Download Testcross - dihybrid x recessive homozygous

Testcross - dihybrid x recessive homozygo
Independent assortment
AaBb X aabb
Progeny ¼ AaBb
¼ Aabb
¼ aaBb
¼ aabb
Perfect linkage
AaBb X aabb
Progeny ½ AaBb
cis
½ aabb
or
½ aaBb
trans ½ Aabb
Deviations from independent assortment
P
F1
pr/pr vg/vg
X
pr+/pr+ vg+/vg+
pr+/pr vg+/vg
dihybrid
Testcross
pr+/pr vg+/vg X pr/pr vg/vg
F1 dihybrid
Tester male
female
Progeny pr+ vg+ 1339
pr vg
1195
pr+ vg
151
pr vg+
154
Total
2839
Distance separating two genes is directly proportional to % of
total recombinants
Total recombinants
pr+ vg 151
pr vg+ 154
305 flies
Total progeny 2839 flies
Total recombinants/total progeny X 100 = % recombination
305/2839 X 100 = 10.7%
1% recombination = 1 map unit (mu, cm)
pr
10.7mu
vg
Linkage and recombination in the X chromosome
Test cross
b+/b vg+/vg X b/b vg/vg
Progeny
283 grey, normal
1,294 grey, vestigial
1,418 black, normal
241 black, vestigial
__________________
3,236 flies
Total
Adding genes to your map
From 1st testcross
From 2nd testcross
AaBb X aabb
a
5mu
b
AaCc X aacc
a 3mu c
Two possible arrangements c 3mu a
b
a 3mu c
Which one?
5mu
2mu b
Do the following cross: CcBb X ccbb
OR
Make a three point cross
Three point cross
Double crossovers can be used to determine order of ge
Double crossover
Relative gene position
Coincidence and Interference
Calculate expected frequency of DCOs
Multiply the frequency of recombination in region I by the frequen
recombination in region II
Calculate observed frequency of DCOs
from your experimental results
Coefficient of coincidence = observed DCOs/expected DC
Interference = 1- Coefficient of Coincidence
Coefficient of Coincidence =
Observed frequency of DCO
Expected frequency of DCOs
Observed frequency of DCOs = 6/500 0.012
Expected frequency of DCOs = Frequency COs region I x COs region
Frequency CO region I = 0.208
Frequency CO region II = 0.10
Expected frequency of DCOs = 0.208 x 0.10 = 0.0208 (0.02)
Coefficient of Coincidence = 0.012/0.02 = 0.6
Interference = 1 – Coefficient of Coincidence
Interference = 1 – 0.6 = 0.4
A female fruit fly heterozygous for the genes y (yellow body),
w (white eyes), and ec (echinus eyes) located on the X chrom
is mated to a yellow, white, echinus male. The phenotypes of
progeny are:
Phenotype
y w ec
y+ w+ ec+
y w+ ec+
y+ w ec
y w ec+
y+ w+ ec
y w+ ec
y+ w ec+
Number of flies
4685
4759
80
70
193
207
3
3
Total
10,000 flies
Determine: order of the genes, distance between genes, coin
and interference
Evidence of chromosomal exchange - corn
C = colored seeds
C = colorless
Wx = normal
wx = waxy
Evidence of chromosomal exchange - c
Evidence for
chromosome
exchange – Drosophila
Evidence for sister chromatid exchange in mitotic chromosomes
Sexual reproduction of an ascomycete
Neurospora
Three different patterns of ascospores and
how they are generated