Question

A genetic researcher wanted to verify whether a heterozygote cross will yield a classic 3:1 phenotypic ratio. After crossing two heterozygote plants, the researcher noted phenotypes of the progeny. Observed phynotypes: 115 plants exhibited the dominant phenotype, and 35 plants exhibited the recessive phenotype. Does this result match the expected 3:1 phenotypic ratio in the F2 generation?

State the Ho and Ha hypothesis

what is the expected numbers of the dominant and recessive phenotypes

what is the DF. (95% confidence level)

What is the critical value to compare X^2 against.

Answer 1

1. H_o or Null hypothesis states that the population frequencies are equivalent to the expected frequencies.

Whereas, H_a or Alternative hypothesis states that the Null hypothesis is wrong.

2.

	Observed [O]	Expected [E]	[O-E]	[O-E]2	[O-E]2/ [E} or 2
Dominant	115	0.75 X 150 = 112.5	2.5	6.25	0.055
Recessive	35	0.25 X 150 = 37.5	-2.5	6.25	0.166
Total	150				0.221

3. Degree of freedom = n-1

Here, n means number of traits. So, according to question, value of n is 2; because there are two traits- dominant and recessive.

Degree of freedom = 2-1 = 1

4. Critical value of ² at 95% confidence level (found using standard table) = 0.004

Calculated value of ² = 0.221

Thus, calculated ² > observed ²

Therefore, Null hypothesis is rejected.