotype

34. Squash Fruit Color
• Genotypes and
Phenotypes:
• W-/G-
white
• W-/gg
white
• ww/G-
green
• ww/gg
yellow

35. Dominant Epistasis
• LETS HAVE A LOOK AT DOMINANT
EPISTASIS…
• Squash fruit color is controlled by two genes.
• Gene 1 is represented by a W
• Gene 2 is represented by a G

36. Squash Fruit Color
• Which allele is epistatic in squash color?
The dominant W allele is epistasis
• How do you know?
Because every time a dominant W allele
shows up in a squash genotype, the squash
fruit color is white.

37. Wwgg x wwGg
• FOIL: Wg or wg
• FOIL: wG or wg
• F1 generation genotypes:
• Phenotypes:

38. ....THANK..
……
YOU…..

39. REFRENCE BOOKS
•CELL BIOLOGY, GENETICS
•EPISTASIS AND
EVOLUTIONARY PROCESS BY
JASON WOLF
•COMBINATORIAL APPROACH
TO EPISTATIS BY R LOWEN
•CELL BIOLOGY AND GENETICS
BY S.CHAND