Question

A researcher planted 160 seeds from an F2 cross of two hybrid purple flowered plants and got 123 purple flowered progeny and 37 white flowered progeny. What was the Chi- Square value for this result?

How do we find the expected value for this problem if we are given the observe value?

Answer 1

Chi square value = 0.3

In order to find the expected value, an assumption of purple flower colour dominance over white flower colour has to be made.

Step-by-step explanation:

First, we will assume that the purple flower trait is dominant over white flower trait, and that the alleles segregate according to Mendelian standard. Hence, the expected F2 phenotypic ratio will be 3:1.

In order to get the Chi square, the expected phenotype frequency will be calculated thus;

Expected frequency (E) for purple flowered plants = 3/4 x 160 = 120

Expected frequency (E) for white flowered plants = 1/4 x 160 = 40

Observed frequency (O) for purple flowered plants = 123

Observed frequency (O) for white flowered plants = 37

Chi square
`X^(2)` =
`(O - E)^(2)/E`

For the purple colour flower

`X^(2) = (123 - 120)^(2)/120`, which gives 0.075

For the white colour flower

`X^(2) = (37 - 40)^(2)/40`, which gives 0.225

Total
`X^(2)` = 0.075 + 0.225, which gives 0.3