Question

2) Consider a hairy pea plant that was grown from yellow seed (an F1 hybrid). This hybrid had one parent (P1) that was an inbred variety with no hairs and was grown from a green seed. P2 was also an inbred variety, but grown from a yellow seed and had hairy leaves.

After a backcross of the F1 hybrid to the P1 parent the following progeny are observed.

Yellow seed/Smooth               29

Yellow seed /Hairy                 82

Green seed /Smooth                9

Green seed /Hairy                   30

a) What is the null hypothesis for the ratio of progenies based on the backcross described above.

b) Using a Chi square statistical test, do you reject or fail to reject the null hypothesis. Show your calculations.

c)Is there an easy explanation for your conclusion?

Answer 1

a) Null hypothesis: The observed values are not deviating from expected mendilian dihybrid test cross ratio i.e. 1:1:1:1.

b) Test static- Chisqaure test

Category	Yellow seed /Hairy	Yellow seed/Smooth	Green seed /Hairy	Green seed /Smooth	Total
Observed values (O)	82	29	30	9	150
Exptected Ratio (ER)	1	1	1	1	4
Exprected Values (E)	37.5	37.5	37.5	37.5
Deviation (O-E)	44.5	-8.5	-7.5	-28.5
D^2	1980.25	72.25	56.25	812.25
D^2/E	52.80667	1.926667	1.5	21.66	77.89333
X^2	77.89333
Degrees of freedom	4	-	1	3

Inference: The calculated chi square value i.e. 77.89 is greater than the table value i.e. 7.82 at 3 DF and 0.05 probability. Hence the null hypothesis is rejected.

c)Is there an easy explanation for your conclusion?

The calculated chi square value i.e. 77.89 is greater than the table value i.e. 7.82 at 3 DF and 0.05 probability. Hence the null hypothesis is rejected. Which means the genes are linked genes (present on the same chromosome)