Genetics - Exam Ii Prep

Front 1

What are the 2 assumptions for the Hardy-Weinberg Law?

Back 1

1) Constant allele frequencies over time

2) predictable genotype frequencies

Front 2

Under H-W, a 2 allele system will have the predictable frequencies of:

Back 2

p^2, 2pq, q^2

Front 3

At H-W equilibrium...

Back 3

...NO evolution occurs.

It meets the 2 assumptions for H-W:
1) Constant allele frequencies over time

2) predictable genotype frequencies

Front 4

In the H-W model, the variables:

p and q

...represent which alleles?

Back 4

p = f(A) = the dominant allele

q = f(a) = the recessive allele

Front 5

H-W Model:

Frequency of heterozygotes in a randomly mating population is...

Back 5

...2pq

Front 6

What are 3 important points to remember about the H-W model in terms of allele frequencies?

Back 6

1) Allele frequencies exactly determine genotypic freq. in the next generation.

2) Allele freq. in the new generation (p' and q') are identical to those now (p and q)

3) With random mating, allele freq. will always be p and q, and genotype freq. will always be:
p^2, 2pq, and q^2.

Front 7

H-W:

Assuming random mating, the genotypic frequencies will always be:

Back 7

p^2

2pq

q^2

Front 8

H-W:

Define the variable:

H_o

Back 8

Observed frequency of heterozygotes in the sample

Front 9

H-W:

Define the variable:

H_E

Back 9

Expected freq. of heterozygotes in sample.

Front 10

H-W:

Define the variable:

q^2

Back 10

The genotypic frequency for homozygous recessives in a randomly mating population.

Front 11

H-W:

Define the variable:

p^2

Back 11

The genotypic frequency for homozygous dominant in a randomly mating population

Front 12

H-W:

Define the variable:

q

Back 12

The frequency of individuals that carry the recessive allele.

Front 13

H-W:

Define the variable:

p

Back 13

The frequency of individuals that carry the dominant allele

Front 14

If we assume H-W freq., what kind of test can we NOT do?

Why?

Back 14

We cannot do a X^2 (chi-square) test.

We can only do the test when the number of heterozygotes (H_o) is *actually known*.

For entire populations, this is difficult.

Front 15

The 5 assumptions for HW equilibrium are:

Back 15

a - Random mating

b - Large population size (no genetic drift)

c - No mutation

d - No migration

e - No natural selection (no genotype is more pervasive than another)

Front 16

H-W:

Define the variable:

2pq

Back 16

The expected frequency of heterozygous individuals, if mating were random.

Front 17

Define:

Inbreeding Coefficient of an Individual

Back 17

F_I

The probability that the individual carries alleles that are identical by descent.

Front 18

Non-random mating occurs when mate choice is influenced by:

(2 factors)

Back 18

1 - Phenotype

2 - Genetic relatedness

Front 19

Non-Random mating:

What are the two types of mating based upon Phenotype?

Back 19

1) Positive assortative mating

2) Negative assortative mating

Front 20

Define:

Positive Assortative Mating

Back 20

Mating with the same phenotype more often than if chosen randomly.

Front 21

Define:

Negative Assortative Mating

Back 21

Mating with the same phenotype less often than if chosen randomly.

(opposites attract)

Front 22

Non-Random mating:

What are the two types of mating based upon Genotype?

Back 22

1) Inbreeding

2) Outbreeding

Front 23

Define:

Inbreeding

Back 23

Mating with relatives more often than if chosen randomly.

Front 24

Define:

Outbreeding

Back 24

Mating with relative less often than if chosen randomly.

Front 25

Non-random vs. H-W:

In Positive Assortative Mating there are more _____ and fewer _____ than under H-W.

Back 25

...homozygous...

...heterozygous...

Front 26

Non-random vs. H-W:

Both negative assortative mating and outbreeding lead to fewer _____ and more _____ than under H-W.

Back 26

...homozygous...

...heterozygous...

Front 27

Non-Random mating:

Name and define the variable:

F

Back 27

Inbreeding coefficient

The probability (frequency) that two gene copies in an individual are identical by descent.

Front 28

Define:

The concept of Identity by Descent

Back 28

Quantifies the probability that 2 gene copies derive from the same parental chromosome from a past generation.

Front 29

Pedigrees that begin with a half-sibling mating have what type of pathway?

Back 29

1-loop pathway

Front 30

Pedigrees that begin with a full-sibling mating have what type of pathway?

Back 30

2-loop pathway

Front 31

Define:

Autozygosity

Back 31

Two alleles that are identical by descent.

Front 32

Define:

Allozygosity

Back 32

Two alleles that are NOT identical by descent.

Front 33

Gene flow alters frequencies _____ populations.

Back 33

...within...

Front 34

Gene flow _____ genetic difference among populations.

Back 34

...reduces...

Front 35

Gene flow is also called:

Back 35

The great homogenizer

Front 36

Gene flow _____ speciation.

Back 36

...retards...

Front 37

Speciation requires...

(i.e. it requires "this" before it can occur)

Back 37

...genetic divergence.

Front 38

The homogenizing effects of gene flow can be eliminated by...

Back 38

...geographic isolation.

Front 39

What are 3 reasons why gamete production and fertilization are subject to random sampling error.

Back 39

1 - The number of parents is not infinite.

2 - The number of gametes per parent is not infinite.

3 - The number of zygotes in next generation is not infinite.

Front 40

Sampling error of gametes results in...

Back 40

...random changes in allele frequency over time.

Front 41

3 major results of Genetic Drift.

Back 41

1 - Changes due to genetic drift are random and can't be accurately predicted.

2 - Drift causes allele frequencies within a population to change over time.

3 - Drift causes populations to diverge genetically over time.

Front 42

Explain how genetic drift "erodes" genetic variation over time.

Back 42

- Some rare alleles are lost.

- Alleles eventually become fixed (q = 1) or lost (q = 0) in all populations of finite size.

Front 43

Genetic Drift:

If an alleles frequency has become "fixed" then:

q = ?

Back 43

q = 1

i.e. that is found in all individuals of the population.

Front 44

Genetic Drift:

If an alleles frequency has become "lost" then:

q = ?

Back 44

q = 0

i.e. that allele is not found in the population any more.

Front 45

How is the magnitude of the sampling error and the number of trials related to one another?

What does this mean?

Back 45

The magnitude of the sampling error is inversely related to the number of trials (2N).

This means as your number of trials gets larger, your sampling error will go down.

Front 46

What is the equation for:

The probability of a new allele arising by mutation becoming fixed by genetic drift?

What does this equation say?

Back 46

P(fixation) = 1/2N

That as N (your sample size) becomes larger, the probability that this allele will become fixed (i.e. the allele will be present in all individuals) goes down.

Front 47

What is the equation for:

The probability of a new allele arising by mutation becoming lost by genetic drift?

What does this equation say?

Back 47

P(loss) = 1 - (1/2N)

That as N (your sample size) becomes larger, the probability that this allele will become lost (i.e. it won't exist in any individuals of the population) goes up.

Front 48

The Founder Effect:

What are 'founders'?

What does the Founder Effect result in?

Back 48

Founders are only a sample of the source population.

Results in:
1 - Different allele frequencies in founder population

2 - Lower variation in founder population.

Front 49

What are 2 special cases of Genetic Drift?

Back 49

1 - The Bottleneck Effect

2 - The Founder Effect.

Front 50

What is the Bottleneck Effect?

What does it result in? (2 things)

Back 50

A population undergoes a drastic reduction in population size (N).
The organisms after this decrease are the sample population.

Bottleneck Effect results in:
- Changes in allele frequency.
- Loss of genetic variation.

Front 51

What are 2 ways to restore lost variation from the bottleneck effect?

Back 51

1 - Gene flow from other populations.

2 - Mutation (a very *slow* process)

Front 52

What is another phrase for "Random Sampling Error of gametes"?

Back 52

Genetic Drift

Front 53

Reproduction in populations is a _____ event.

Back 53

...probabilistic...

Front 54

Define:

Genetic Drift

Back 54

The random sampling error of gametes resulting in fluctuations in allelic frequencies from one generation to the next.

Front 55

Define:

Adaptation

Back 55

The progressive genetic "improvement" of populations by natural selection.

Front 56

What are the 4 general points about natural selection?

Back 56

1 - Natural Selection is an important evolutionary force, but not the only one. (many alleles are selectively "neutral").

2 - Natural Selection operates on phenotypes.

3 - Gene pools respond to Natural Selection if phenotypic differences have a genetic basis.

4 - Selection operates to better adapt populations to their environment.

Front 57

Define:

Natural Selection

Back 57

The differential reproduction and survival of genetically determined forms.

Front 58

How does Natural Selection better adapt populations to their environment?

Back 58

Natural Selection increases the frequency of adaptive genotypes.

Front 59

Define:

Fitness

Back 59

The capacity to survive and reproduce, based on phenotypic differences among individuals.

*or*

Reproductive contribution of a genotype to future generations.

Front 60

Define:

Absolute Fitness

Back 60

(population genetics)

The average contribution of all individuals *with a particular genotype* to future gene pools

EXA:
Avg % survival (x) avg. # offspring

Front 61

Define:

Relative fitness

Back 61

(population genetics)
Variable = w

(Absolute fitness) / (Absolute fitness of best genotype)

*The best genotype has (w = 1)

Front 62

Define:

Selection coefficient (s)

What does it equal?

Back 62

Measures the intensity of selection on a genotype.

s = 1 - w

*w = relative fitness

Front 63

What are the 3 components of fitness?

Back 63

1 - Viability (zygotic) selection

2 - Sexual selection

3 - Fertility selection

Front 64

If there is *no* gene flow in a population, genetic drift will lead to...

Back 64

...maximal population divergence

i.e. alleles will eventually become fixed or lost.