In guinea pigs, white coat (w) is recessive to black coat (W) and wavy hair (v)
ID: 309799 • Letter: I
Question
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.Explanation / Answer
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