Ch. 27 and 28: Evolutionary Processes and Probability Statistics

Question 1

What is genetic drift?

Answer 1

The random increase or decrease (basically any change) in allele frequency due to chance in a population

Question 2

What is the relationship between population bottleneck and genetic bottleneck?

Answer 2

Occurs when a population experiences a sudden sharp reduction in population size
–Causes genetic drift resulting in a uniform fixation of alleles

Question 3

What is the founder effect?

Answer 3

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)

Question 4

What causes the founder effect?

Answer 4

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

Question 5

What is gene flow?

Answer 5

The flow of alleles from one population to another through the physical movement of individuals (migration)

Question 6

What is the effect of gene flow?

Answer 6

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

Question 7

In what kind of population is genetic drift most pronounced?

Answer 7

Drift is greatest in small populations

Question 8

What is sexual selection?

Answer 8

A mode of natural selection where some individuals out-reproduce others of a population because they are better at securing mates

Question 9

What is the ultimate source of genetic variability and why?

Answer 9

Mutation, because it is the only thing that can create genetic diversity

Question 10

What is allele fixation?

Answer 10

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

Question 11

What type of data should a chi square test normally be applied?

Answer 11

Categorical data (there are a few exceptions to this rule)

Question 12

What is a chi-square test?

Answer 12

The chi-square test statistic can be thought of as a relative measure of departure of observed results from theoretical predictions

Question 13

What is the equation to calculate chi-square?

Answer 13

Chi-square=
sum (Oi-Ei)^2/Ei
–Where Oi is the observed number of outcomes and Ei is the expected number of outcomes

Question 14

What do degrees of freedom correspond to in a problem?

Answer 14

The number of independent variables

Question 15

How do you calculate the DOF for a chi-square test?

Answer 15

DOF=n-1,

where n=# of categories in the problem

Question 16

What determines the threshold (the critical value) between acceptance and rejection of a hypothesis ?

Answer 16

The degrees of freedom

• -The more DOF, the greater the critical value
• -p is found by a p table once DOF is calculated

Question 17

What is another name for a p-value?

Answer 17

Alpha

Question 18

How do you reject the null hypothesis?

Answer 18

If your test statistic is less than the critical value (p value or alpha) you can reject the null hypothesis

Question 19

How would you analyze the rolling of a die with a chi-square test?

Answer 19

–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

Question 20

What does a p < 0.05 indicate relative to the null hypothesis?

Answer 20

• -That the null hypothesis is rejected
• -An external influence caused a significant change
• -Relationship didn’t occur by chance

Question 21

What does a p > 0.05 indicate relative to the null hypothesis?

Answer 21

• -Fail to reject the null hypothesis (accepted)
• -An external influence did not cause a significant change
• -Results occurred within normal deviation

Question 22

What is a p value?

Answer 22

The probability of an event occurring

Question 23

What does a smaller p value represent?

Answer 23

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)

Question 24

Why is the chi-square test useful?

Answer 24

Allows one to estimate the probability that real categorical data are nonrandom (ordered by some outside influence)

Question 25

Do most of the evolutionary mechanisms lead to an increase or a decrease in genetic diversity?

Answer 25

A decrease (remember selection will favor certain traits over others)

Question 26

What is the source of increasing genetic diversity?

Answer 26

Mutation

Question 27

Does genetic drift tend to increase or decrease genetic diversity over time?

Answer 27

Decreases it

Question 28

Why is inbreeding not considered an evolutionary process?

Answer 28

It will not result in a change in allele frequency over time

–However, it usually decreases the mean fitness of a population

Question 29

What is a major consequence of gene flow in natural populations?

Answer 29

It tends to homogenize the populations between which migration is occuring

Question 30

How do you calculate a chi^2 test statistic when given observed results and a genotypic ratio?

Answer 30

–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