Download Linkage and Gene Mapping

Linkage and Gene Mapping (3 genes)
Gene Mapping in Corn
Is the gene for dwarf on the same chromosome as the gene for iojap and glossy?
Lines to work with:
Phenotype
Genotype
A: dwarf glossy (normal)
dd gg II
B: dwarf (normal)
iojap
dd GG ii
C: (normal) glossy iojap
DD gg ii
D: (normal) (normal) iojap
DD GG ii
E: (normal) (normal) (normal)
DD GG II
F: dwarf (normal) (normal)
dd GG II
What cross would you make to determine if the dwarf locus is linked to the glossy
locus?
Gene Mapping
What is the gene map (linkage map) for these three loci?
Lines to work with:
Phenotype
Genotype
A: dwarf glossy (normal)
dd gg II
B: dwarf (normal)
iojap
dd GG ii
C: (normal) glossy iojap
DD gg ii
D: (normal) (normal) iojap
DD GG ii
E: (normal) (normal) (normal)
DD GG II
F: dwarf (normal) (normal)
dd GG II
What cross would you need to make to determine the gene map?
Gene Mapping
Multiple Point Linkage Tests: More efficient means of mapping several linked
genes. Cross suitable genotypes that have different alleles at several gene
pairs.
So for these three genes on chromosome 4 of maize;
Inbred line parents
GGJJTT x
F1
ggjjtt
GgJjTt
Testcross
GgJjTt x ggjjtt
Dull, Normal, Pod
Dull, Normal, Regular
Dull, Japonica, Pod
Dull, Japonica, Regular
Glossy, Normal, Pod
Glossy, Normal, Regular
Glossy, Japonica, Pod
Glossy, Japonica, Regular
total
885
56
2
50
47
1
61
898
2000
Draw a Punnett square which represents this cross …
What step have we not completed?
Certain gametes from the heterozygote represent 2 exchanges between the most
distant loci, the double crossover class of gametes.
Freq
G_____J_____T
g_____ j______t
G_____i_____T
g_____J______t
2
1
These double crossover gametes represent two exchanges between G and T.
None have been included in our count for this distance. So we need to correct
for this.
GjT
gJt
2
1
3
x 2 = 6 more G-T exchanges.
so.. 6 + 214 = 220 / 2000 = 11 map units.
Therefore, adding in the double crossover gametes is a good double check to
make sure the map was assembled correctly from the three point test cross data.
Corn seed traits: C__ Red S__ plump
W__normal
cc white ss shrunken ww waxey
CCssWW
x
ccSSww
CcSsWw
Test cross progeny:
Red, shrunken, normal 2777
White, plump, waxey
Red, plump, waxey
2708
116
White, shrunken, normal 123
Red, shrunken, waxey
643
White, plump, normal
626
Red, plump, normal
White, shrunken, waxey
4
3
7000
x
ccsswww
C_ - red
cc - white
S_ - plump
ss - shrunken
CCssWW
x
W_ - normal
ww - waxy
ccSSww
CsW
F1
cSw
Parental Gametes
(no crossovers)
test cross progeny
C s
W
CsW
red, shrunken, normal
c S
w
cSw
white, plump, waxey
Single Crossover Gametes
test cross progeny
Between S and W
C s
W
CSw
c S
w
csW
red, plump, waxey
white, shrunken,
normal
Between C and S
C s
W
Csw
red, shrunken, waxey
c S
w
cSW
white, plump, normal
Double Crossover Gametes
test cross progeny
Between C and S and W
C s
W
CSW
red, plump, normal
c S
w
csw
white, shrunken, waxey
Let’s try another… Three
DDEEFF
Point Linkage test...that gives a little different result
X ddeeff
DdEeFf X ddeeff
Gamete from Heterozygote_____#
D E F
D E f
D e F
D e f
dE F
d E f
d e F
d e f
D to E
D to F
E to F