Question

In the garden pea the yellow cotyledon is dominant over the green and the thick pod is dominant over the thin pod. When both characters were considered together in self-fertilized dihybrids, the following proportion appeared in the progeny: 100 green, thick pod, 530 yellow, thin pod, 195 yellow, thick pod, 65 green, thin pod. Does this data behave in a 9: 3: 3: 1 ratio?

Answer 1

Answer:

Answer:

Yellow = Y ; Green = y

Thick pod = P ; Thin pod = p

YyPp x YyPp ----Parents (Self fertilization of Dihybrid)

Yellow cotyledon, thick pod = 9/16

Yellow cotyledon, thin pod = 3/16

Green cotyledon, thick pod = 3/16

Green cotyledon, thin pod = 1/16

Phenotype	Observed(O)	Expected (E)	O-E	(O-E)2	(O-E)2/E
yellow, thick	195	500.63	-305.625	93406.64	186.58
Yellow, thin	530	166.875	363.125	131859.77	790.17
Green, thick	100	166.875	-66.875	4472.27	26.80
Green, thin	65	55.625	9.375	87.89	1.58
Total	890	890			1005.13

Chi-square value = 1005.13

Degrees of freedom = number of categories - 1

= 4-1 = 3

The chi-square value of 1005.13 is greater than the critical value of 7.81 (3 degrees of freedom at 5% p value). Hence we reject null hypothesis and the data is not fit in 9:3:3:1 ratio