Linkage
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Linkage A testcross from a dihybrid cross can be illustrated as follows: P
AABB x aabb
F1
AaBb
A
B
A
B
A
B
a
b
a
b
a
b
Test-cross AaBb x aabb
A
B
a
b
X
X
a
b
a
b
A a
B b
A
B
a
b
A
b
a
B
X
X
a a
b b
Test Cross
a
b
Gametes
Test-cross progeny in 1 : 1 : 1 : 1 ratio A
B
a
b
a
b
a
b
A
b
a
b
a
B
a
b
50% of progeny have parental phenotype
50% of progeny have recombinant phenotype
A
B
a
b
A
B
X
X a
a
b
a
b
a
b
X
A
B
a
b
A
b
a
B
X
b
recombinant
Cross-over
A
B
A
b
a
b
a
b
a
b
a
B
a
b
a
b
› 50% with parental phenotype
recombinant
Test-cross progeny not in 1 : 1 : 1 : 1 ratio
‹ 50% with recombinant phenotype
Two-Factor Cross re red-eye
re+ wild-type
bz bronze-body
bz+ wild-type
P
rere/bzbz
F1
rere+/bzbz+
Test-cross
x
re+re+/bz+bz+
rere+/bzbz+ x rere/bzbz
re
bz
re
bz
re+
bz+
re+
bz+
rebz
(red-eye, bronze-body)
350
re
bz
re+bz+
(wild-type)
350
re+
bz+
rebz+
(red-eye)
150
re
bz+
re+bz
(bronze-body)
150
re+
bz
1000 Recombination percentage = (150 + 150)/1000 x 100% = 30% Map distance between re and bz = 30 map units
Cross A
Cross B
wild type purple/vestigial wild type purple/ebony P pr+pr+vg+vg+ x prprvgvg P pr+pr+e+e+ x prpree wild type purple/vestigial wild type purple/ebony TC pr+prvg+vg x prprvgvg TC pr+pre+e x prpree Wild type Purple eye/vestigial Normal eye/vestigial Purple eye/normal wing
162 158 39 41
Wild type 103 Purple eye/ebony 98 Normal eye/ebony 100 Purple eye/normal body 99
Observed •
Parental phenotype
Recombinant phenotype
320
80
Null hypothesis: Parental phenotype and recombinant phenotype is in 1 : 1 ratio.
•
Parental
Recombinant
Observed
320
80
Expected
200
200
∀ Χ2 = (320-200)2/200 + (80-200)2/200 = 72 + 72 = 144 •
From the Χ2 table, Χ2 at 5% level of confidence with 1 degree of freedom is 3.84.
•
The null hypothesis is rejected, the parental and recombinant phenotype does not fit the 1 : 1 ratio.
b black body
P
b+ vg+ bw+ b vg bw +
+
Test- cross
+
X
b vg bw
b+ gray body
b vg bw
vg vestigial
b+ vg+ bw+ b vg bw
Progeny b vg bw
225
b vg bw
220
b+ vg+ bw
89
b vg bw
86
b+ vg bw
80
b vg+ bw+
85
b+ vg bw+
7
b vg bw
8
+
+
+
+
+
X
}
b vg bw
vg+ normal wing
b vg bw
bw brown-eye
parental phenotype
bw+ red-eye
(no cross-over)
}
vg – bw cross-over
}
b – vg cross-over
}
double cross-over
800 Distance between vg - bw =
(89+86+7+8) 800
X 100 = 23.75
Progeny b+ vg+ bw+
225
b vg bw
} 220
b vg bw
89
b vg bw+
86
b+ vg bw
80
+
+
b vg bw
85
b+ vg bw+
7
b vg+ bw
8
+
+
parental phenotype
b+ gray body
(no cross-over)
}
b black body
vg vestigial
vg – bw cross-over
vg+ normal wing bw brown-eye
}
b – vg cross-over
}
double cross-over
800 Distance between vg - bw =
Distance between b – vg =
Distance between b – bw =
(89+86+7+8) 800 (80+85+7+8) 800
bw+ red-eye
x 100 = 23.75
x 100 = 22.50
89+86+80+85+2(7+8) 800
x 100 = 46.25
Genetic map or Linkage map
b
vg
22.50
bw
23.75
Chromosome interference (Chiasma interference) (7+8)
Observed double cross-over
=
Expected double cross-over
= 0.2250 x 0.2375 = 0.0534
Coefficient of interference
= 1 – coefficient of coincidence
Coefficient of coincidence
=
800
= 0.0187
Observed double cross-over Expected double cross-over
=
0.0185 0.0534
b black body
P
b+ vg+ bw+ b vg bw +
+
Test- cross
+
X
b vg bw
b+ gray body
b vg bw
vg vestigial
b+ vg+ bw+ b vg bw
X
b vg bw
vg+ normal wing
b vg bw
bw brown-eye bw+ red-eye
Progeny b+ vg+ bw+
225
b vg bw
220
b+ vg+ bw
89
b vg bw
86
b+ vg bw
80
b vg+ bw+
85
b+ vg bw+
7
b vg bw
8
+
+
800
}
parental phenotype (no cross-over)
}
vg – bw cross-over
}
b – vg cross-over
}
double cross-over
b black body
P
vg b bw+
X
vg b bw
+
Test- cross
vg+ b+ bw
b+ gray body
vg+ b+ bw
vg vestigial
vg b bw+ vg b bw +
+
X
vg b bw
vg+ normal wing
vg b bw
bw brown-eye bw+ red-eye
Progeny vg b bw+
225
vg b bw
220
vg b bw
89
vg b bw
86
vg+ b bw
80
vg b bw
85
vg b+ bw
7
vg b bw
8
+
+
+
+
+
+
+
+
+
800
} no cross-over } } } double cross-over
P
vg b bw+
X
vg b bw
+
Test- cross
vg+ b+ bw vg+ b+ bw
vg b bw+ X
vg b bw +
1
2
3
4
+
vg b bw+
225
vg b bw
220
vg b bw
89
vg+ b+ bw+
86
vg+ b bw
80
vg b+ bw+
85
vg b+ bw
7
vg b bw
8
+
+
+
+
vg b bw
800
vg b bw
} no cross-over
Phenotype No.
}
1.
vg+ b+
306
2.
vg b
314
}
3.
vg+ b
88
4.
vg b+
92
} double cross-over
P
vg b bw+
X
vg b bw
+
Test- cross
vg+ b+ bw vg+ b+ bw
vg b bw+ vg b bw +
Progeny vg b bw+
+
X
vg b bw vg b bw
225
vg b bw
no cross-over } 220
vg b bw
89
+
+
vg b bw
86
vg+ b bw
80
vg b bw
85
vg b+ bw
7
vg b bw
8
+
+
+
+
+
+
+
800
} } } double cross-over
A
B
C
a
b
c
A
B
C
a
b
c
A
b
C
a
B
c
b black body
P
b vg bw+ b vg bw
+
Test- cross
X
b+ vg+ bw
b+ gray body
b+ vg+ bw
vg vestigial
b vg bw+ b vg bw +
+
X
b vg bw
vg+ normal wing
b vg bw
bw brown-eye bw+ red-eye
Progeny b vg bw+
225
b+ vg+ bw
220
b vg bw
89
+
b vg bw
86
b vg+ bw
80
b+ vg bw+
85
b+ vg bw
7
b vg bw
8
+
+
+
+
800
}
parental phenotype (no cross-over)
}
vg – bw cross-over
}
b – vg cross-over
}
double cross-over
Progeny b vg bw+
225
b vg bw
} 220
b vg bw
89
b+ vg+ bw+
86
b vg+ bw
80
b vg bw
85
b+ vg bw
7
b vg+ bw+
8
+
+
+
+
parental phenotype
b+ gray body
(no cross-over)
}
b black body
vg vestigial
vg – bw cross-over
vg+ normal wing bw brown-eye
}
b – vg cross-over
}
double cross-over
800 Distance between vg - bw =
Distance between b – vg =
Distance between b – bw =
(89+86+7+8) 800 (80+85+7+8) 800
bw+ red-eye
x 100 = 23.75
x 100 = 22.50
89+86+80+85+2(7+8) 800
x 100 = 46.25
AABB x aabb
F1
AaBb
A
B
A
B
A
B
a
b
a
b
a
b
Test-cross AaBb x aabb
A
B
a
b
X
X
a
b
a
b
A a
B b
A
B
a
b
A
b
a
B
X
X
a a
b b
Test Cross
a
b
Gametes
Test-cross progeny in 1 : 1 : 1 : 1 ratio A
B
a
b
a
b
a
b
A
b
a
b
a
B
a
b
50% of progeny have parental phenotype
50% of progeny have recombinant phenotype
A
B
a
b
A
B
X
X a
a
b
a
b
a
b
X
A
B
a
b
A
b
a
B
X
b
recombinant
Cross-over
A
B
A
b
a
b
a
b
a
b
a
B
a
b
a
b
› 50% with parental phenotype
recombinant
Test-cross progeny not in 1 : 1 : 1 : 1 ratio
‹ 50% with recombinant phenotype
Two-Factor Cross re red-eye
re+ wild-type
bz bronze-body
bz+ wild-type
P
rere/bzbz
F1
rere+/bzbz+
Test-cross
x
re+re+/bz+bz+
rere+/bzbz+ x rere/bzbz
re
bz
re
bz
re+
bz+
re+
bz+
rebz
(red-eye, bronze-body)
350
re
bz
re+bz+
(wild-type)
350
re+
bz+
rebz+
(red-eye)
150
re
bz+
re+bz
(bronze-body)
150
re+
bz
1000 Recombination percentage = (150 + 150)/1000 x 100% = 30% Map distance between re and bz = 30 map units
Cross A
Cross B
wild type purple/vestigial wild type purple/ebony P pr+pr+vg+vg+ x prprvgvg P pr+pr+e+e+ x prpree wild type purple/vestigial wild type purple/ebony TC pr+prvg+vg x prprvgvg TC pr+pre+e x prpree Wild type Purple eye/vestigial Normal eye/vestigial Purple eye/normal wing
162 158 39 41
Wild type 103 Purple eye/ebony 98 Normal eye/ebony 100 Purple eye/normal body 99
Observed •
Parental phenotype
Recombinant phenotype
320
80
Null hypothesis: Parental phenotype and recombinant phenotype is in 1 : 1 ratio.
•
Parental
Recombinant
Observed
320
80
Expected
200
200
∀ Χ2 = (320-200)2/200 + (80-200)2/200 = 72 + 72 = 144 •
From the Χ2 table, Χ2 at 5% level of confidence with 1 degree of freedom is 3.84.
•
The null hypothesis is rejected, the parental and recombinant phenotype does not fit the 1 : 1 ratio.
b black body
P
b+ vg+ bw+ b vg bw +
+
Test- cross
+
X
b vg bw
b+ gray body
b vg bw
vg vestigial
b+ vg+ bw+ b vg bw
Progeny b vg bw
225
b vg bw
220
b+ vg+ bw
89
b vg bw
86
b+ vg bw
80
b vg+ bw+
85
b+ vg bw+
7
b vg bw
8
+
+
+
+
+
X
}
b vg bw
vg+ normal wing
b vg bw
bw brown-eye
parental phenotype
bw+ red-eye
(no cross-over)
}
vg – bw cross-over
}
b – vg cross-over
}
double cross-over
800 Distance between vg - bw =
(89+86+7+8) 800
X 100 = 23.75
Progeny b+ vg+ bw+
225
b vg bw
} 220
b vg bw
89
b vg bw+
86
b+ vg bw
80
+
+
b vg bw
85
b+ vg bw+
7
b vg+ bw
8
+
+
parental phenotype
b+ gray body
(no cross-over)
}
b black body
vg vestigial
vg – bw cross-over
vg+ normal wing bw brown-eye
}
b – vg cross-over
}
double cross-over
800 Distance between vg - bw =
Distance between b – vg =
Distance between b – bw =
(89+86+7+8) 800 (80+85+7+8) 800
bw+ red-eye
x 100 = 23.75
x 100 = 22.50
89+86+80+85+2(7+8) 800
x 100 = 46.25
Genetic map or Linkage map
b
vg
22.50
bw
23.75
Chromosome interference (Chiasma interference) (7+8)
Observed double cross-over
=
Expected double cross-over
= 0.2250 x 0.2375 = 0.0534
Coefficient of interference
= 1 – coefficient of coincidence
Coefficient of coincidence
=
800
= 0.0187
Observed double cross-over Expected double cross-over
=
0.0185 0.0534
b black body
P
b+ vg+ bw+ b vg bw +
+
Test- cross
+
X
b vg bw
b+ gray body
b vg bw
vg vestigial
b+ vg+ bw+ b vg bw
X
b vg bw
vg+ normal wing
b vg bw
bw brown-eye bw+ red-eye
Progeny b+ vg+ bw+
225
b vg bw
220
b+ vg+ bw
89
b vg bw
86
b+ vg bw
80
b vg+ bw+
85
b+ vg bw+
7
b vg bw
8
+
+
800
}
parental phenotype (no cross-over)
}
vg – bw cross-over
}
b – vg cross-over
}
double cross-over
b black body
P
vg b bw+
X
vg b bw
+
Test- cross
vg+ b+ bw
b+ gray body
vg+ b+ bw
vg vestigial
vg b bw+ vg b bw +
+
X
vg b bw
vg+ normal wing
vg b bw
bw brown-eye bw+ red-eye
Progeny vg b bw+
225
vg b bw
220
vg b bw
89
vg b bw
86
vg+ b bw
80
vg b bw
85
vg b+ bw
7
vg b bw
8
+
+
+
+
+
+
+
+
+
800
} no cross-over } } } double cross-over
P
vg b bw+
X
vg b bw
+
Test- cross
vg+ b+ bw vg+ b+ bw
vg b bw+ X
vg b bw +
1
2
3
4
+
vg b bw+
225
vg b bw
220
vg b bw
89
vg+ b+ bw+
86
vg+ b bw
80
vg b+ bw+
85
vg b+ bw
7
vg b bw
8
+
+
+
+
vg b bw
800
vg b bw
} no cross-over
Phenotype No.
}
1.
vg+ b+
306
2.
vg b
314
}
3.
vg+ b
88
4.
vg b+
92
} double cross-over
P
vg b bw+
X
vg b bw
+
Test- cross
vg+ b+ bw vg+ b+ bw
vg b bw+ vg b bw +
Progeny vg b bw+
+
X
vg b bw vg b bw
225
vg b bw
no cross-over } 220
vg b bw
89
+
+
vg b bw
86
vg+ b bw
80
vg b bw
85
vg b+ bw
7
vg b bw
8
+
+
+
+
+
+
+
800
} } } double cross-over
A
B
C
a
b
c
A
B
C
a
b
c
A
b
C
a
B
c
b black body
P
b vg bw+ b vg bw
+
Test- cross
X
b+ vg+ bw
b+ gray body
b+ vg+ bw
vg vestigial
b vg bw+ b vg bw +
+
X
b vg bw
vg+ normal wing
b vg bw
bw brown-eye bw+ red-eye
Progeny b vg bw+
225
b+ vg+ bw
220
b vg bw
89
+
b vg bw
86
b vg+ bw
80
b+ vg bw+
85
b+ vg bw
7
b vg bw
8
+
+
+
+
800
}
parental phenotype (no cross-over)
}
vg – bw cross-over
}
b – vg cross-over
}
double cross-over
Progeny b vg bw+
225
b vg bw
} 220
b vg bw
89
b+ vg+ bw+
86
b vg+ bw
80
b vg bw
85
b+ vg bw
7
b vg+ bw+
8
+
+
+
+
parental phenotype
b+ gray body
(no cross-over)
}
b black body
vg vestigial
vg – bw cross-over
vg+ normal wing bw brown-eye
}
b – vg cross-over
}
double cross-over
800 Distance between vg - bw =
Distance between b – vg =
Distance between b – bw =
(89+86+7+8) 800 (80+85+7+8) 800
bw+ red-eye
x 100 = 23.75
x 100 = 22.50
89+86+80+85+2(7+8) 800
x 100 = 46.25
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