LECTURE 12 - Population Genetics

Question 1

study of heredity and variation in a population?

Answer 1

population genetics

Question 2

concerned with heredity in groups of individuals or population

Answer 2

Population Genetics

Question 3

studies the genetic constitution of population

Answer 3

Population Genetics

Question 4

all copies of every type of allele at every locus in all members of population?

Answer 4

gene pool

Question 5

GENOTYPE FREQUENCIES

• definition?
• formula

Answer 5

• relative proportion of a specific genotype for a gene to all genotype for that gene in the population

EX:

f(AA) = (no. of AA individuals) / (total number of individuals)

Question 6

GENE FREQUENCIES
- definition
- formulas (2)?

Answer 6

• relative proportion of an allele of a gene to all alleles of that gene in the population

1.) USING RAW DATA
f(A) = [(2 x no. of AA) + (no. of Aa)] / (2 x total no. of individuals)

f(a) = [(2 x no. of aa) + (no. of Aa)] / (2 x total no. of individuals)

2.) USING GENOTYPIC FREQUENCIES
f(A) = f(AA) + f(Aa) / 2
f(a) = f(aa) + f(Aa) / 2

Question 7

Hardy-Weinberg Equilibrium

• states that?
• criteria (2)?

Answer 7

• all allele and genotype frequencies will remain constant from generation to generation

provided that the ff is working:
1. Mendelian Segregation
2. Recombination of Alleles

Question 8

ASSUMPTIONS of Hardy-Weinberg Equilibrium

Answer 8

1. The population is infinitely large.
2. There is random mating.
3. There is no mutation, selection, migration, and genetic drift.

Question 9

3 IMPORTANT consequences of Hardy-Weinberg Equilibrium

Answer 9

a. Gene and genotypic frequencies remain constant.

b. Absence of genetic change in the population

c. Absence of evolution

Question 10

Hardy-Weinberg Equilibrium

formulas (3) for f(genotype)?

formulas (2) for f(gene)?

Answer 10

f(A) = p
f(a) = q

1.) f(AA) = p^2
2.) f(aa) = q^2
3.) f(Aa) = 2pq

4.) f(A) = p
5.) f(a) = q

wherein p^2 + q^2 + 2pq = 1

and p + q = 1

Question 11

CONDITIONS FOR Hardy-Weinberg Equilibrium

Answer 11

1. No Mutations
   - no new alleles are added
2. Random Mating
   - no preference in mates
3. No Natural Selection
   - all genotype have equal survival and reproduction
4. Extremely Large Population Size
   - avoids genetic drift (for ex decrease of population due to accidents; if unti survivors mapipilitan mag mate with other species)
5. No gene flow
   - no migration in or out of population

Question 12

CASE 1: COMPLETE DOMINANCE

Consider phenylketonuria (PKU), a metabolic disorder that results from homozygosity for a recessive allele and occurs in about one out of every 10,000 babies born in the United States.

What is the frequency of carriers?

Answer 12

f(aa) = 0.0001 (1 out of 10000)

√(q^2) = √(0.0001)

q = 0.01

p = 1-q
p = 1-0.01

p = f(AA) = 0.99

f(Aa) = 2pq = 2(0.99)(0.01) = 0.0198

ANSWER: f(Aa) = 0.0198

Question 13

CASE 2: CODOMINANCE

Codominance
Problem: In cattle, red coat and white coat are codominant traits. In heterozygotes, the two alleles are separately expressed resulting in roan coat. A cattle farm has 400 cattle with 256 having red coat.

What is the frequency of the cattle with white coats? with roan coat?

A - red
a - white
Aa - roan

Answer 13

n = 400
f(red cattle) = 256

f(AA) = p^2 = 256/400 = 0.64

√(p^2) = √(0.64)
p = 0.8

q = 1-p
q=1-0.8
q=0.2

f(aa) = q^2 = (0.2)^2 = 0.04
f(Aa) = 2pq = 2(0.8)(0.2) = 0.32

ANSWER:
f(white coat) = 0.04
f(roan coat) = 0.32

Question 14

CASE 3: SEX-LINKED TRAITS

Colorblindness is an X-linked recessive trait in humans. A recent survey has shown that 1 in 12 males in the US have some degree of color blindness.

What is the estimated frequency of carriers in the US? What is the estimated frequency of normal vision females?

X^A - normal
x^a - colorblindness

Answer 14

f(X^a Y) = q = 1/12 = 0.08

p = 1 - q = 0.92

f(X^A X^a) = 2(0.08)(0.92) = 0.1472

f(normal vision females)
= f(X^A X^A) + f(X^A X^a)
= p^2 + 2pq = 0.9936

Question 15

in sex-linked traits, which of the 2 (male vs female) can be carriers for X-linked traits?

how about for Y-linked?

Answer 15

X-linked = only females

Y-linked = none can be carriers

Question 16

FORMULA FOR THE FREQUENCY OF THE FF:

1. f(X^A X^A)
2. f(X^A X^a)
3. f(X^a X^a)
4. f(X^A Y)
5. f(X^a Y)

Answer 16

1.) p^2
2.) 2pq
3.) q^2

4.) p
5.) q

Question 17

in multiple alleles (blood type), what is the formula for frequency of alleles A, B, and O?

Answer 17

f(A) = p
f(B) = q
f(O) = r

wherein p + q + r = 1

Question 18

FORMULA FOR THE FREQUENCY OF THE FF:

1. f(AA)
2. f(AO)
3. f(BB)
4. f(BO)
5. f(AB)
6. f(OO)

Answer 18

1.) p^2
2.) 2pr
3.) q^2
4.) 2qr
5.) 2pq
6.) r^2

Question 19

FACTORS that disrupt the Hardy Weinberg Equilibrium

• 2 categories of these factors?
• 4 factors in total?

Answer 19

SYSTEMATIC (predictable magnitude and direction)
- mutation
- selection
- migration

DISPERSIVE (predictable magnitude, but unpredictable direction)
- genetic drift

Question 20

composed of individuals in the population that are involved in sexual reproduction

Answer 20

Effective population size

Question 21

direct contributors to the gene pool for the next generation

Answer 21

Effective population size

Question 22

mutation vs selection vs migration

Answer 22

▪ Mutation - transformation of an allele to another allele

▪ Selection – specific genotypes may have less or more survivability and reproductive capability

▪ Migration – alleles can be introduced into a population

Question 23

4 types of mutation

+ notation for first 2

Answer 23

1. Forward mutation: A->a (u)
2. Backward mutation: a ->A (v)
3. Recurrent mutation: occurs repeatedly in a population
4. Nonrecurrent mutation: occurs only once in a population

Question 24

MUTATION - ONE-DIRECTION

formula for p / f(A) for:

1. first gen
2. second gen
3. n gen

Answer 24

1.) p1 = p0 - (u)(p0)

2.) p2 = p1 - (u)(p1)

3.) pn = [p0] [(1-u)^n]

Question 25

MUTATION - TWO-DIRECTION 1. formula for p / f(A) 2. formula for q / f(a) 3. formula for 1st gen p 4. formula for n gen p

Answer 25

p = (v) / (u+v) q = (u) / (u+v) p1 = p0 + (vq0 - up0) pn = pn-1 + (vq0 - up0) **pn-1 = p subscript (n-1)

Question 26

when does bidirectional mutation occur?

Answer 26

when there is constant tug-of-war between u and v

Question 27

what is selection pressure (s)? interpret: s=0

Answer 27

force preventing the survivability and reproductive capability s = 0 ; no disadvantage s = 1 ; lethal

Question 28

3 types of SELECTION in terms of reproductive ability of genotype?

Answer 28

1.Directional – either one of the homozygotes is favored 2.Disruptive – both of the homozygotes are favored 3.Stabilizing – the heterozygotes are favored

Question 29

what is fitness value (w)? formula?

Answer 29

individual's capability to reproduce w = 1-s

Question 30

2 general types of SELECTION + which acts before fertilization? + which acts after fertilization?

Answer 30

1. Gametic selection – environment prevents participation of gametes carrying a specific allele in fertilization (BEFORE FERTILIZATION) 2. Zygotic selection – environment prevents participation of individuals with a specific genotype in mating (AFTER FERTILIZATION)

Question 31

memorize selection table formulas

Question 32

MIGRATION formula

Answer 32

(1-m)^n = (qn - Q) / (q0 - Q) wherein n = number of generations with migration q0 = frequency of the allele in the recipient population Q = frequency of the allele in the migrant population qn = frequency of the allele in the mixed population m = (Nmigrants) / (Nmigrants + Nrecipients)

Question 33

Dispersive factors are due to?

Answer 33

sampling errors in the population

Question 34

2 types of GENETIC DRIFT

Answer 34

a. Bottleneck effect – the effect when an original population is drastically reduced in size (a bottlenecking event) b. Founder effect – the effect when a few individuals become isolated from a large population and establish a new population with a different gene pool

Question 35

"____ proposes while ____ disposes"

Answer 35

mutation selection

Question 36

- for small population, drift is _____ - for large population, drift is _____

Answer 36

- significant - negligible

Question 36

3 IMPORTANT FACTORS to recipient population in MIGRATION

Answer 36

1. difference in gene frequencies of recipient population and migrant group 2. proportion of migrant genes 3. number of generations of migration

Question 37

random genetic drift causes (2)?

Answer 37

1. homozygosity 2. loss of genetic diversity

Question 38

AUTHOR Founder Effect: If small number of individuals migrate into a new location, they become founder of a new population.

Answer 38

Mayr

Question 39

WHAT is the - mating between individuals with common ancestry? + example group who did this?

Answer 39

INBREEDING - practiced by "dunkers" (small religous group from german that settled in pennsylvania)

Question 40

4 consequences of inbreeding?

Answer 40

1. genetic uniformity 2. reduced vigor 3. reduced viability 4. reduced fertility

Question 41

inbreeding depression VS inbreeding coefficient?

Answer 41

INBREEDING DEPRESSION - appearance of deleterious phenotypes INBREEDING COEFFICIENT - probability that any two alleles at a locus are alike by descent

Question 42

divergence within a population occurs due to (5)?

Answer 42

1. appearance of new unfilled ecological niches 2. mutation 3. selection pressure 4. migration 5. genetic drift

Question 43

WHAT refers to a genetically distinct population of the same species that differ in the relative frequency of some genes .... it is a consequence of (3)?

Answer 43

RACE 1. geographic isolation 2. genetic drift 3. adaptation to local conditions

Question 44

is race formation a reversible process?

Answer 44

yes

Question 45

race can lead to??

Answer 45

species formation

Question 46

Speciation can occur if there is (3)?

Answer 46

1. permanent geographical barriers 2. acquisition of new genes through mutation 3. sexual isolation

Question 47

2 types of speciation?

Answer 47

1. Allopatric speciation - species that inhabit separate geographic region 2. Sympatric speciation - species that inhabit at least in part the same geographic region