The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. O

Question

The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true?
1) Since 48 is so close to the expected value, there is no need to calculate chi square before drawing a conclusion about the ratio.
2) At least one additional cell must also contain a count of 48.
3) The value of observed - expected for this cell = -2.
4) The progeny of this cross do not conform to a 1:1:1:1ratio.

Explanation / Answer

The expected ratio of phenotypes among the progeny of a test cross is 1:1:1:1. Out of 200 total resulting progeny, 48 occur in one of the four phenotypic classes. Given this information, which of the following must also be true?
1) Since 48 is so close to the expected value, there is no need to calculate chi square before drawing a conclusion about the ratio.
2) At least one additional cell must also contain a count of 48.
3) The value of observed - expected for this cell = -2. -correct
4) The progeny of this cross do not conform to a 1:1:1:1ratio.

chi square formula = (observed - expected )^2 /expected

observed - expected =48-50=-2

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