In guinea pigs white coat w is recessive to black coat W and

In guinea pigs, white coat (w) is recessive to black coat (W) and wavy hair (v) is recessive to straight hair (V). A guinea pig that is black with straight hair but has an unknown genotype is crossed with guinea pigs having white coats and wavy hair in a series of test crosses. The following progeny are produced from these testcrosses: 30 Black, straight; 10 Black, wavy; 12 White, straight: and 31 White, wavy. What is the genotype of the unknown parental guinea pig? If these genes are segregating independently, what is the expected phenotypic ratio for the cross? Support your assertion with a Punnett square. Use the chi square test to determine if the genes that determine coat color and hair type are segregating independently? Make a hypothesis that explains your results.

Solution

Null hypothesis: Ho: The population is assorting independently.

Alternate hypothesis: H1: The population is not assorting independently.

The cross is:

W_V_ crossed to wwvv. Result is

Please note that test cross expected phenotypic ratio should be 1:1:1:1 in case of independent assortment (part ‘b’. Here, this is not the case.

Observed

Expected

(O-E)^2

(O-E)^2/E= chi square value

W_V_

30

20.75

85.5625

4.12349398

W_vv

10

20.75

115.563

5.56927711

wwV_

12

20.75

76.5625

3.68975904

wwvv

31

20.75

105.063

5.06325301

Total

83

18.4457831

Calculated value = 18.44

Degree of freedom = (rows-1) (columns-1) = (4-1)* (4-1) = 9

Tabulated value = taken from chi square table = 16.92

Level of significance (given) = 0.05

Null hypothesis is accepted if calculated value is less than tabulated value.

Here, tabulated value<calculated value, so, null hypothesis should be rejected.

So, the population is not assorting independently according to Mendelian ratio of 9:3:3:1 (part c). Chi-square test does not support the hypothesis.

Alternate hypothesis should be accepted.

	Observed	Expected	(O-E)^2	(O-E)^2/E= chi square value
W_V_	30	20.75	85.5625	4.12349398
W_vv	10	20.75	115.563	5.56927711
wwV_	12	20.75	76.5625	3.68975904
wwvv	31	20.75	105.063	5.06325301
Total	83			18.4457831