Please explain In a Drosophila sexlinked cross a wild type m

Please explain

In a Drosophila sex-linked cross, a wild type male was mated to a white eye female. Their phenotypically wild F_1 female produced the following offspring when crossed to white eye males: Please set up a null hypothesis and use a Chi-square analysis to see if the observation follows the phenotypic ratio.

Solution

Wild type male X white eye female

F1 wild type female X white eye male

WT female 150

WT male 165

White eye female 170

White eye male 155

The normal phenotypic ratio must be 3:1 (expected)

But the observed ratio is almost 2:2

Chi-square = (O-E)²/E

= (2-3)²/3 + (2-1)²/1

= 1/3 + 1 = 4/3 = 1.33

Degrees of freedom is 2-1 =1

The critical value for 1 as degree of freedom is 3.8 from the table.

As the calculated chi-square value (1.33) is less than 3.8, the null hypothesis is accepted.

The observed ratio of the offsprings are accepted to appear in that way.