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

Answer:

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.

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