Exercise 9: Microevolution The Hardy-Weinberg Equilibrium
when you perform your chi-square analysis, consider these important reminders: The criterion for accepting or rejecting the null hypothesis is
a p value that is greater then 0.05. if the p value is greater than 0.05, the null hypothesis is accepted, meaning evolution did not occur. if the p value is less than 0.05, the null hypothesis is rejected, meaning evolution occurred
what is a chi-square?
a statistical test that is used to determine whether the observed data is close enough to the data expected by a hypothesis to be acceptable
why would we use a chi-square analysis of observed allele frequency?
chi-square tells you how many times out of 100 a deviation from the expected results is due to chance alone
The Hardy-Weinberg Equilibrium (easy definition)
condition that occurs when the frequency of alleles in a particular gene pool remain constant over time
when you perform your chi-square analysis, consider these important reminders: Degrees of freedom are
equal to the number of groups minus 1. (for example, in a population with two alleles for color, B is blue and b is white, the degree of freedom is 1)
If allele frequency does NOT change from one generation to the next, then
evolution did not occur
If allele frequency DOES change from one generation to the next, then
evolution occured
if the null hypothesis is rejected, then
evolution occurred
The Hardy-Weinberg equilibrium is an important standard to
monitor changes of allele frequency in a population
The Hardy-Weinberg Equilibrium (hard definition)
serves as a null hypothesis for evolution; in other words, if the allele frequencies of a population do not adhere to Hardy-Weinberg equilibrium, then evolution has occured
The Hardy-Weinberg model allows us to compare
the OBSERVED allele frequency over time to the allele frequency we would EXPECT if the population was not evolving (i.e. the Hardy-Weinberg equilibrium)
The Hardy-Weinberg equilibrium states that
the allele frequency and genotype frequency of a population will remain the same and no evolution will occur over successive generations if five basic assumptions are met
what are the five basic assumptions that need to be met in the Hardy-Weinberg equilibrium?
the population is large, mutations do not occur, migration does not occur, mating is completely random, and selection does not occur (i.e. all genotypes have equal reproductive success)
If we can say that chance has caused the difference between the observed and expected results, then
we can say that our results support the null hypothesis (i.e. evolution did not occur)
how do we determine if the difference between the observed and expected allele frequencies in the population of offspring is due to chance alone or some other causes?
we can use a chi-square analysis of observed allele frequency
when you perform your chi-square analysis, consider these important reminders: The probability value (or p value) is associated with
your chi-square and degrees of freedom and represents the percent likelihood that the deviation from the expected results is due to chance alone
