evolution and population genetics. population genetics changes in evolution occur in populations,...

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Evolution and Population GENETICS

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Page 1: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Evolution and Population GENETICS

Page 2: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Population GeneticsPopulation Genetics

Changes in evolution occur in populations, not individuals

Page 3: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Population GeneticsBasic Vocaulary

•gene pool

–entire collection of genes in a population

•allele frequency

–number of times an allele appears in a gene pool

•genetic equilibrium

–gene pool which is not changing in allele frequencies

–a population at genetic equilibrium is not evolving

Page 4: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Evolution and Population Genetics

• For a population to evolve, there must be some form of change genetically.

• What are some things that cause change in the gene pool of a population?

Page 5: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

4 Basic Evolutionary Mechanisms

1. Mutation

2. Migration

3. Genetic drift

4. Natural selection

Page 6: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Mutation

•introduces of new alleles into gene pool

Page 7: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

How Mutation Causes Change

• A mutation (change in DNA code) could cause parents with genes for bright green coloration to have offspring with a gene for brown coloration. That would make the genes for brown beetles more frequent in the population.

• Causes of mutations?

Page 8: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Migration

• When individuals of one population move and join a new population

Page 9: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

How Migration Causes Change

• Some individuals from a population of brown beetles might have joined a population of green beetles. That would make the genes for brown beetles more frequent in the green beetle population.

Page 10: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Population Genetics•gene flow

–The movement of alleles from one population to another

–this can change the allele frequency of both populations

Page 11: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Genetic Drift

• random change in allele frequency over time

Page 12: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Causes of Genetic Drift

1.The Bottleneck Effect

•Genetic drift that occurs after an event greatly reduces the sizes of a population

•Numbers of individuals in population are greatly reduced

•Loss of diversity

Page 13: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Causes of Genetic Drift

2. The Founder Effect

•Genetic drift that occurs after a small number of individuals colonize a new area

•Gene pool very different from the larger population

Page 14: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Problems with Genetic Drift

• Loss of genetic diversity

• Less likely for some individuals to adapt to a changing environment

• Lethal and/or harmful alleles carried by heterozygotes and become more common in gene pool

Page 15: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Natural Selection

•Organisms that are better adapted to the environment survive and reproduce

•For larger populations natural selection is the significant factor which causes changes in allele frequency

Page 16: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals
Page 17: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Types of Natural Selection

• Directional- selection for one extreme

• Disruptive- selection for both extremes- against the “middle”

• Stabilizing- selection for the middle- against the extremes

Page 18: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Types of Natural Selection

1. Stabilizing Selection

–selection against extremes, favors the average

Page 19: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Types of Natural Selection

2. Directional Selection

–selection against one extreme, favors other extreme

Page 20: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Types of Natural Selection

3. Disruptive Selection

–selection against average, favors both extremes

Page 21: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Hardy-Weinberg Equilibrium

• Genotype frequencies remain constant in a population as long as certain conditions are met

• Frequencies can be predicted

• Identifies 5 conditions that must be met in order for a population to be in equilibrium

• Populations in equilibrium are not evolving= in Hardy-Weinberg Equilibrium

Page 22: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Hardy-Weinberg Equilibrium

• Very large population (no genetic drift)

• No emigration or immigration (no gene flow)

• No mutations (no new alleles added)

• Random Mating (no sexual selection)

• No natural selection (all traits are equal)

Page 23: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Why Use Hardy-Weinberg?

• Real populations rarely ever meet all 5 conditions!

• Why do you think we use the Hardy-Weinberg model?

Page 24: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Genotype Frequencies

• p2 + 2pq + q2 = 1

• p= frequency of dominant allele

• q= frequency of recessive allele

• p+q = 1 Why?

• What does p2 equal?

• What does 2pq equal?

• What does q2 equal?

Page 25: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Example

• In a population of fish fork tails are dominant over smooth tails.

• You have 1000 fish total in this population.

• 640 of them have forked tails.

• 360 of them have smooth tails.

• What are the genotype frequencies?

Page 26: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Example

• q2= 360 smooth-finned fish out of 1000 total– q2= 360/1000= 0.36

• To find q, take the square root of 0.36= 0.6

• Find P with the equation p + q = 1– So 1- 0.6 = 0.4

• Now we have p= 0.4 and q = 0.6 (allele frequencies)

Page 27: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Example

• Now we have p= 0.4 and q = 0.6 (allele frequencies)

• Calculate the genotype frequencies:– p2 = 0.42 = 0.16 = 16% TT– q2 = 0.62 = 0.36 = 36% tt– 2pq= (2)x(0.4)x(0.6) = 0.48 = 48% Tt

Page 28: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Evolution of a Species

•speciation

–the production of two or more species from one original population

Page 29: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

What Causes Speciation?

1. Geographic Isolation

–physical barrier which separates populations

Page 30: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

What Causes Speciation?

2. Reproductive Isolation

–groups can no longer sexually reproduce

–ex: behavior, mating patterns, physical differences

Page 31: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Speed of Speciation

1. Gradualism

–species evolve at a slow constant rate

Page 32: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Speed of Speciation

2. Punctuated Equilibrium

–rapid significant changes over a short time

Page 33: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Patterns in Evolution

1. Adaptive Radiation

–new species develop from a single common ancestor

Page 34: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Patterns in Evolution

2. Divergent Evolution

–new species develop from a single common ancestor

Page 35: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Patterns in Evolution

3. Convergent Evolution

–different species develop similar traits

Page 36: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Patterns in Evolution

4. Co-evolution

–different species develop traits as a result of a close relationship with the other species

Page 37: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals

Two Types of Evolution

• Microevolution: a change in gene frequency within a population. – Ex. Changes is a

beetle population over a short period of time.

– Ex. Antibacterial resistance

• Macroevolution: evolution above the species level. Large Scale!(Patterns, Speciation)– Ex. Changes in all

beetle populations over a long time

– Ex. Origin of mammals

Page 38: Evolution and Population GENETICS. Population Genetics Changes in evolution occur in populations, not individuals