1 Monohybrid crosses of two heterozygous pea plants for tall

1. Monohybrid crosses of two heterozygous pea plants for tall height (Tt), resulting in 7582 tall plants and 2543 dwarf plants. Which of the following chi square values is correct? (Hint: remember to first determine the total number of plants produced by the crossing).

A. 0.096 B. 0.062 C. 0.073 D. 1.211

Solution

C). 0.073

Assume that the gene coding for tall plants is T and the gene coding for dwarf plants is, t; T is dominant over t.

Cross between two heterozygotes will have the progeny with the following genotypes:

Tt* Tt --à T_ (3/4, Tall), tt (1/4, dwarf)

Total number of plants is = 10125

The expected proportion of tall plants in the population is = ¾* 10125 = 7593.75

The expected proportion of dwarf plants in the population is = 1/4* 10125 = 2531.25

The chi-squared value is,

CHI - SQUARE (X²):

X² = (O - E)² / E

Where O = Observed frequency

E = Expected frequency

Genotype

O

E

(O-E)

(O-E)^2

(O-E)^2/E

T_

7582

7593.75

-11.75

138.0625

0.018181

tt

2543

2531.25

11.75

138.0625

0.054543

10125

10125

0

276.125

0.072724

Thus, the calculated Chi-square value is 0.0727, or approximately equal to 0.073