Question

For her science fair project, your little sister replicated one of Mendel's experiments. From a P0 pea plant with purple flowers and a pea plant with white flowers, she got 1 purple F1 hybrid (she had forgotten to water, so just one survived). From this self-fertilized F1 she got 8 F2 offspring. 7 were purple and 1 was white, for a 7:1 ratio. Did your little sister just disprove Mendel's laws

Answer 1

Answer: No, the 7:1 ratio is close to the expected 6:2 ratio even with the limited sample size.

Explanation:

Let the alleles be P (purple) and W (white).

The possible crosses are

PP x WW, PP x PW, PW x WW, PW x PW

the F1 is PP or PW

one F2 is white so the F1 must be PW and

the F2 are PP, WW, PW and

the expected 8 progeny are 2PP, 2WW, 4PW

Because 7/8 are purple, we can infer that P is dominant and W recessive, so the expectation is 6 purple, 2 white

The observed ratio is similar to the expected ratio, so we can’t say that this result disproves Mendel, particularly with a small sample.