In Drosophila, singed bristles (sn) and carnation eyes (car) are both caused by
ID: 11907 • Letter: I
Question
In Drosophila, singed bristles (sn) and carnation eyes (car) are both caused by recessive alleles. The wild-type alleles (sn+ and car+) are responsible for straight bristles and red eyes, respectively. A sn+ car female is mated to a sn car+ male and the F1 progeny are testcrossed, resulting in the following distribution of offspring:
sn car 42
sn car+ 65
sn+ car 55
sn+ car+ 38
Total 200
What is the value of X2 for a test of the hypothesis that the sn and car genes are unlinked?
Explanation / Answer
sn car 42
sn car+ 65
sn+ car 55
sn+ car+ 38
Total 200
singed bristles (sn) and carnation eyes (car) are both caused by recessive alleles
alleles (sn+ and car+) are responsible for straight bristles and red eyes
sn+ car female x sn car+ male
offspring- sn+/sn car/ car+ -----------------F1
TEST CROSS
sn+/sn car/ car+ X sn/sn car/ car
EXPECTED RATIO------------------ 1:1:1:1
sn car+ 65
sn+ car 55
sn+ car+ 38
OBSEREVED (O)
EXPECTED(E)
O-E
(O-E)2
(O-E)2/E
sn car
42
50
-8
64
1.28
sn car+
65
50
-15
225
4.5
sn+ car
55
50
5
25
0.5
sn+ car+
38
50
-12
144
2.88
200
9.16
X2= SUM OF (O-E)2/E
What is the value of X2 for a test of the hypothesis that the sn and car genes are unlinked?
the value of X2 for a test of the hypothesis that the sn and car genes are unlinked= 9.16
IT IS MORE THAN THE TABLE VALUE, SO THE hypothesis IS REJECTED,
THE ALLES ATE LINKED
OBSEREVED (O)
EXPECTED(E)
O-E
(O-E)2
(O-E)2/E
sn car
42
50
-8
64
1.28
sn car+
65
50
-15
225
4.5
sn+ car
55
50
5
25
0.5
sn+ car+
38
50
-12
144
2.88
200
9.16