1. A plant geneticist is investing the inheritance of genes for bitter taste (Su
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Question
1. A plant geneticist is investing the inheritance of genes for bitter taste (Su) and explosive rind (e) in watermelon (Citrullus lanatus). Explosive rind is recessive and causes watermelons to burst when cut. Non-bitter watermelons are a result of the recessive genotype (susu). The geneticist wishes to determine if the genes assort independently. She performs a testcross between a bitter/nonexplosive hybrid and a plant homozygous recessive for both traits. The following offspring are produced: Bitter/nonexplosive Bitter/explosive Non-bitter/non-explosive Non-bitter/explosive 62 62 81 Calculate the chi-square value and also the chi-square of independence for the null hypothesis that the two genes assort independently. Calculate using a chi-square test and the chi-square test of independence. Give your answer to the nearest tenth.Explanation / Answer
Null hypothesis : The observed values are not deviating from mendilian dihybrid test cross ration i.e. 1:1:1:1.
Test static - Chisquare test
Category
Bitter nonexplosive
Bitter explosive
Non bitter non explosive
non bitter explosive
Total
Observed values (O)
88
62
62
81
293
Exptected Ratio (ER)
1
1
1
1
4
Exprected Values (E)
73.25
73.25
73.25
73.25
Deviation (O-E)
14.75
-11.25
-11.25
7.75
D^2
217.5625
126.5625
126.5625
60.0625
D^2/E
2.970137
1.727816
1.727816
0.819966
7.245734
X^2
7.245734
Degrees of freedom
4
-
1
3
Inference: The calculated chisquare value i.e. 7.24 is less than the table value i.e. 7.82 at 3DF and 0.05 probability. Hence the null hypothesis is accepted. Which means the genes assorted independently.
Category
Bitter nonexplosive
Bitter explosive
Non bitter non explosive
non bitter explosive
Total
Observed values (O)
88
62
62
81
293
Exptected Ratio (ER)
1
1
1
1
4
Exprected Values (E)
73.25
73.25
73.25
73.25
Deviation (O-E)
14.75
-11.25
-11.25
7.75
D^2
217.5625
126.5625
126.5625
60.0625
D^2/E
2.970137
1.727816
1.727816
0.819966
7.245734
X^2
7.245734
Degrees of freedom
4
-
1
3
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