Question

Tired of watering his garden, your instructor is attempting to grow desert plants. One such plant is Indian paintbrush. A yellow variant has shown up, and we would like to determine if this variant is a Mendelian trait. We have taken a pure breeding red plant and crossed it with a a pure breeding yellow plant. The resulting F₁ plants were red The F₁ were selfed and the F₂ data is presented below:

Red Flowers 266

Yellow Flowers 69

Perform a chi square analysis on this data using the following hypothesis:

The mode of inheritance for flower color in Indian paintbrush plants is simple Mendelian.

What is the calculated chi-square value? Round to three decimal places

Answer 1

Null hypothesis - red colour is dominant over yellow colour.

P0 : RR (red) × rr (yellow)

F1 : Rr (red)

F2 : Rr × Rr

Gametes	R	r
R	RR red	Rr red
r	Rr red	rr yellow

PR - 3 : 1

Total # progenies = 266 + 69 = 335

Expected # red progenies = 335 × 3/4 = 251.25

Expected # yellow progenies = 335 × 1/4 = 83.75

Chi square test -

Phenotype	#observed	#expected	(O-E)^2/E
Red	266	251.25	0.865
Yellow	69	83.75	2.59

Chi square value = 0.865 + 2.59 = 3.425

Degrees of freedom = 2 - 1 = 1

P value = 0.05 to 0.1

Null hypothesis accepted.

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