Question

The allele for the albino condition in corn plants is recessive to the allele for normal pigmentation. A cross between two plants heterozygous at this locus produces 126 normal and 66 albino plants.

a. How many plants are expected in each phenotypic class?

b. Determine the X2 value for these data and the goodness of fit.

c. In general, what would be the consequence for the X2 value if

1 - the discrepancy between the observed and expected numbers had been a smaller-for example, with 136 normal and 56 albino plants?

2 - the sample size had been a smaller-for example, with a total of 156 plants, but with the deviations remaining unchanged at + 18 and -18?

Answer 1

The data suggest that albino condition in corn plants is controlled by a single gene with two alleles, C (Normal) and c (albino) and that C is dominant over c.

A cross between two plants heterozygous at this locus produces 126 normal and 66 albino plants.

a. The crosses are Normal (CC) × albino (cc) → F1 Normal (Cc); F1 × F1 → 3/4 Normal (2 CC: 1 Cc), 1/4 albino (cc).

b. The expected results in the F2 are 131 normal and 61 albino.

x2 value and goodness of fit = (131 − 126)2 /126 + (61 − 66)2 /66 = 0.227, which is not significant at the 5% level.

c. In case of 136 normal and 56 albino plants,  x2 value and goodness of fit = 0.249