You cross two pure-breeding pea plants, one homozygouse dominant for both traits

ID: 32599 • Letter: Y

Question

You cross two pure-breeding pea plants, one homozygouse dominant for both traits (yellow and smooth) and the other homozygous recessive for both traits. You then self-fertilize the F1 generation. This produces 599 plants with yellow and smooth peas, 171 with green and smooth peas, 72 with wrinkled and green peas, and 158 with wrinkled and yellow peas. Does this fit with what you expected to produce in the F2 generation? A. Calculate the chi-square value to test your hypothesis. B. Are the observed ratios consistent with the expected?

Explanation / Answer

Based on your data,

Homozygous dominant genotype YYWW

Homozygous recessive genotype yyww

The yellow character is dominant over green and smooth dominant over wrinkled. The F1 gamete is YyWw (yellow and smooth). Then we self-fertilize F1 YyWw × YyWw results,

Based on the given observed results the ratio is: 9: 3: 3: 1 Yes, this fit with expected to F2 generation ratio.

A) Chi-square test:

Phenotypes

Actual numbers

Expected numbers

(o-e)

(o-e)2

(o-e)2/ e

Yellow and smooth peas

599

0.5 x 599 = 300

-299

89401

298

Green and smooth peas

171

0.1 x 171
= 17

-154

23716

1394

Wrinkled and green peas

0.07 x 72 = 6

-66

4356

726

Wrinkled and yellow peas

158

0.1 x 158 = 111

-47

2209

Total

1000

Chi-square critical value =2437

The degrees of freedom is (3-1) = 2

Thus, the Cumulative probability: P(2< CV) = 1.