4.4Unit 4: Energy, Environment, Microbiology and Immunity
Evolution — IAL Edexcel Linear Revision Notes & Topical Questions
5 min read 13 parts Lesson 5 of 28 1 quiz
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Lesson summary
4.4 Evolution — IAL EDEXCEL LINEAR notes: Explain how natural selection changes allele frequencies, how isolation leads to speciation, and how molecular evidence and the scientific community support evolution and classification.Evolution = change in the heritable characteristics …
- Sources of variation
- Allele frequency
- Rabbit example
- Types of selection
- Observed examples
- Assumptions
Part 1 of 11Evolution and heritable variation
Evolution
Evolution change in the heritable characteristics of organisms over generations.
- Non-heritable changes, such as a plant having its leaves eaten or gaining weight, do not lead to evolution.
- Heritable characteristics are determined by alleles, which can change by random mutation and become more or less advantageous.
Sources of variation
- Sources of variation mutation, meiosis (independent assortment and crossing over) and random fertilisation.
- (the only source of new alleles)
Allele frequency
Allele frequency number of copies of an allele ÷ total number of alleles of that gene in the population, a value from 0 to 1.
Gene pool
Gene pool all the alleles of all genes in a population at a given time.
Part 2 of 11Natural selection
- Natural selection = the process by which better-adapted organisms survive, reproduce and pass on advantageous alleles,
- so those characteristics increase in frequency.
1
Variation is present in the population.
2
Environmental factors such as predation, competition for food and disease act as selection pressures.
3
Individuals with advantageous alleles are more likely to survive to adulthood, find a mate and have more offspring.
4
They pass the advantageous alleles to their offspring.
5
The advantageous alleles become more frequent, and unfavourable ones become less frequent.
Natural selection
Rabbit example
- Rabbit example brown rabbits are better camouflaged from foxes, so brown fur alleles increase in frequency over generations.
Wording
- Wording evolution acts on random variation and is not a purposeful response to need,
- so say it occurs by natural selection and populations, not individuals, evolve.
Types of selection
- Types of selection directional selection shifts the mean phenotype, stabilising selection favours the mean and reduces variation,
- and disruptive selection favours both extremes.
Observed examples
- Observed examples antibiotic-resistant bacteria such as MRSA, insecticide-resistant insects and peppered moth colour change with industrial pollution.
Part 3 of 11Hardy-Weinberg and allele frequency
Equations
- Equations p + q = 1 and p² + 2pq + q² = 1.
- p and q are the frequencies of the two alleles, and p², 2pq and q² are the frequencies of the genotypes.
Assumptions
- Assumptions a large population with random mating and no selection, mutation or migration.
- A change in allele frequency over generations shows that one of these has occurred.
Part 4 of 11Isolation and speciation
- Speciation = development of new species from existing species over time.
- Two populations must be isolated so there is no gene flow between them.
- Different selection pressures, mutations and genetic drift (random change in allele frequencies, strongest in small populations) change their allele frequencies.
- Eventually the populations differ physiologically, behaviourally and morphologically and can no longer interbreed to produce fertile offspring.
Part 5 of 11Allopatric speciation
- Allopatric speciation speciation after geographical isolation, the most common type.
1
One interbreeding population shares a single gene pool.
2
A natural barrier (water, a new mountain range) or a man-made one (a motorway) splits it into two populations, and gene flow stops.
3
Each environment has different selection pressures, and different mutations and drift occur.
4
Allele frequencies diverge over many generations, changing phenotypes and breeding behaviour.
5
Even if the barrier is removed, the populations cannot interbreed to give fertile offspring, so they are separate species.
- Example
- a new mountain range divides a population of trees, and over thousands of years two distinct species form.
Part 6 of 11Sympatric speciation
1
Sympatric speciation
Sympatric speciation speciation without a geographical barrier, where random allele changes stop some individuals breeding with the rest.
- Seasonal isolationdifferent mating or flowering seasons.
- Mechanical isolationreproductive parts no longer match.
- Behavioural isolationcourtship behaviour no longer attracts mates.
2
Process
- Process the populations share a habitat but do not interbreed, so allele frequencies diverge as in allopatric speciation.
- In plants, polyploidy can create instant isolation.
3
Example
- Example a mutation changing food preference splits a laboratory fruit fly population into two populations that stop interbreeding.
Part 7 of 11Molecular evidence and bioinformatics
1
Sequence comparison
- Sequence comparison species with a more recent common ancestor have fewer differences in DNA base sequences and in amino acid sequences of proteins such as cytochrome c and haemoglobin.
- Percentage difference number of differences ÷ total bases or amino acids compared × 100.
- DNA can be compared by sequencing or by DNA hybridisation, in which the temperature needed to separate hybrid strands shows similarity.
2
Bioinformatics
Bioinformatics the use of computer software and databases to store, align and analyse biological data such as sequences.
- It builds phylogenetic trees and compares large numbers of sequences quickly.
Part 8 of 11Classification and the three domains
Classification and the three domains
Classification
- Classification it has changed as evidence accumulated, and species names use the binomial system.
- (genus and species, in italics)
Three domains
- Woese's rRNA sequence data showed that prokaryotes form two very different groups.
- The domains are Bacteria, Archaea and Eukarya, and Archaea have histones and features closer to eukaryotes.
- The three-domain system replaced the five-kingdom system.
Species concept
- Species concept the biological species concept is hard to apply to asexual organisms, fossils and hybridising species,
- so morphological and molecular data are also used.
Part 9 of 11How the scientific community validates evidence
Peer review
- Peer review other scientists check the methods and conclusions before a paper is published in a scientific journal.
Conferences
- Conferences new data are presented and critically evaluated by the community.
Replication
- Replication independent repeats by other scientists confirm findings.
Limit
- Limit these checks reduce bias but cannot guarantee that a conclusion is correct.
Part 10 of 11More from the specification
1
Metabolic expenditure and adaptation energy
- Metabolic expenditure and adaptation energy advantageous phenotypic traits optimize cellular energy allocation, enhancing survival and reproductive success in challenging environments.
2
Evolution
- Evolution natural selection acts on variation caused by mutation, so advantageous alleles become more frequent
3
Climate change
- Climate change carbon dioxide released from burning fossil fuels increases the greenhouse effect in the atmosphere
4
Global warming
- Global warming higher atmospheric carbon dioxide traps heat and shifts the habitats and selection pressures on species
5
Adaptation
- Adaptation populations change in response to selection over generations, which can lead to speciation
6
Climate
- Average weather of a place over a long time.
7
Atmosphere
- Layer of gas above the Earth's surface.
8
Growth
- A permanent increase in size.
9
Enzyme
- A protein that acts as a biological catalyst.
10
Global warming
- Rise in the Earth's temperature from more greenhouse gases.
11
Fossil fuel
- Fuel such as coal, oil or gas made from long-dead organisms.
12
Carbon cycle
- The movement of carbon between the air, living things, oceans and fossil fuels.
13
Greenhouse effect
- Warming of the atmosphere by gases that trap infrared radiation.
Part 11 of 11More on this topic
- Effects on organisms
- changes in temperature and rainfall alter species ranges, breeding times and food web interactions.
- Organisms with suitable heritable variation are more likely to survive and reproduce.
- Isolated populations can diverge over many generations.
Key terms
| Term | Meaning |
|---|---|
| Evolution | Change in the heritable characteristics of organisms over generations. |
| Allele frequency | The proportion of an allele among all alleles of that gene in a population. |
| Selection pressure | An environmental factor affecting survival and reproduction. |
| Genetic drift | Random change in allele frequencies, strongest in small populations. |
| Allopatric speciation | Formation of new species after geographical isolation. |
| Sympatric speciation | Formation of new species without a geographical barrier. |
| Bioinformatics | Use of computers and databases to store and analyse biological data. |
| Peer review | Checking of research by other scientists before publication. |
Avoid these mistakes
1
Saying individual organisms evolve to meet a need — random variation is selected and populations change.
2
Saying acquired characteristics are inherited — only heritable alleles are passed on.
3
Saying allopatric speciation needs no barrier — it needs geographical isolation, whereas sympatric speciation does not.
4
Treating the five-kingdom system as current — molecular evidence led to the three domains.
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