In peas, inheritance of seed shape, plant size, and seed color follow a pattern

Question

In peas, inheritance of seed shape, plant size, and seed color follow a pattern of Mendelian inheritance For seed shape, round peas, R, are dominant to wrinkled peas, r, for plant size, tall plants, T, are dominant to short plants, t; for seed color, yellow seeds, Y, are dominant to green seeds, y. Suppose a heterozygous plant, Rr Tt Yy, is selfed and the phenotype of the resulting offspring is determined. The results of this cross are shown in the table below. Calculate the chi-square value for this experiment. Phenotype round, yellow, and tall round, yellow, and short 115 round, green, and tal round, green, and short 50 wrinkled, yellow, and tall173 wrinkled, yellow, and short 57 wrinkled, green, and tall 53 wrinkled, green, and short 15 Total: Total offspring 424 Number Chi-square value 1004

Explanation / Answer

The chi-square number will be 32.17. The chi-square value is calculated by the formula: X2 = summetion of (observed number - expected numer)2 / expected number.

Here expected ratio according to Mendelian inhertance will be 9: 3: 3: 1

Here observed number for first phenotype is 424 and the expected number is 450 (according to mendelian inheritance ratio). Therfore (O - E)2 / E = (424 - 450)2 / 450 = 1.50

in the same way for second phenotype the observed number is 115 and the expected number is 115 and therefore (O - E)2 / E = 8.16

For third phenotype: (O - E)2 / E = 7.26

obviously for fourth phenotype (O - E)2 / E = 0

For fifth phenotype (O - E)2 / E = 10.69

For sixth phenotype (O - E)2 / E = 3.2

For seventh phenotype (O - E)2 / E = 1.42

Obviously for eighth phenotype (O - E)2 / E = 0

Therefore chi-square value = 1.50 + 8.16 + 7.26 + 0 + 10.69 + 3.2 + 1.42 + 0 = 32.17

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