Question

4. Use Chi-square to test which of 2 possible ratios is the most probable ratio of progeny kernels. Use this information to determine the cross type and parental genotype. Show your work here or on a separate sheet to receive full credit. Cross type does not refer to the type of epistasis! Colored aleurone Colorless aleurone Ear code Ratios tested Degrees of freedom Chi- square value Accept or reject Cross type purple red yellow white A 668 479 Parental genotype(s) for ear A .X (5 pts)

can you please explain how to determine which 2 ratios to select to test? also how do you determine the cross type from this info when the question doesn't as, for the type of epistasis?

Answer 1

ANSWER :-

Taking the above mentioned data into consideration, we can state that there are two characters in consideration out of which one should be dominant and the other should be recessive and taking into consideration the laws of inheritance, the ratio is stated to be 3:1 taking into consideration epistasis is not functional. Another ratio that is expected is 9:7 due to the phenomena of complementary gene.

Null Hypothesis :- There is no statistically significant relationship between the ratios (3:1/9:7) and the given data.

Lets make the chi-square test :-

	Observed	Expected	(O-E)2/E
Red (coloured aleurone)	668	860.25 (1147x3/4)	42.96
Yellow (colourless aleurone)	479	286.75 (1147x1/4)	128.89
	1147		171.85

The level of significance is stated to be (0.05) and the degree of freedom is (2-1 = 1) and hence the p-value can be found out to be 0.0000000001 and as this value is less than 0.05, the null hypothesis is rejected indicating that there is an association between the 3:1 ratio and the provided data.

Lets make the second chi-square test :-

	Obsserved	Expected	(O-E)2/E
Red (coloured aleurone)	668	645.1875	0.80
Yellow (colourless aleurone)	479	501.8125	1.03
	1147		1.83

The p-value is found out to be 0.1761 which is more than the value of 0.05 at 5% level of significance and 1 degree of freedom. This indicates that the null hypothesis should be rejected.

So, the cross should be a monohybrid cross leading to a ratio of 3:1. Lets consider the character is being encoded by gene 'A' and hence the parental genotype would be homozygous dominant/recessive (AA/aa) and the F1 progeny will be heterozygous (Aa) which will be considered as the parents to undergo self-cross to give the ratio of 3:1.

	A	a
A	AA	Aa
a	Aa	aa