Transcript epistasis examples

Recessive Epistasis
Complete dominance at both loci, but homozygous recessive condition at
one of the two loci is epistatic to the other.
Flower Colour in blue-eyed Mary (Collinsia parviflora)
wwMM
x
White
Magenta
WwMm
Blue
F1
F2
WWmm
WM
Wm
wM
wm
WM
WWMM
WWMm
WwMM
WwMm
Wm
WWMm
WWmm
WwMm
Wwmm
wM
WwMM
WwMm
wwMM
wwMm
wm
WwMm
Wwmm
wwMm
wwmm
9 Blue : 3 Magenta : 4 White
Also Agouti : Black : Albino coat colour in mice
Recessive Epistasis
Complete dominance at both loci, but homozygous recessive condition at
one of the two loci is epistatic to the other.
Enzyme 1 (w) is
epistatic to
Enzyme 2 (m)
Duplicate Dominant Epistasis
Example: Seed capsule shape in Shepherd's purse (Capsella bursa-pastoris)
Plant 1 has a heart–shaped seed capsule and Plant 2 has a narrow capsule
Crossing the two produces an F1 with a heart-shaped capsule
x
Single Dominant Gene?
Selfing the F1 produces the following F2 ratio: 15 heart to 1 narrow fruit
Duplicate Dominant Epistasis
Example: Seed capsule shape in Shepherd's purse (Capsella bursa-pastoris)
AABB
Heart Shape
aabb
Narrow Shape
AaBb
Heart Shape
F1
F2
x
AB
Ab
aB
ab
AB
AABB
AABb
AaBB
AaBb
Ab
AABb
AAbb
AaBb
Aabb
aB
AaBB
AaBb
aaBB
aaBb
ab
AaBb
Aabb
aaBb
aabb
A Dominant allele at either of the two loci produces a heart-shaped fruit
A is epistatic to B or b and B is epistatic to A or a to give a 15:1 ratio
Dominant Suppression Epistasis
Example: Malvidin production in Primula (anthocyanin giving blue flower)
Plants 1 and 2 lack blue pigment in their flowers.
When crossed together, the F1 also lacks pigment
Selfing the F1 produces blue flowered segregants
Phenotypic ratio: 13:3; Not 3:1
Dominant Suppression Epistasis
Example: Malvidin production in Primula (anthocyanin giving blue flower)
KKDD
Non blue
kkdd
Non blue
KkDd
Non Blue
F1
F2
x
KD
Kd
kD
kd
KD
KKDD
KKDd
KkDD
KkDd
Kd
KKDd
KKdd
KkDd
Kkdd
kD
KkDD
KkDd
kkDD
kkDd
kd
KkDd
Kkdd
kkDd
kkdd
Malvidin production controlled by dominant allele at K locus but the pathway is
blocked by a dominant allele at the suppressor locus D
Produces a 13 : 3 ration, like feather colour in chickens
Bell Pepper Colour Genetics
prepared by Dr. Paul Kusolwa
Two genes without Epistasis - Additive
Example: Fruit colour in Bell Pepper
CCrr
Yellow
ccRR
Brown
CcRr
Red
F1
F2
x
CR
Cr
cR
cr
CR
CCRR
CCRr
CcRR
CcRr
Cr
CCRr
CCrr
CcRr
Ccrr
cR
CcRR
CcRr
ccRR
ccRr
cr
CcRr
Ccrr
ccRr
ccrr
A Dominant allele at either of the two loci produces red fruit
Dominant alleles at the C locus and no dominant alleles at R give yellow fruit
Dominant alleles at the R locus and no dominant alleles at C give brown fruit
Double recessive gives green fruit
9:3:3:1
Fruit shapes in squash
Di locus
Dominant to spherical or pyriform
Duplicate genes with cumulative effects
When Di is present together with Spherical S
locus Di is dominant = Disc fruits
9 Discs
Di_S_
When Di present with recessive s = spherical fruits
When didi/ss = long or pyriform fruits
Modified Ratio = 9: 6: 1
6 Spherical = Di/s & di/S_
1 Pyriform di/s
Duplicate Recessive - Squash
Pathway involving two genes
Wt = warty fruits Dominant to
non warty wt
Hr = hard rind
hr = intermediate texture
9:7
B_
Hr_
Wt_
Y_
More Epistasis in Squash
Bicolor fruits = locus B pleiotropic for fruits and
leaves
For yellow and green color patches BB or Bb
Extent of yellow or green:
Model with 2 incompletely dominant
additive loci, Ep1 and Ep 2, proposed
for enlarging the yellow patches
Genotypes
Bb with a dosage of 0 to 1 Ep alleles
= bicolor green and yellow fruits
Dosage of 2-4 dominant Ep alleles
extends the yellow coloration
Genotypes
9 B_Ep_ Extended yellow
3 B_epep Yellow narrow
3 bbEp_ Green extended
1bbepep green
Tri-Genic Interactions….
Three or more genes interactions in ornamental gourds
Gb = green bands; gb for no bands
Gr/G = green rind (gr/g buff skin)
L-2 = color intensity (yellow /orange)
Gr
Gb
L-2
Ep-1/2