Question

Which of the following methods would best be applied to determine if the observed phenotypic ratios of a two-factor cross fit the expected ratios by Mendelian inheritance?

-Chi square test
-Product rule
-Binomial expansion equation
-Sum rule

Answer 1

The Chi square test is the best method to compare observed phenotypic ratios to those expected by Mendelian inheritance in a two-factor cross.

Step-by-step explanation:

To determine if observed phenotypic ratios fit the expected ratios by Mendelian inheritance, the best method to apply would be the Chi square test. This statistical test compares the observed frequencies of phenotypes against the expected frequencies, which are calculated based on Mendelian genetic principles, such as the 9:3:3:1 ratio for a two-factor cross if genes are independently assorting.

The Chi square test is particularly useful because it considers the probability of the observed variation due to chance alone. When the p-value from the test is high, it indicates that the observed variation could indeed be due to chance, therefore supporting a Mendelian pattern of inheritance. However, if the p-value is low, then the observed variation is less likely due to chance, and there might be other factors affecting the inheritance pattern.

Specifically, for a dihybrid cross (such as the AaBb x AaBb example), you would expect the offspring to manifest in the proportions 9:3:3:1. The Chi square test calculates how well the actual data fits this expected ratio, thereby providing a statistical measure of the goodness of fit.