EPISTASIS
GROUP 3
Epistasis in Greek word meaning standing over.
Epistasis is a phenomenon where the effect of one gene (Locus)
is dependent on the presence of one or more “modifier genes”
An interaction between a pair of loci, in which the phenotypic
effect of one locus depends on the genotype at the second locus.
Genes whose phenotype are
Expressed – EPISTATIC
Suppressed - HYPOSTATIC
DOMINANT
DUPLICATE
DUPLICATE
RECESSIVE
RECESSIVE
EPISTASIS
EPISTASIS
(COMPLEMEN
(COMPLEMENTARY
TARY GENES)
GENES)
RECESSIVE
EPISTASIS
DUPLICATE DOMINANT
EPISTASIS (DUPLICATE
GENES)
DOMINANT AND
RECESSIVE
EPISTASIS
(SUPPRESSOR
GENES)
DUPLICATE
GENES WITH
CUMULATIVE
EFFECTS
12:3:1
DUPLICATE
RECESSIVE
EPISTASIS
(COMPLEMEN
TARY GENES)
9:7
9:3:4
EPISTASIS
15:1
9:6:1
13:3GEN
ES)
EPISTASIS
Epistasis takes place when
the action of one gene is
modified by one or several
other genes, which are
sometimes called modifier
genes.
CONT…
The gene whose phenotype is expressed is said to be
Epistatic, while the phenotype altered or
suppressed is said to be Hypostatic.
DOMINANT EPISTASIS
12:3:1
A dominant epistasis is when
the dominant allele of one
gene hides the expression of
all alleles of another gene.
RECESSIVE
EPISTASIS (9:3:4)
A recessive epistasis
is when the recessive
allele of one gene
hides the expression
of all alleles of another
gene.
Here the homozygous
recessive allele (bb) for a gene
masks the expression of the
dominant allele (A-) for another
gene ("bb" suppress "A")
DOMINANT AND RECESSIVE
EPISTASIS (SUPPRESSOR
GENES) (9:3:4)
The dominant form of a
gene inhibits the expression
of another gene This socalled suppressor genes. A
dihybrid cross between two
heterozygous parents will
produce an F2 ratio of 13:3.
DUPLICATE RECESSIVE
EPISTASIS (COMPLEMENTARY
GENES) (9:3:4)
Involves two pairs of non-allelic
genes. When dominant forms of
both the genes involved in
complementary gene interaction
are alone have same phenotypic
expression. But, if they are
present in combination, yield
different phenotypic effect and
the results in a ratio of ( 9:7)
DUPLICATE DOMINANT
EPISTASIS (DUPLICATE GENES)
(15:1)
When a dominant allele at
either of two loci can mask the
expression of recessive
alleles at the two loci, it is
known as duplicate dominant
epistasis. In rice awn character
is controlled by two dominant
duplicate genes (A and B).
Presence of any of these two
alleles can produce awn.
● When a dominant allele at either of two loci can mask the
expression of recessive alleles at the two loci, it is known as
duplicate dominant epistasis. In rice awn character is controlled by
two dominant duplicate genes (A and B). Presence of any of these
two alleles can produce awn. The awnless condition develops only
when both these genes are in homozygous recessive state (aabb).
A cross between awned and awnless strains produced awned
plants in F1. Intermating of F1 plants produced awned and awnless
plants in 15:1 ratio in F2 generation. The allele A is epistatic to a/b
alleles and all plants having allele A will develop awn. Another
dominant allele B is epistatic to alleles a/b. An individual with these
allele also develop awn character.
DUPLICATE GENES WITH
CUMULATIVE EFFECTS
(9:6:1)
● Both the dominant non allelic alleles,
when present together, give a new
phenotype, but when allowed to express
independently, they give their own
phenotypic expression separately.
●
`
In the absence of any dominant allele,
the recessive allele is expressed.
In pigs 5 and s are allelic genes;
S - giving sandy colour
ss - giving white colour.
●
●
A non-allelic gene R also gives sandy
colour (same as S) but when both the
dominant genes interact together, they
give red colour.
P:
F1:
F2:
SSrr (sandy)
x
ssRR (red)
SR
SsRr (red)
Sr
sR
sr
SSRr
(red)
SsRR
(red)
SsRr
(red)
SsRr
(red)
Ssrr
(red)
SR
SSRR
(red)
Sr
SSRr
(red)
SSrr
(sandy)
sR
SsRR
(red)
SsRr
(red)
sr
SsRr
(red)
ssRr
Ssrr
(sandy) (sandy)
ssRr
ssRR
(sandy) (sandy)
ssrr
(white)
EPISTASIS
IN HUMANS
HAIR COLOR
Eumelanin: Blonde, brown, black hair
Pheomelanin: Red Hair
MCR1 gene: converts pheomelanin to eumelanin
The genes of pheomelanin and MCR1 interact with each
other to produce one single phenotype.
THANK
YOU!