A variety of pure-breeding snapdragons produces a tall plant with green seeds (W

Question

A variety of pure-breeding snapdragons produces a tall plant with green seeds (WWSS). A second variety of pure-breeding snapdragons produce a short plant with white seeds (wwss). The two varieties are crossed, and the resulting seeds are collected. All of the seeds are green and when planted, they produce all tall plants (WwSs). These tall F1 plants are allowed to self-fertilize. The results for seeds and plant height in the F2 generations are as follows. What is the ?2 value, and the degrees of freedom for this experiment?

F2 Plant phenotype

Observed #

Green seed, tall

600

White seed, tall

175

Green seed, short

165

White seed, short

60

Total

1000

?2 = 6.1, df = 4

?2 = 6.1, df = 1

?2 = 0.4, df = 3

?2 = 0.4, df = 4

?2 = 6.1, df = 3

?2 = 0.4, df = 1

F2 Plant phenotype

Observed #

Green seed, tall

600

White seed, tall

175

Green seed, short

165

White seed, short

60

Total

1000

Explanation / Answer

Answer:    ?2 = 6.1, df = 3

Explanation:

During F2 generation of Dihybrid cross, progeny are produced in the following manner.

Both dominant phenotypes = 9/16 –green seed, tall

First dominant phenotype and second is recessive phenotype = 3/16—green seed, short

First recessive phenotype and second is dominant phenotype = 3/16---white seed, tall

Both recessive phenotypes = 1/16---white seed, short

X2 value = 6.1

Degrees of freedom = number of phenotype class -1 = 4-1 = 3

Phenotype Observed(O) Expected (E) O-E (O-E)2 (O-E)2/E green seed, tall 600 562.50 37.50 1406.25 2.50 green seed, short 165 187.50 -22.50 506.25 2.70 white seed, tall 175 187.50 -12.50 156.25 0.83 white seed, short 60 62.50 -2.50 6.25 0.10 Total 1000 1000.00 6.13

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