Ch. 27 and 28: Evolutionary Processes and Probability Statistics Flashcards
What is genetic drift?
The random increase or decrease (basically any change) in allele frequency due to chance in a population
What is the relationship between population bottleneck and genetic bottleneck?
Occurs when a population experiences a sudden sharp reduction in population size
–Causes genetic drift resulting in a uniform fixation of alleles
What is the founder effect?
The loss of genetic variation that occurs when a new population is established by a very small number of individuals (their allele frequencies are almost guaranteed to be different from the source population)
What causes the founder effect?
When a founding population (bringing only the alleles they possess) migrates to a new area, genetic drift has a greater influence (natural selection having a much lesser influence), resulting in random fixation of alleles.
–May cause the newer population to be less competitive for resources
What is gene flow?
The flow of alleles from one population to another through the physical movement of individuals (migration)
What is the effect of gene flow?
Gene flow can introduce either high-fitness or low-fitness alleles into less fit or more fit populations respectively. Either way, selection will likely eliminate low-fitness alleles, causing high-fitness alleles to increase in frequency
In what kind of population is genetic drift most pronounced?
Drift is greatest in small populations
What is sexual selection?
A mode of natural selection where some individuals out-reproduce others of a population because they are better at securing mates
What is the ultimate source of genetic variability and why?
Mutation, because it is the only thing that can create genetic diversity
What is allele fixation?
An allele becomes fixed in a population when it reaches a frequency of 100%, i.e.,when every individual in the population has only this allele
What type of data should a chi square test normally be applied?
Categorical data (there are a few exceptions to this rule)
What is a chi-square test?
The chi-square test statistic can be thought of as a relative measure of departure of observed results from theoretical predictions
What is the equation to calculate chi-square?
Chi-square=
sum (Oi-Ei)^2/Ei
–Where Oi is the observed number of outcomes and Ei is the expected number of outcomes
What do degrees of freedom correspond to in a problem?
The number of independent variables
How do you calculate the DOF for a chi-square test?
DOF=n-1,
where n=# of categories in the problem
What determines the threshold (the critical value) between acceptance and rejection of a hypothesis ?
The degrees of freedom
- -The more DOF, the greater the critical value
- -p is found by a p table once DOF is calculated
What is another name for a p-value?
Alpha
How do you reject the null hypothesis?
If your test statistic is less than the critical value (p value or alpha) you can reject the null hypothesis
How would you analyze the rolling of a die with a chi-square test?
–6 categories (possibilities)
–DOF=6-1=5
p=11.07 for 95% confidence level,
–Calculate chi-square from test data and compare to p-value
What does a p < 0.05 indicate relative to the null hypothesis?
- -That the null hypothesis is rejected
- -An external influence caused a significant change
- -Relationship didn’t occur by chance
What does a p > 0.05 indicate relative to the null hypothesis?
- -Fail to reject the null hypothesis (accepted)
- -An external influence did not cause a significant change
- -Results occurred within normal deviation
What is a p value?
The probability of an event occurring
What does a smaller p value represent?
The smaller the p-value the more likely the relationship (ex. as p gets smaller and smaller, away from 0.05, the probability that the change was caused by an outside influence gets greater)
Why is the chi-square test useful?
Allows one to estimate the probability that real categorical data are nonrandom (ordered by some outside influence)
Do most of the evolutionary mechanisms lead to an increase or a decrease in genetic diversity?
A decrease (remember selection will favor certain traits over others)
What is the source of increasing genetic diversity?
Mutation
Does genetic drift tend to increase or decrease genetic diversity over time?
Decreases it
Why is inbreeding not considered an evolutionary process?
It will not result in a change in allele frequency over time
–However, it usually decreases the mean fitness of a population
What is a major consequence of gene flow in natural populations?
It tends to homogenize the populations between which migration is occuring
How do you calculate a chi^2 test statistic when given observed results and a genotypic ratio?
–Add up all observed occurrences (ex. 127 white + 27 red +7 yellow=160 total)
–Add up each value in the ratio (ex. if you have 12:3:1, the total would be 16)
–Calculate Expected Occurences as shown:
16012/16, 1603/16, 160*1/16
–Calculate Chi^2 with data
