Question

It has been proposed that the presence of black markings on the throat of kung fu geckos is coded by a dominant allele (B) and that the absence of such markings is coded by a recessive allele (b). To test this idea, heterozygous individuals are crossed (Bb x Bb) producing 500 offspring of which 350 have black markings and 150 don’t have black markings. Based on a punnett square, the expected phenotypic ratio for black markings to no black markings is 3:1.
Required:
Write down the correct statistical approach to test if the data is consistent with the expected 3:1 ratio.

Answer 1

Answer:

See the answer below

Explanation:

The correct statistical approach to test if the data is consistent with the expected 3:1 ratio would be the Chi square.

Chi-square = $\frac{(O - E)^2}{E}$ where O = observed frequency and E = Expected frequency. In this case:

     Phenotype                 O                   E                          Chi square

• Blacks                       350      3/4 x 500 = 375             $\frac{(350-375)^2}{375}$ = 1.67

• Non blacks                150       1/4 x 500 = 125             $\frac{(150-125)^2}{125}$ = 5

Total Chi square = 1.67 + 5 = 6.67

Degree of freedom = 1

Tabulated Chi square = 3.841

Since the calculated Chi-square is more than the tabulated value, the null hypothesis is rejected and we conclude that the data is not consistent with the expected 3:1 ratio.