In a plant species, you notice that purple and yellow leaf colors, as well as hairy and smooth stems segregate independently. You cross a plant with purple leaves and hairy stems to a plant with yellow leaves and hairy stems, and generate the progeny indicated below: Class Phenotypes
1 68 yellow leaves, hairy stems
2 66 purple leaves, hairy stems
3 22 purple leaves, smooth stems
4 25 yellow leaves, smooth stems
Total: 181
a) Indicate the most likely genotypes of each parent.
b) What pattern of inheritance could explain the progeny results? Based on your answer, what ratios would be expected for the four classes of progeny?
c) Using the chi-square method, test your ratios and indicate whether you accept them or reject them.

The required answer is given below:

Explanation:

a) Assuming C is the gene for leaf color and S is the gene for the stem type.

then, the genotypes for each parent would be-

Yellow leaves, hairy stem parent: ccSs

Purple leaves, hairy stem parent: CcSs

b) Expected ratios of the progeny as below:

68 yellow leaves, hairy stems: 3/8

66 purple leaves, hairy stems: 3/8

22 purple leaves, smooth stems: 1/8

25 yellow leaves, smooth stems: 1/8

Hence, the ratio is - 3:3:1:1

It might possible that  independently assorting single gene pairs could control traits, and that one of the alleles in each pair is dominant.

c) The general formula for calculating X2:

X2 =  the sum of (O - E)2/E,

(where O = observed number)

(E = expected number)

So,

(68 – 68)2 /68 + (66 – 68)2/68 + (22 – 23)2 /23 + (25 – 23)2/23

= 0.276

X2 = 0.276

The chi-square statistic too small, Hence the hypothesis is acceptable.

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