You testcross a fly that is heterozygous for three genes, A, B, and C. The wild
ID: 10390 • Letter: Y
Question
You testcross a fly that is heterozygous for three genes, A, B, and C. The wild type allele is designated with a "+" and the mutant allele is designated with a lower case letter. Below are the results of your test cross:
Phenotype Observed
-------------------------------------
abc 300
-------------------------------------
+++ 300
-------------------------------------
ab+ 50
-------------------------------------
++c 50
-------------------------------------
a++ 125
-------------------------------------
+bc 125
-------------------------------------
a+c 25
-------------------------------------
+b+ 25
------------------------------------
1000
1. Using X2, test if the three genes are unlinked.
(a) What is the X2 value?
(b) What is the p value?
(c) Are these genes unlinked?
2. Draw the best map for these genes, include the map units.
3. Is there any interference? If so how much?
Explanation / Answer
+++ /abc heterozygous x abc /abc tester
Expected tarion form test cross 1:1:1:1:1:1:1:1
Phenotype
Observed
expected
Difference(o-e)
(o-e)2
(o-e)2 /e
abc
300
125
-175
30625
245
+++
300
125
-175
30625
245
ab+
50
125
-75
5625
45
++c
50
125
-75
5625
45
a++
125
125
0
0
0
+bc
125
125
0
0
0
a+c
25
125
-100
10000
80
+b+
25
125
-100
10000
80
100
740
1. Using X2, test if the three genes are unlinked.
(a) What is the X2 value?
X2 value=(o-e)2 /e = 740
It is higher than table value at 5% level of significance,
It deviated from the test cross ratio
It can concluded that the genes linked
Phenotype
Observed
expected
Difference(o-e)
(o-e)2
(o-e)2 /e
abc
300
125
-175
30625
245
+++
300
125
-175
30625
245
ab+
50
125
-75
5625
45
++c
50
125
-75
5625
45
a++
125
125
0
0
0
+bc
125
125
0
0
0
a+c
25
125
-100
10000
80
+b+
25
125
-100
10000
80
100
740
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