Question

R. C. Punnett conducted experiments on the inheritance of traits in the sweet pea, Lathyrus odoratus. In one experiment, he crossed two different true-breeding sweet pea plant strains, one with erect petals and long pollen, and the other with hooded petals and round pollen. All the offspring (F1F1 generation) had erect petals and long pollen (Figure 1).

Figure 1. Sweet pea plant cross

Next, Punnett allowed the F1F1 generation to self-fertilize and recorded the phenotypes of their offspring. The data are shown in Table 1.

Table 1. F2F2 results of F1F1 self-fertilization cross

Phenotype of F2F2	Number of Offspring
Erect petals, long pollen	765
Erect petals, round pollen	62
Hooded petals, long pollen	71
Hooded petals, round pollen	220
Total	1,118

How many degrees of freedom should be used when looking up the critical value for a chi-square analysis of the ratios of phenotypes observed among the F2F2 offspring versus the expected phenotypic ratio assuming independent assortment?

• 2

  A

• 3

  B

• 4

  C

• 5

Answer 1

Degrees of Freedom = N-1

where, N = total number of outcomes (here, phenotypes)

So, Degrees of Freedom = 4-1 = 3

Answer is B.3.