Evolution Revision Notes
Lecture 7 – Evidence for evolution
Why is evolution important?
It explains:
- Diversity: The enormous range of animals and plants.
- Adaptation: The way each organism “fits” its environment.
- It is the defining concept in Biology.
- Evolution is the only subject that is truly biological because only living systems evolve.
- “Nothing in Biology makes sense except in the light of evolution”.
The role of science
- To increase our understanding of ourselves and the world around us.
Scientific method:
1. Pattern
2. Explanation
3. Test/evidence
Scientific method and evolution:
1. Look for patterns: diversity/unity/adaptation.
2. Produce a testable theory for that pattern.
Theories of the history of life
- Creationism: Humans appeared at some point in time and haven’t changed since.
- Transformism: Diversity we see today is the same as in the past but there can be changes. Change over time
(individual species).
- Evolution: Adaptation, selection pressures, natural selection. Evolving to fit the changing world.
Are changes evident over time?
- Peppered moth – In the last 150 years the melanic form has increases from rarest to most common.
Artificial selection:
- Species: A group of organisms that have similar genotypes and can interbreed to produce fertile offspring.
- Morphological features, fertile offspring.
- Dogs have been artificially selected.
- Can be interbred so they aren’t distinctly different species but morphologically they are very variable.
Has man ever selected a new species?
- Primula kewensis (primula plant).
- Will not produce fertile offspring.
- Crossed an 18-chromosome plant with another 18-chromosome plant and gave a plant with 36-chromosomes.
Double the usual number of chromosomes.
- Species aren’t fixed, it is very difficult to define a species.
Are changes evident in space?
- Clinal variation: A gradual change in a character or feature across the distributional range of a species or
population, usually correlated with an environmental or geographic transition.
- Longitudinal distribution: Up and down.
- Latitudinal distribution: Across.
- Reproduce along the stages. In the middle of the cline they are all separate species but at the edges they
interbreed.
Changes in the past – the evolution of horses
- Run on a single digit.
- Teeth specialised for eating grass.
- Responses to environmental change.
- Changes in the past disprove creationism and transformism theories.
,Classification and homology
- Classification is based on homologous structures in an organism’s phenotype.
- Structures that don’t share a common function (e.g. wings – bats, insects, birds, etc).
- Homologous characters: Traits that are inherited from a common ancestor (but may now serve different
functions).
The universal homology
- Can be used to transfer DNA to amino acids – proteins.
- All living organisms share the same genes.
- Genetic code is universal.
- Darwin’s finches
1. Large ground finch: Crushes large, hard seeds.
2. Cactus finch: Opens cactus fruits and extracts seeds.
3. Vegetarian finch: Wrenches buds from branches.
4. Woodpecker finch: Probes dead wood for insects.
5. Warbler finch: Picks insects from leaves.
- Conclusion: Form of species isn’t fixed and species aren’t distinct in time and space.
Lecture 8 – Mechanisms of evolution
- Evolution: Any change in gene frequency.
- Gene frequency: Proportional representation of a gene in the population.
- Frequency of allele = number of alleles of that type / total
- A = 16/20 = 0.8
- Usually expressed as a proportion rather than a percentage.
Mendelian inheritance
- Pure bred: Guarantee that seeds produced will be the same as those of the parent plant.
- One of the core principles of Darwin’s evolutionary theory.
1. Heredity isn’t blending. Only works if the things determining genotype are particulate. Can’t get a ½ smooth, ½
wrinkled pea.
2. Acquired characteristics aren’t inherited.
- E.g. Covering a green pea and it goes yellow but acquired characteristics don’t pass onto offspring.
Weismann’s principle
Germ cell (gamete) germ cell germ cell (haploid)
- Only way information can be passed from one generation to another. Influences soma – phenotype.
Germ cell (gamete) soma (everything else) soma soma (diploid)
- Can change the soma all you want but won’t have an influence on the offspring.
The central dogma
DNA protein
3. It doesn’t produce a directional change in gene frequency as a result of mendelian inheritance.
- Genotype frequencies are changing but gene frequencies aren’t changing.
Hardy-Weinberg equilibrium
- The gene frequency in a population that isn’t evolving.
- Describes what happens when there is no evolutionary change in a population.
- Gene frequencies don’t change (no evolution).
- Conditions:
1. Infinite population size (no genetic drift)
2. No mutation
3. Mendelian inheritance
4. No selection
5. Random mating
, Genetic drift
- Occurs because mendelian inheritance isn’t exact.
- Produces changes in gene frequency.
- More likely to occur in small populations.
- The effect of small variations in a small population is more pronounced.
- If a population is <100 drift is very important.
- If a population is >100,000 drift is negligible/unimportant.
- E.g. Human blood groups in Italy. Blood group frequencies vary a lot between villages and they are similar
between cities.
Mutation:
- A heritable change in genetic material.
- May involve a change in a chromosome or a change in a single gene.
- Mutation occurs at a very low rate so is relatively unimportant as a mechanism of evolution.
- Very low rate.
Non-Mendelian inheritance
1. Meiotic drive:
- Meiotic drive genes distort gene segregations so that gametes that don’t carry the meiotic drive genes die.
- Changes in gene frequency – evolution taking place.
- E.g. Segregation distorter gene in Drosophila.
- Incredibly rare.
2. Molecular drive:
- Molecular drive genes are able to convert slightly different genes into identical copies of themselves.
- Very rare.
- Evolution – gene frequency changes.
3. Inheritance of acquired characteristics (Lamarckism):
- Was thought that characters acquired during their lifetimes would be passed onto offspring.
- No proposed mechanisms for how this works.
- Experiments investigating this either done with unintentional design flaws or faked.
Selection
- Occurs when genotypes differ in their ability to pass genes on to the next generation.
- If a genotype is successful then its genes will increase in frequency.
- If a genotype is unsuccessful then its genes will decrease in frequency.
3 types of selection:
1. Artificial selection:
- Practical reason for the selection of a certain type of animal.
- Animals with the phenotype that you want are selected for.
2. Natural selection:
- Traits that enhance survival.
- Parental care – looking after offspring makes offspring more likely to survive.
3. Sexual selection:
- Drives non-random reproduction.
- Most sexually-reproducing organisms have sexually selective traits.
- Display traits; makes organisms more attractive, usually males.
- Competition directly between males – selects for weapons.
- Acts against natural selection.
Lecture 9 – Mechanisms of adaptation
- Evolution: Any change in gene frequencies.
- Adaptation: Evolutionary change that fits an animal to its habit or habitat.
Lecture 7 – Evidence for evolution
Why is evolution important?
It explains:
- Diversity: The enormous range of animals and plants.
- Adaptation: The way each organism “fits” its environment.
- It is the defining concept in Biology.
- Evolution is the only subject that is truly biological because only living systems evolve.
- “Nothing in Biology makes sense except in the light of evolution”.
The role of science
- To increase our understanding of ourselves and the world around us.
Scientific method:
1. Pattern
2. Explanation
3. Test/evidence
Scientific method and evolution:
1. Look for patterns: diversity/unity/adaptation.
2. Produce a testable theory for that pattern.
Theories of the history of life
- Creationism: Humans appeared at some point in time and haven’t changed since.
- Transformism: Diversity we see today is the same as in the past but there can be changes. Change over time
(individual species).
- Evolution: Adaptation, selection pressures, natural selection. Evolving to fit the changing world.
Are changes evident over time?
- Peppered moth – In the last 150 years the melanic form has increases from rarest to most common.
Artificial selection:
- Species: A group of organisms that have similar genotypes and can interbreed to produce fertile offspring.
- Morphological features, fertile offspring.
- Dogs have been artificially selected.
- Can be interbred so they aren’t distinctly different species but morphologically they are very variable.
Has man ever selected a new species?
- Primula kewensis (primula plant).
- Will not produce fertile offspring.
- Crossed an 18-chromosome plant with another 18-chromosome plant and gave a plant with 36-chromosomes.
Double the usual number of chromosomes.
- Species aren’t fixed, it is very difficult to define a species.
Are changes evident in space?
- Clinal variation: A gradual change in a character or feature across the distributional range of a species or
population, usually correlated with an environmental or geographic transition.
- Longitudinal distribution: Up and down.
- Latitudinal distribution: Across.
- Reproduce along the stages. In the middle of the cline they are all separate species but at the edges they
interbreed.
Changes in the past – the evolution of horses
- Run on a single digit.
- Teeth specialised for eating grass.
- Responses to environmental change.
- Changes in the past disprove creationism and transformism theories.
,Classification and homology
- Classification is based on homologous structures in an organism’s phenotype.
- Structures that don’t share a common function (e.g. wings – bats, insects, birds, etc).
- Homologous characters: Traits that are inherited from a common ancestor (but may now serve different
functions).
The universal homology
- Can be used to transfer DNA to amino acids – proteins.
- All living organisms share the same genes.
- Genetic code is universal.
- Darwin’s finches
1. Large ground finch: Crushes large, hard seeds.
2. Cactus finch: Opens cactus fruits and extracts seeds.
3. Vegetarian finch: Wrenches buds from branches.
4. Woodpecker finch: Probes dead wood for insects.
5. Warbler finch: Picks insects from leaves.
- Conclusion: Form of species isn’t fixed and species aren’t distinct in time and space.
Lecture 8 – Mechanisms of evolution
- Evolution: Any change in gene frequency.
- Gene frequency: Proportional representation of a gene in the population.
- Frequency of allele = number of alleles of that type / total
- A = 16/20 = 0.8
- Usually expressed as a proportion rather than a percentage.
Mendelian inheritance
- Pure bred: Guarantee that seeds produced will be the same as those of the parent plant.
- One of the core principles of Darwin’s evolutionary theory.
1. Heredity isn’t blending. Only works if the things determining genotype are particulate. Can’t get a ½ smooth, ½
wrinkled pea.
2. Acquired characteristics aren’t inherited.
- E.g. Covering a green pea and it goes yellow but acquired characteristics don’t pass onto offspring.
Weismann’s principle
Germ cell (gamete) germ cell germ cell (haploid)
- Only way information can be passed from one generation to another. Influences soma – phenotype.
Germ cell (gamete) soma (everything else) soma soma (diploid)
- Can change the soma all you want but won’t have an influence on the offspring.
The central dogma
DNA protein
3. It doesn’t produce a directional change in gene frequency as a result of mendelian inheritance.
- Genotype frequencies are changing but gene frequencies aren’t changing.
Hardy-Weinberg equilibrium
- The gene frequency in a population that isn’t evolving.
- Describes what happens when there is no evolutionary change in a population.
- Gene frequencies don’t change (no evolution).
- Conditions:
1. Infinite population size (no genetic drift)
2. No mutation
3. Mendelian inheritance
4. No selection
5. Random mating
, Genetic drift
- Occurs because mendelian inheritance isn’t exact.
- Produces changes in gene frequency.
- More likely to occur in small populations.
- The effect of small variations in a small population is more pronounced.
- If a population is <100 drift is very important.
- If a population is >100,000 drift is negligible/unimportant.
- E.g. Human blood groups in Italy. Blood group frequencies vary a lot between villages and they are similar
between cities.
Mutation:
- A heritable change in genetic material.
- May involve a change in a chromosome or a change in a single gene.
- Mutation occurs at a very low rate so is relatively unimportant as a mechanism of evolution.
- Very low rate.
Non-Mendelian inheritance
1. Meiotic drive:
- Meiotic drive genes distort gene segregations so that gametes that don’t carry the meiotic drive genes die.
- Changes in gene frequency – evolution taking place.
- E.g. Segregation distorter gene in Drosophila.
- Incredibly rare.
2. Molecular drive:
- Molecular drive genes are able to convert slightly different genes into identical copies of themselves.
- Very rare.
- Evolution – gene frequency changes.
3. Inheritance of acquired characteristics (Lamarckism):
- Was thought that characters acquired during their lifetimes would be passed onto offspring.
- No proposed mechanisms for how this works.
- Experiments investigating this either done with unintentional design flaws or faked.
Selection
- Occurs when genotypes differ in their ability to pass genes on to the next generation.
- If a genotype is successful then its genes will increase in frequency.
- If a genotype is unsuccessful then its genes will decrease in frequency.
3 types of selection:
1. Artificial selection:
- Practical reason for the selection of a certain type of animal.
- Animals with the phenotype that you want are selected for.
2. Natural selection:
- Traits that enhance survival.
- Parental care – looking after offspring makes offspring more likely to survive.
3. Sexual selection:
- Drives non-random reproduction.
- Most sexually-reproducing organisms have sexually selective traits.
- Display traits; makes organisms more attractive, usually males.
- Competition directly between males – selects for weapons.
- Acts against natural selection.
Lecture 9 – Mechanisms of adaptation
- Evolution: Any change in gene frequencies.
- Adaptation: Evolutionary change that fits an animal to its habit or habitat.
