Question

In sweet pea plants, the trait for purple flowers (P) is dominant to the trait for red flowers (p).
Similarly, the trait for long pollen (L) is dominant to the trait for round pollen (l).
Two F1 heterozygotes are self-crossed, yielding the following frequencies for the F2 generation:
296 purple, long plants ; 19 purple, round plants ; 27 red, long plants ; 85 red, round plants
Use the chi-squared test (α = 0.05) to determine if these results are due to independent assortment (9:3:3:1).

Answer 1

Given:

Frequencies of F2 generation as follows

296 purple, long plants

19 purple, round plants

27 red, long plants

85 red, round plants

To find:

Whether these results are due to independent assortment

Solution:

We will use the chi-squared test on the given dihybrid cross.

Given that purple flowers (P) is dominant to the trait for red flowers (p) and the trait for long pollen (L) is dominant to the trait for round pollen (l).

If the traits are independent from one another the ratio of PPLL : PPLl : PpLL : ppll = 9 : 3 : 3 : 1

In the given data,

PPLL = 296

PPLl = 19

ppLL = 27

ppll= 85

Thus the ratio = 296:19:27:85

This ratio shows a large deviation from the expected ratio.

Hence, the two traits i.e. flower color and pollen length are linked with each other.