Chapter 7

Question 0

What are three criticisms of Mendel’s conclusions?

Answer 0

• seemed to be opposed to most biological observations
• unclear as to whether his observations were consistent with Darwin’s theory
• trait frequencies as observed in nature were not consistent with frequencies expected under Mendelian inheritance

Question 1

Why won’t alleles disappear?

Answer 1

Heterozygotes can “hide” the recessiveness

Question 2

What did GH Hardy do? (4)

Answer 2

• developed model to predict the population level consequences of Mendelian inheritance
• Showed Punnett was correct
• demonstrated that dominant alleles would not replace recessive alleles over time
• The frequency of an allele neither decreases or increases simply because its recessive or dominant

Question 3

Population genetics

Answer 3

=> provides math description & modilizes evolution process

-Investigates how the genotype frequencies in an offspring population are related to the genotype frequencies in a parental population.

Question 4

Individual versus Population level thinking

Answer 4

Individual thinking: what gametes and offspring are produced, in what frequencies, from a given pair of parents?

Population thinking: how do the characteristics of the population change over time as the result of evolutionary processes?

Question 5

Qualitative prediction

Answer 5

If a trait is beneficial we would expect to see its frequency in the population increase

Question 6

Quantitative prediction

Answer 6

Numerical predictions about evolutionary dynamics

Question 7

Stasis

Answer 7

When genotype frequencies (AA/Aa/aa) or allele frequencies (A or a) stay the same

Question 8

Steady state frequencies

Answer 8

equilibria of our models

Question 9

When is a system in equilibrium?

Answer 9

When the system has reached a state where it does not change in the absence of outside forces or processes acting on it

Question 10

Stable equilibrium conditions (2)

Answer 10

• at this point the system DOES NOT CHANGE
• If perturbed by small amount the system will return to this point

*upside down cup with ball on the bottom

Question 11

Unstable equilibrium conditions (2)

Answer 11

At this point the system DOES NOT change

If perturbed or displaced by some small amount, the
system will move further away from its initial position at rest.

Question 12

Neutral equilibrium conditions (2)

Answer 12

At this point, system does not change

If perturbed by small amount the system will stay in its displaced position, rather than returning to the original position as it would in a stable equilibrium, or moving further away as it would in an unstable equilibrium.

Question 13

Mixed equilibrium conditions (2)

Answer 13

At this point the system does not change

If perturbed to the left or the right, the system will return to its starting point. If perturbed forward or backward, the system will stay in the new displaced position

Question 14

What does the Hardy Weinberg model serve as & what does it tell us about genotype frequencies?

Answer 14

A null hypothesis for population genetics [opposite]

Tells us what happens to genotype frequencies when natural selection and other important drivers of evolutionary change are NOT happening

Question 15

What are the three conclusions if there is an absence of evolutionary processes acting on alleles?

Answer 15

• Frequencies of A1 and A2 do not change over time
• With allele frequencies and random mating it is possible to predict the equilibrium genotype frequencies
• All alleles no matter their initial frequencies will reach Hardy-Weinberg equilibrium in a single generation

Question 16

First and Second Hardy Weinberg assumptions?

Answer 16

• Natural selection is not operating on the trait or traits affected by the locus in question => no natural selection
• Individuals have no preference for others with similar (or dissimilar) genotypes => random mating

Question 17

Third, fourth, and fifth HW assumptions:

Answer 17

• No mutation is occurring
• There is no migration into or out of the population => no new alleles
• Population is infinite in size => no genetic drift

Question 18

What are the 3 possible genotypes of A1 and A2? Sum of genotype frequencies?

Answer 18

A1A1, A1A2, A2,A2 = 1

Question 19

What equilibrium does p2, 2pq, and q2 represent, given allele frequencies p and q?

Answer 19

Stable equilibrium

Question 20

What type of equilibrium are the allele frequencies p and q?

Answer 20

Neutral

Question 21

What frequency should be reached by heterozygous frequency at HW equilibrium?

Answer 21

f[A1A2] = 0.5

Question 22

What is the basic procedure of the HW Model?

Answer 22

1. Experimentally collect frequency of alleles in population
2. Determine genotype frequencies
3. Use genotype frequencies to calculate the actual allele frequencies in population
4. Calculate the expected HW
5. Use chi square test to compare expected to observed for significance

Question 23

What is the whole idea of HW model, and an example?

Answer 23

To be able to tweak an assumption and see their affect.

If mutation is introduced and it fluctuates your data, then you know that’s driving your population

Question 24

Selection coeffiecient

Answer 24

Describes the fitness reduction of the light phenotype relative to dark phenotype.

Question 25

How is fitness set up in light and dark phenotypes? What does it mean is s=0 or 0.25?

Answer 25

Fitness of dark type is set to 1 Fitness of light type set to 1-s If s=0; no selection against alllele If s=0.25; 25% reduction in fitness

Question 26

Frequency-independent selection & example

Answer 26

Fitness associated with a trait is not directly dependent on the frequency of the trait in a population Example: pocket mice

Question 27

Directional selection

Answer 27

One allele is consistently favored over the other allele; takes long because it's being masked

Question 28

What if A1 is codominant or dominant to A2?

Answer 28

heterozygotes have selection advantage

Question 29

What if A1 is recessive to A2?

Answer 29

Heterozygotes have same fitness as A2A2 homozygotes

Question 30

Codominant

Answer 30

equal expression

Question 31

Overdominance

Answer 31

heterozygotes has highest fitness

Question 32

Balanced polymorphism

Answer 32

-A stable equilibrium that's polymorphic; allele frequencies will return to their equilibrium values after a perturbation away from equilibrium

Question 33

Balancing selection, and example

Answer 33

selection that leads to balanced polymorphism * generally rare * classic example is sickle cell anemia

Question 34

Underdominance

Answer 34

Heterozygote has lower fitness than homozygotes

Question 35

Overdominance and underdominance are very rare, why?

Answer 35

If the allele goes above critical threshold frequency, it goes to fixation If the allele goes below this frequency, it's lost from the population

Question 36

Why are overdominance and underdominance classified as frequency independent selection?

Answer 36

Fitness of each genotype, and its corresponding phenotype, is constant and independent of the frequencies of genotypes in the population

Question 37

Frequency-Dependent selection

Answer 37

Occurs when the costs and benefits associated with a trait depend on its frequency in the population

Question 38

What is POSITIVE frequency dependent selection? What happens when phenotype is favored and controlled by two alleles at a single locus?

Answer 38

Fitness associated with trait that INCREASES as the frequency of the trait increases in population - Each phenotype favored once becomes sufficiently common in the population. - If phenotype controlled at a single locus, one of the two alleles will become fixed and the other will be lost

Question 39

What is NEGATIVE frequency dependent selection? When are phenotypes favored and controlled by two alleles at a single locus?

Answer 39

Fitness associated with trait DECREASED as the frequency of the trait increases in population. - Each phenotype favored when rare - If phenotype controlled by two alleles at a single locus, both will be maintained in a balanced polymorphism (form of balancing selection)

Question 40

Example of positive frequency-dependent selection

Answer 40

Flat nail species; The higher the frequency of either coil direction in the population the higher their fitness

Question 41

Example of Negative frequency-dependent selection

Answer 41

Scale-eating cichlid fish (two morphs: right and left handed mouth openings); As one mouth opening became dominant, its prey became aware of protecting that side decreasing the fitness of the most common mouth morphology = maintaining it ~50%

Question 42

Viability selection

Answer 42

Fitness differences that arise because of differences in rates of survival and mortality

Question 43

Fecundity selection

Answer 43

Natural selection operating on the number of offspring produced

Question 44

Semelparous species

Answer 44

Organisms that reproduce once at the end of their lives

Question 45

Mutation; two facts?

Answer 45

Ultimate source of variation Can change allele frequencies in a population

Question 46

Which acts slower, mutation or selection?

Answer 46

Mutation operate acts slower than selection.

Question 47

How does mutation affect genotype frequencies?

Answer 47

If other HW assumptions are met, the genotype frequencies will always be in standard HW proportions

Question 48

Even if A1 gets favored, why won't it ever get fixed? What will be reached?

Answer 48

A1 although favored will never be fixed because A2 alleles are constantly being generated by mutation. => equilibrium will eventually be reached.

Question 49

Mutation selection balance

Answer 49

Equilibrium state where the action of natural selection to DECREASE the frequency of A2 is exactly balanced by the action of mutation to produce new A2 alleles by mutation from A1

Question 50

Since several human diseases negatively affect fitness, why haven't they been eliminated from population?

Answer 50

Mutation-selection balance