42
1 EPISTATIC INTERACTIONS
| Date post: | 15-Jul-2015 |
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Science |
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EPISTATIC
INTERACTIONS
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1. Complementary gene (9:7)
2. Duplicate gene (15:1)
3. Suppressor gene (13:3)
4. Additive gene (9:6:1)
5. Dominant epistasis (12:3:1)
6. Recessive epistasis (9:3:4)
Types
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Complementary gene
(9:7)
Production of one phenotype requires the presence ofdominant alleles of both the genes controlling thecharacter
C W
ccWC wwccww
Contrasting phenotype
Anyone of the two dominant gene is unable to produce thephenotype when alone
They complement each other to produce concernedphenotype when they are together
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5
Reginald Punnett (left) joined William Bateson (right) in 1903
6Sweet pea (Lathyrus odoratus)
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Duplicate gene
(15:1)
Characters governed by duplicate gene action aredetermined by two completely dominant genes
Duplicate gene action: The presence of a single dominantallele of any one of the two genes governing the traitproduce the dominantphenotype
W
wwcc Contrasting phenotype
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9
Endosperm colour in maize
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Seed coat colour of oat
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Floating habit of rice
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Suppressor gene
(13:3)
The gene don’t directly cause the expression of thecharacters but suppress the expression of other genes
Example
Leaf colour of rice: Green Purple
Gg
I suppress G iIneffective
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Leaf colour of rice
Additive gene/ Polymeric genes/ Duplicate gene with cumulative effect
9:6:1
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Two completely dominant genes controlling a character
R W
R W
But both genes are present together, their phenotypiceffect is enhanced as the effect of the two geneswere cumulative additive
R W
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It produces identical phenotypes when they are alone
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Seed colour of wheat
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R_B_
rrbb
R_bbrrB_
Red colour in wheat is produced by the genotype R_B_, whiteby the double recessive genotype, rrbb. The genotypes R_bband rrB_ produce brown kernels. If homozygous red varietyis crossed to a white variety what phenotypic results areexpected in the F1 and F2?
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RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square
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RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square
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RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square
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RB Rb rB rb
RB RRBB
Red
RRBb
Red
RrBB
Red
RrBb
Red
Rb RRBb
Red
RRbb
Brown
RrBb
Red
Rrbb
Brown
rB RrBB
Red
RrBb
Red
rrBB
Brown
rrBb
Brown
rb RrBb
Red
Rrbb
Brown
rrBb
Brown
rrbb
White
Punnett Square for F2
Phenotypic ratio of F2 generation is Red: Brown: White = 9:6:1
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Dominant epistasis
12:3:1
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The two genes affecting the character W Y
When both genes are present in recessive state adifferent phenotype is produced
They produce distinct phenotype when they are alone
W Y
But when the genes are present together, the expressionof one gene masks the expression of other
YW
w y25
Fruits of Cucurbita pepa will be in green, yellow and whitecolour. White is dominant over both yellow and green butyellow is dominant over green only. White colour isdetermined by the dominant gene W and no other gene forfruit colour can be expressed in its presence. Thusdominant W is epistatic to two other fruit colour. In thepresence of homozygous recessive, ww another gene Ydetermine the yellow colour. Homozygous recessive plantsfor both genes, wwyy bears green fruit that the classicalratio the first two classes of a dihybrid ratio arephenotypic ally similar
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Fruit colour of Cucurbita pepa
wwyy
W_ _ _
ww Y_
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When homozygous white fruit seeds are crossed withhomozygous green fruit seeds, the F1 is all white. Crossingwith F1 among themselves F2 produced 121 white, 28 yellowand 9 green. Explain the results
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WY Wy wY wy
WY WWYY
White
WWYy
White
WwYY
White
WwYy
White
Wy WWYy
White
WWyy
White
WwYy
White
Wwyy
White
wY WwYY
White
WwYy
White
wwYY
Yellow
wwYy
Yellow
wy WwYy
White
Wwyy
White
wwYy
Yellow
wwyy
Green
Punnett Square
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WY Wy wY wy
WY WWYY
White
WWYy
White
WwYY
White
WwYy
White
Wy WWYy
White
WWyy
White
WwYy
White
Wwyy
White
wY WwYY
White
WwYy
White
wwYY
Yellow
wwYy
Yellow
wy WwYy
White
Wwyy
White
wwYy
Yellow
wwyy
Green
Punnett Square
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WY Wy wY wy
WY WWYY
White
WWYy
White
WwYY
White
WwYy
White
Wy WWYy
White
WWyy
White
WwYy
White
Wwyy
White
wY WwYY
White
WwYy
White
wwYY
Yellow
wwYy
Yellow
wy WwYy
White
Wwyy
White
wwYy
Yellow
wwyy
Green
Punnett Square for F2
Phenotypic ratio of F2 generation is White: Yellow: Green = 12:3:132
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Recessive epistasis
9:3:4
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In this gene interaction, the dominant allele of one geneproduces a phenotypic effect
The dominant allele of the other gene does not produce any phenotypic effect
But when it is present with dominant allele of the firstgene, it modifies the phenotypic effect produced by thefirst gene
C A
C A
C ACA CA
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Coat colour of mice
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The coat colour of mice is control by two genes C and A
C alone determine black colour but due to supplementary effect of A the colour is become black
C_A_
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When only gene C is homozygous recessive albino mice are produce
cc_ _
A alone has no effect
C_ aa
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Mating between black mice of identical genotype produced
offspring as follows; 14 Gray, 47 Black and 19 Albino.
1. What epistastic ratio is approximated by these offspring?
2. What are the phenotypes of the parents and offspring?
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CA Ca cA ca
CA CCAA
Black
CCAa
Black
CcAA
Black
CcAa
Black
Ca CCAa
Black
CCaa
Gary
CcAa
Black
Ccaa
Gray
cA CcAA
Black
CcAa
Black
ccAA
Albino
ccAa
Albino
ca CcAa
Black
Ccaa
Gray
ccAa
Albino
Ccaa
Albino
Punnett Square for F2
Phenotypic ratio is Black: Gray: Albino= 9: 3: 4
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Summary of epistatic interaction
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Thank you
