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Population Genetics. Hardy-Weinberg Equilibrium Determination. A B both A and B neither A nor B. Which of these populations are in Hardy-Weinberg equilibrium?. Question 6 – Chap. 23.

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hardy weinberg equilibrium determination
Hardy-Weinberg Equilibrium Determination

A

B

both A and B

neither A nor B

Which of these populations are in Hardy-Weinberg equilibrium?

question 6 chap 23
Question 6 – Chap. 23
  • Researchers examining a particular gene in a fruit fly population discovered that the gene can have either of two slightly different sequences, designated A1 and A2. Further tests showed that 70% of the gametes produced in the population contained the A1 sequence. If the population is at Hardy-Weinberg equilibrium, what proportion of flies carries both A1 and A2?
  • A 0.7 B 0.49 C 0.21 D 0.42 E 0.09
question from an earlier edition of campbell
Question from an earlier edition of Campbell
  • At a locus with a dominant and recessive allele in Hardy-Weinberg equilibrium, 16% of the individuals are homozygous for the recessive allele. What is the frequency of the dominant allele in the population?
  • A 0.84 B 0.36 C 0.6 D 0.4 E 0.48
hardy weinberg equilibrium
Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium is based on:

1. A very large population where all genotypes are equally viable

2. Random mating (panmixia)

3. No mutations

4. No gene flow (dispersal of individuals and their genes)

5. No natural selection

evolutionary change
Evolutionary Change
  • Evolution is a generation to generation change in a population’s frequencies of alleles – change in proportions of alleles in the gene pool is evolution at its smallest scale and is often referred to as microevolution
  • The two main causes of microevolution are genetic drift and natural selection
genetic drift
Genetic Drift
  • Random changes in gene frequency in a population – this can lead to losses in genetic diversity – the population becomes more homozygous
  • this is most important in small populations
genetic drift9

CRCR

CRCR

Genetic Drift

CRCW

CRCR

CWCW

CRCW

CRCR

CRCW

CRCR

CRCW

Generation 1

p (frequency of CR) = 0.7

q (frequency of CW) = 0.3

genetic drift10

5

plants

leave

off-

spring

CWCW

CRCR

CRCR

CRCR

Genetic Drift

CRCW

CRCW

CRCR

CWCW

CWCW

CRCR

CRCW

CRCW

CWCW

CRCR

CRCR

CRCW

CRCW

CRCW

CRCR

CRCW

Generation 1

Generation 2

p (frequency of CR) = 0.7

p = 0.5

q (frequency of CW) = 0.3

q = 0.5

genetic drift11

5

plants

leave

off-

spring

2

plants

leave

off-

spring

CWCW

CRCR

CRCR

CRCR

CRCR

Genetic Drift

CRCW

CRCW

CRCR

CRCR

CRCR

CRCR

CWCW

CRCR

CWCW

CRCR

CRCW

CRCW

CRCR

CRCR

CRCR

CWCW

CRCR

CRCR

CRCW

CRCR

CRCR

CRCW

CRCW

CRCR

CRCW

Generation 1

Generation 2

Generation 3

p (frequency of CR) = 0.7

p = 0.5

p = 1.0

q (frequency of CW) = 0.3

q = 0.5

q = 0.0

slide13

Original

population

slide14

Original

population

Bottlenecking

event

slide15

Original

population

Bottlenecking

event

Surviving

population

slide18

Post-bottleneck

(Illinois, 1993)

Pre-bottleneck

(Illinois, 1820)

Greater prairie chicken

Range

of greater

prairie

chicken

(a)

Percentage

of eggs

hatched

Number

of alleles

per locus

Population

size

Location

Illinois

1930–1960s

1993

5.2

3.7

1,000–25,000

<50

93

<50

Kansas, 1998

(no bottleneck)

750,000

99

5.8

Nebraska, 1998

(no bottleneck)

75,000–

200,000

5.8

96

(b)

slide19

Pre-bottleneck

(Illinois, 1820)

Post-bottleneck

(Illinois, 1993)

Greater prairie chicken

Range

of greater

prairie

chicken

(a)

slide20

Number

of alleles

per locus

Percentage

of eggs

hatched

Population

size

Location

Illinois

1930–1960s

1993

5.2

3.7

1,000–25,000

<50

93

<50

Kansas, 1998

(no bottleneck)

750,000

5.8

99

Nebraska, 1998

(no bottleneck)

75,000–

200,000

5.8

96

(b)

serial founder effect
Serial Founder Effect
  • Serial founder effects have occurred when populations migrate over long distances. Such long distance migrations typically involve relatively rapid movements followed by periods of settlement. The populations in each migration carry only a subset of the genetic diversity carried from previous migrations. As a result, genetic differentiation tends to increase with geographic distance.
gene flow
Gene Flow
  • Gene flow is the movement of alleles in and out of a population
  • Gene flow occurs because gametes or fertile individuals move from one population to another and take their genes with them
slide29

Population in which the

surviving females

eventually bred

60

Central

population

Central

NORTH SEA

Eastern

population

50

Eastern

Vlieland,

the Netherlands

40

2 km

Survival rate (%)

30

20

10

0

Females born

in central

population

Females born

in eastern

population

Parus major

non random mating
Non-Random Mating
  • Hardy-Weinberg assumes random mating – if mating is not random then the population may change in the short term – the most common form of non-random mating is in-breeding – the mating of closely related individuals
  • In fact inbreeding is very common – many mammals probably mate with first or second cousins in the wild; many plants self-pollinate – the ultimate form of inbreeding
  • Inbreeding tends to produce homozygous populations
mutations
Mutations
  • Mutations are the ultimate source of new genetic variations – a new mutation that is transmitted in gametes immediately changes the gene pool of a population by inserting a new allele into the gene pool