In a certain species of flowering plant, the purple allele P is dominant to the Yellow allele p.

A student performed a cross between a purple-flowered plant and a
yellow-flowered plant. When planted, the 146 seeds that were produced from the
cross matured into 87 plants with purple flowers and 59 plants with yellow
flowers.

Calculate the chi-square value for the null hypothesis that the purple-flowered
parent was heterozygous for the flower-color gene. Give your answer to the
nearest tenth.

3.4

Explanation:

If the purple flower is heterozygous:

                Pp    x    pp

            Pp   Pp   pp   pp

the expected ratio of purple flower offspring to yellow flower offspring would be 50:50.

Chi square = where O = observed frequency and E = expected frequency.

phenotype            O              E                 Chi square

purple                   87             73                 = 0.67

yellow                   59             73                 = 2.68

Total = 0.67 + 2.68 = 3.35 to the nearest tenth = 3.4

Degree of freedom = 2 - 1 = 1

Critical Chi square value (alpha = 0.05) = 3.84  

SInce the critical Chi square value is greater than the calculated value, the null hypothesis is accepted.