A dominant gene A governs the production of purple anthocyan

A dominant gene \"A\" governs the production of purple anthocyanin pigment in tomato stems and its recessive allele \"a\" produces green stem. A dominant gene \"HI\" controls the development of hairy stems and its recessive allele \"hl\" produces hairless stems. A dihybrid purple, hairy plant is test crossed and produces: 73 purple, hairy 12 purple, hairless 75 green, hairless 9 green, hairy Is the purple: green ratio among the test cross progeny compatible with the expectation for segregation? Support your answer using Chi-square analysis.

Solution

If these genes are showing mendilian inheritance, the test cross ration shoud be in 1:1:1:1 ratio.

Chisquare analysis

Null hypothesis : The observed values are not deviating from the 1:1:1:1 ratio

Category

purple hairy

purple hairless

green hariless

green hairy

Total

Observed values

73

12

75

9

169

Exptected Ratio

1

1

1

1

4

Exprected Values

42.25

42.25

42.25

42.25

Deviation

30.75

-30.25

32.75

-33.25

D^2

945.5625

915.0625

1072.563

1105.563

D^2/E

22.38018

21.65828

25.38609

26.16716

95.59172

X^2

95.59172

Degrees of freedom

4-1 = 3

Inference: The calculated chi square value is greater than the table value i.e. 7.82 at 3 DF and 0.05 probability. Hence Null hypothesis is rejected. Those genes are not showing mendilian inheritance which means those are not showing indipendent assortment.

Category	purple hairy	purple hairless	green hariless	green hairy	Total
Observed values	73	12	75	9	169
Exptected Ratio	1	1	1	1	4
Exprected Values	42.25	42.25	42.25	42.25
Deviation	30.75	-30.25	32.75	-33.25
D^2	945.5625	915.0625	1072.563	1105.563
D^2/E	22.38018	21.65828	25.38609	26.16716	95.59172
X^2	95.59172
Degrees of freedom	4-1 = 3