German abbot Gregor Mendel published his famous pea results in 1866, to what can
ID: 272762 • Letter: G
Question
German abbot Gregor Mendel published his famous pea results in 1866, to what can be described as a general shrug. Fast forward 35 year when two scientists, Hugo de Vries and Carl Correns, independently arrived to the same conclusions and rediscovered his work. This would catch the general attention and eventually redefined the fields of genetics, evolutionary biology, and population genetics.
In 1904, William Bateson, Edith Saunders, and Reginald Punnett (of the Punnett square fame) published odd results: when selfing pea plants investigating pollen shape and flower color, the F2 generation deviated dramatically from the Mendelian 9:3:3:1 ratio expected of the F2 generation looking at 2 traits:
Discuss how and why those numbers deviate from Mendelian expectations (i.e is there any pattern of divergence in the data ?; what might be causing this divergence?) Why are these surprising or not surprising? Note that purple flowers and long pollen are the dominant phenotypes, while red flowers and round pollen are recessive.
Phenotype Observed Expected Purple, long 1528 1199 Purple, round 106 400 Red, long 117 400 Red, round 381 133 Total 2132 2132Explanation / Answer
Null Hypothesis: 1:1:1:1
Alternative Hypothesis: 9:3:3:1
Calculation:-
Phenotype
Observed(O)
Expected(E)
(O-E)
(O-E)2
(O-E)2/E
?2
Purple, long
1528
1199
329
108241
90.276
969.024
Purple, round
106
400
-294
86436
216.090
Red, long
117
400
-283
80089
200.222
Red, round
381
133
248
61504
462.436
Total
2132
2132
Degrees of freedom: 4-1 = 3
Critical value: The table value of chi-square for 3df at 0.05 is 7.82.
As calculated value of Chi-square for 3 df 969.024< critical value 7.82, so null hypothesis re rejected, i.e there is significant difference between the observed and expected result. So, here alternative hypothesis is accepted.
These are not surprising.
Phenotype
Observed(O)
Expected(E)
(O-E)
(O-E)2
(O-E)2/E
?2
Purple, long
1528
1199
329
108241
90.276
969.024
Purple, round
106
400
-294
86436
216.090
Red, long
117
400
-283
80089
200.222
Red, round
381
133
248
61504
462.436
Total
2132
2132
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