Variation, selection, evolution and classification
By the end of this chapter you will be able to
- Distinguish genetic and environmental variation, and continuous and discontinuous variation
- Describe selective breeding and genetic engineering, and weigh their advantages and risks
- Explain natural selection step by step, and how it leads to evolution
- Classify an organism using the Linnaean ranks
- [H] Explain how extinction happens, and what fossils can and cannot show
You should already know
- DNA, genes and alleles (Chapter 15)
- Mutation and antibiotic resistance (Chapter 14)
- Percentages (Chapter 1)
Where this leads
- Ecology and biodiversity (Chapters 17 and 18)
- Human impact on species (Chapter 18)
- Plant breeding and yield (Chapter 8)
GCSE Biology. Content follows the GCSE (9-1) subject content for England (Edexcel and AQA). Content references: Describe genetic and environmental variation, and continuous and discontinuous variation, Describe selective breeding and genetic engineering, with their advantages and risks, Explain natural selection and the theory of evolution by Darwin, Explain antibiotic resistance as an example of natural selection, extinction and what fossils show, Describe Linnaean classification and the three domains of life (idea), [H] Explain extinction in more detail.
Exercise P Do you remember?
Method. Recall the molecule.
- Recall. DNA carries the genetic information.genetic information
- Write the answer. DNA
Check. DNA is found in the nucleus. ✓
Method. Work out 10 percent, then multiply by 4.
- 10 percent. 10% of 40 is 4.4
- 40 percent. 4 x 4 = 16.16
- Write the answer. 16
Check. 16 out of 40 is 40%. ✓
Method. Recall the definition.
- Recall. A mutation is a random change in DNA.random change
- Write the answer. a random change
Check. Mutations are the source of new alleles. ✓
Method. Recall the process.
- Recall. Survivors reproduce and become more common, which is natural selection.natural selection
- Write the answer. natural selection
Check. Antibiotics are the selection pressure. ✓
Method. Multiply.
- Multiply. 2 x 2 = 4, then 4 x 2 = 8.8
- Write the answer. 8
Check. 8 divided by 2 is 4. ✓
Variation: genetic, environmental, continuous and discontinuous
Variation is the difference between individuals of the same species. It has two main causes: genetic variation, from the alleles inherited from the parents, and environmental variation, from the conditions that an organism lives in, such as diet or sunlight. Many features are caused by both.
Continuous variation is when a characteristic can take any value within a range, such as height. Many genes and the environment combine to produce it, so the values form a smooth range. Discontinuous variation is when there are a few distinct categories, such as blood group, usually controlled by a small number of genes.
Key ideas
- Variation is the difference between individuals of a species.
- Genetic variation comes from inherited alleles; environmental variation from conditions.
- Continuous variation has a range of values, such as height.
- Discontinuous variation has distinct categories, such as blood group.
Method. Decide whether values form a range or categories.
- Look. Blood groups are distinct categories, with no values in between.distinct categories
- Name it. So the variation is discontinuous.discontinuous
- Write the answer. discontinuous
Check. Height is continuous. ✓
Method. Decide whether values form a range.
- Look. Height can take any value in a range.any value in a range
- Name it. So the variation is continuous.continuous
- Write the answer. continuous
Check. Many genes and the environment contribute. ✓
Method. Find the tallest bar.
- Look. The 170-179 band has the tallest bar, with 15 students.15 students
- Name it. So the band with the most students is 170-179 cm.170-179
- Write the answer. 170-179
Check. The bars form a range. ✓
Watch out
Watch out: a feature with a range of values is not always continuous. Continuous variation means any value in a range; discontinuous means distinct categories.
Exam tip
Exam tip. Name the type of variation, then give an example that shows it.
Try it (with your teacher). With your teacher, measure the heights of five people in your class, and put them into 10 cm bands. Say whether the variation looks continuous or discontinuous.
Exercise 16A Variation: genetic, environmental, continuous and discontinuous
Method. Recall the cause.
- Recall. Inherited alleles cause genetic variation.inherited alleles
- Write the answer. genetic variation
Check. Environmental variation comes from conditions. ✓
Method. Recall the cause.
- Recall. Diet and other conditions cause environmental variation.conditions
- Write the answer. environmental variation
Check. Many features have both causes. ✓
Method. Recall the type.
- Recall. Height can take any value in a range.any value in a range
- Name it. So it is continuous.continuous
- Write the answer. continuous
Check. Blood group is discontinuous. ✓
Method. Recall the type.
- Recall. Blood group has distinct categories.distinct categories
- Name it. So it is discontinuous.discontinuous
- Write the answer. discontinuous
Check. There are no blood groups between A and B. ✓
Method. Read the bar.
- Read. The 160-169 bar shows 12 students.12
- Write the answer. 12
Check. The total of all bands is 40. ✓
Method. Add the bars.
- Add. 5 + 12 + 15 + 8 = 40.5 + 12 + 15 + 8 = 40
- Write the answer. 40
Check. The total matches the class size. ✓
Method. Divide the count by the total, then multiply by 100.
- Divide. 16 / 40 = 0.4.16 / 40 = 0.4
- Multiply. Multiply by 100: 40%.40%
- Write the answer. 40%
Check. 40% of 40 is 16. ✓
Method. Think about what affects growth.
- Think. Diet, illness and exercise can all affect growth.affect growth
- Choose one. Any one of these is a correct answer.any one
- Write the answer. Accept any one: diet, illness, or exercise.
Check. Environment and genes both matter. ✓
Method. Think about the causes of variation.
- Think. Identical twins have the same genes, so genetic variation is absent.same genes
- Conclude. Differences must then come from environmental variation, such as diet.environmental variation
- Write the answer. Accept any sentence that says environmental factors such as diet can cause differences even with the same genes.
Check. Genes alone do not decide the features. ✓
Method. Combine the genes and the environment.
- Genes. Many genes each contribute a small amount to a feature such as height.many genes
- Environment. Environmental factors also vary, adding to the range.also vary
- Conclude. So the combined effect gives a smooth range of values.smooth range
- Write the answer. Accept any answer that says many genes each contribute a little, and the environment also varies, giving a range of values.
Check. Continuous variation comes from many small effects. ✓
Selective breeding and genetic engineering
Selective breeding (artificial selection) chooses parents with a desired characteristic and breeds them, then repeats this over many generations. It can produce plants and animals with high yields or useful features, but it can reduce genetic variety and cause inherited health problems.
Genetic engineering cuts a gene from one organism, inserts it into a vector such as a plasmid, and puts it into the cells of another organism. The new organism then makes the protein the gene codes for. Examples include bacteria that make human insulin, and crops that resist pests.
| Selective breeding | Advantage | Risk |
|---|---|---|
| dairy cows with high milk yield | more milk for the same number of cows | less genetic variety; health problems |
| wheat with disease resistance | fewer crops lost to disease | the population may become vulnerable to a new disease |
| dogs bred for a shape | a desired appearance | inherited health problems |
| Use | Advantage | Concern |
|---|---|---|
| insulin made by GM bacteria | a reliable, pure supply for people with diabetes | few; widely accepted |
| GM crops resistant to pests | less pesticide and more food | effects on other wildlife; gene spread |
| gene therapy | may cure an inherited condition | still being researched; delivery is difficult |
Key ideas
- Selective breeding chooses parents with a desired trait, over generations.
- Its risks include lower genetic variety and inherited health problems.
- Genetic engineering inserts a gene into another organism.
- GM uses include insulin from bacteria, pest-resistant crops and gene therapy.
Method. Recall the method.
- Recall. Breeding only from organisms with a desired characteristic is selective breeding.selective breeding
- Name it. Selective breeding is also called artificial selection.artificial selection
- Write the answer. selective breeding (artificial selection)
Check. It is done by humans over generations. ✓
Method. Recall the risks.
- Recall. Selective breeding can reduce genetic variety.reduce genetic variety
- Name it. So a risk is less genetic variety.genetic variety
- Write the answer. less genetic variety
Check. Inherited health problems are another risk. ✓
Method. Recall the carrier.
- Recall. A plasmid is a small ring of DNA used as a vector.a vector
- Name it. So the vector is a plasmid.plasmid
- Write the answer. plasmid
Check. The gene is inserted into the plasmid first. ✓
Watch out
Watch out: selective breeding uses variation that already exists, over generations. Genetic engineering moves a gene directly, from one organism into another.
Exam tip
Exam tip. When you weigh the advantages and risks of GM, give one of each and say why it matters.
Try it (with your teacher). With your teacher, find two examples of selectively bred plants or animals. For each one, write one advantage and one risk, with no names of companies or products.
Exercise 16B Selective breeding and genetic engineering
Method. Recall the method.
- Recall. Selective breeding uses parents with desired characteristics.desired characteristics
- Write the answer. selective breeding
Check. It is also called artificial selection. ✓
Method. Recall the process.
- Recall. Genetic engineering moves a gene into another organism.moves a gene
- Write the answer. genetic engineering
Check. The gene is inserted into a vector first. ✓
Method. Recall the vector.
- Recall. A plasmid is a small ring of DNA used as a vector.small ring of DNA
- Write the answer. plasmid
Check. Plasmids are found in bacteria. ✓
Method. Recall the example.
- Recall. Bacteria can be genetically engineered to make human insulin.make human insulin
- Write the answer. insulin
Check. Insulin treats diabetes. ✓
Method. Recall the risks.
- Recall. Selective breeding can reduce genetic variety and cause inherited health problems.reduce genetic variety
- Choose one. Either risk is a correct answer.either
- Write the answer. Accept any one: less genetic variety, or inherited health problems.
Check. Both are important. ✓
Method. Recall the therapy.
- Recall. Gene therapy replaces a faulty allele in a person’s cells.replaces a faulty allele
- Write the answer. gene therapy
Check. It is still being researched. ✓
Method. Think about the effect on the crop.
- Think. A crop that resists pests loses less to them.loses less
- Conclude. So less pesticide is needed, and more food can be grown.more food
- Write the answer. Accept any sentence that says less pesticide is needed and more food can be grown.
Check. Other effects, such as on wildlife, must also be weighed. ✓
Method. Think about the wider effects.
- Think. A new gene in a crop may spread to wild plants, or affect other animals.spread
- Conclude. These wider effects must be considered before GM crops are used.considered
- Write the answer. Accept any sentence that says they may affect other wildlife, or the gene may spread to wild plants.
Check. Balance the advantages and risks. ✓
Method. Match the method to the description.
- Match. Choosing the highest-yielding parents and repeating is selective breeding.highest-yielding
- Name it. So the method is selective breeding.selective breeding
- Write the answer. selective breeding
Check. Genetic engineering is not needed here. ✓
Method. Think about which individuals breed.
- Think. Only a few selected individuals are used as parents.only a few
- Conclude. The alleles of the others are not passed on, so variety falls.alleles of the others
- Write the answer. Accept any sentence that says only a few parents are used each generation, so the alleles of the others are lost.
Check. Fewer parents mean fewer alleles. ✓
Method. Compare the sources.
- Human. The bacteria make a human protein, which matches human insulin closely.human protein
- Supply. The supply is reliable and pure, avoiding some risks from animal sources.reliable and pure
- Write the answer. Accept any answer that says it is a pure human protein supplied in a reliable way, which avoids some risks of animal sources.
Check. Balance the benefits with any other concerns. ✓
Natural selection and evolution
Natural selection is a process in which individuals with characteristics that suit the environment survive and reproduce more successfully, so their alleles become more common. It needs variation in the population, which comes from mutation and from genetic recombination in reproduction. A selection pressure is a factor in the environment that affects survival, such as predators, disease or a change in climate.
Darwin and Wallace proposed that species change over time through natural selection, which is the theory of evolution. Over many generations, the population changes and new species can form.
Key ideas
- Natural selection: variation, a selection pressure, survival, then reproduction.
- Mutation creates new alleles; selection pressure acts on the variation.
- Darwin and Wallace proposed evolution by natural selection.
- Evolution is a change in the alleles of a population over many generations.
Method. Recall the source of variation.
- Recall. New alleles come from random changes in DNA.random changes
- Name it. These changes are called mutations.mutations
- Write the answer. mutation
Check. Mutations are random and may have no effect. ✓
Method. Recall the selection pressure.
- Recall. A factor in the environment that affects survival is a selection pressure.selection pressure
- Name one. Predators, disease or a change in climate are examples.predators
- Write the answer. a selection pressure, such as predators
Check. Selection pressures act on variation. ✓
Method. Recall the scientist.
- Recall. Charles Darwin proposed evolution by natural selection.Darwin
- Check. Alfred Russel Wallace reached the same idea independently, so the pair is named together.Wallace
- Name it. So the scientist is Charles Darwin.Charles Darwin
- Write the answer. Charles Darwin
Check. Darwin and Wallace both proposed the idea. ✓
Watch out
Watch out: individuals do not evolve; populations do. An individual does not change its alleles to suit the environment.
Exam tip
Exam tip. Describe natural selection in steps: variation, selection pressure, survival, reproduction, change in the population.
Try it (with your teacher). With your teacher, use a set of paper shapes, some camouflaged on a coloured background. Let a partner remove the shapes they see first, and record how many of each type remain. Describe the result in terms of selection.
Exercise 16C Natural selection and evolution
Method. Recall the process.
- Recall. Natural selection favours individuals with useful characteristics.useful characteristics
- Write the answer. natural selection
Check. It leads to evolution over generations. ✓
Method. Recall the source.
- Recall. Mutations are random changes in DNA that create new alleles.create new alleles
- Write the answer. mutation
Check. Mutations can be harmful, neutral or helpful. ✓
Method. Recall the scientist.
- Recall. Charles Darwin proposed evolution by natural selection.Charles Darwin
- Write the answer. Darwin
Check. Wallace also contributed. ✓
Method. Recall the term.
- Recall. The change in the alleles of a population over generations is evolution.over generations
- Write the answer. evolution
Check. Evolution is a change in populations, not individuals. ✓
Method. Recall the term.
- Recall. A factor in the environment that affects survival is a selection pressure.affects survival
- Write the answer. a selection pressure
Check. Predators are one example. ✓
Method. Think about camouflage.
- Think. Dark moths are harder for birds to see on dark trees.harder to see
- Name it. So dark moths are more likely to survive.dark
- Write the answer. dark
Check. Pale moths are easier to see. ✓
Method. Recall the source of variation.
- Recall. Variation comes from mutations and inherited alleles, not from individuals choosing to change.not from individuals choosing
- Write the answer. So no.no
- Write the answer. no
Check. Natural selection is not a choice. ✓
Method. Think about survival.
- Think. Pale moths are eaten, so fewer of them reproduce.fewer reproduce
- Conclude. Dark moths survive and reproduce more, so the dark allele becomes more common.more common
- Write the answer. increases
Check. The frequency rises over generations. ✓
Method. Recall the steps.
- Recall. The selection pressure acts, and the individuals with useful traits survive.useful traits survive
- Name it. So the step is survival, before reproduction.survival
- Write the answer. survival
Check. Reproduction comes after survival. ✓
Method. Think about what selection acts on.
- Think. Selection acts on differences between individuals.differences
- Conclude. Without variation, all individuals would be the same, so there is nothing to select.nothing to select
- Write the answer. Accept any sentence that says without variation, no individual has a better chance of survival, so there is nothing to select.
Check. Variation is the raw material for selection. ✓
Method. Link the small changes to the total.
- Small. Each generation changes the allele frequencies only a little.only a little
- Add up. Over many generations these small changes add up to a large change.add up
- Write the answer. Accept any answer that says each generation makes a small change in allele frequencies, and these changes add up over time.
Check. Time is what makes the change large. ✓
Antibiotic resistance, extinction and fossils
Antibiotic resistance is a clear example of natural selection. A few bacteria with a resistance mutation survive the antibiotic, and they reproduce, so resistant bacteria become common. The bacteria reproduce quickly, so the change is seen in a few years.
Extinction happens when no individuals of a species remain. [H] It can be caused by habitat loss, climate change, a new predator or disease, or competition with a new species.
Fossils are the remains or traces of past organisms, found in rocks. They show that species have changed over time, but the fossil record is incomplete: most organisms do not form fossils, so gaps remain.
| Feature | Why it matters |
|---|---|
| bacteria reproduce quickly | resistance can appear within a few years |
| fossils form rarely | the record is incomplete, with gaps |
| soft-bodied organisms | rarely preserved as fossils |
Key ideas
- Antibiotic resistance is natural selection, seen quickly in bacteria.
- Extinction happens when no individuals of a species remain.
- [H] Causes of extinction include habitat loss and climate change.
- Fossils show past life, but the record is incomplete.
Method. Recall the process.
- Recall. Resistant bacteria survive and reproduce, which is natural selection.survive and reproduce
- Name it. So the process is natural selection.natural selection
- Write the answer. natural selection
Check. Resistance is a mutation followed by selection. ✓
Method. Recall a cause.
- Recall. Habitat loss, climate change, a new predator or disease can cause extinction.can cause extinction
- Choose one. Any one of these is correct.any one
- Write the answer. Accept any one: habitat loss, climate change, a new predator or disease.
Check. Extinction is the loss of all individuals of a species. ✓
Method. Recall the term.
- Recall. Remains or traces of past organisms in rock are fossils.remains or traces
- Name it. So the word is fossils.fossils
- Write the answer. fossils
Check. Fossils show change over time. ✓
Watch out
Watch out: a fossil record with gaps does not mean that evolution did not happen. Most organisms never form fossils, so gaps are expected.
Exam tip
Exam tip. When you describe antibiotic resistance, use natural selection in steps. When you describe extinction, give a cause and say why it matters.
Try it (with your teacher). With your teacher, look at a labelled picture of a fossil in rock. Describe what the fossil shows about the organism, and what it cannot show.
Exercise 16D Antibiotic resistance, extinction and fossils
Method. Recall the reason.
- Recall. Bacteria reproduce quickly, so resistance spreads in a few years.reproduce quickly
- Write the answer. Accept reproduction.
Check. Quick reproduction speeds up natural selection. ✓
Method. Recall the term.
- Recall. The remains or traces of a past organism in rock are fossils.remains or traces
- Write the answer. fossil
Check. Fossils show past life. ✓
Method. Recall the term.
- Recall. When no individuals of a species remain, the species is extinct.extinct
- Name it. The word is extinction.extinction
- Write the answer. extinction
Check. Extinction is permanent. ✓
Method. Recall the causes.
- Recall. Human activities such as habitat loss and pollution can cause extinction.habitat loss
- Choose one. Either answer is correct.either
- Write the answer. Accept any one: habitat loss, or pollution.
Check. Human causes are discussed in Chapter 18. ✓
Method. Recall how fossils form.
- Recall. Most organisms decay, so only a few form fossils.decay
- Write the answer. So no.no
- Write the answer. no
Check. This is why the fossil record has gaps. ✓
Method. Think about how fossils form.
- Think. Most organisms decay completely, and soft tissue is rarely preserved.decay completely
- Conclude. So only a few organisms leave fossils, and the record has gaps.has gaps
- Write the answer. Accept any sentence that says most organisms decay without forming fossils, and soft tissue is rarely preserved.
Check. Gaps are expected, not a sign of failure. ✓
Method. Think about the time scale.
- Think. Resistance spreads from the first finding within a few years.within a few years
- Conclude. So the change is quick, compared with many generations of other animals.quick
- Write the answer. quick
Check. Bacteria have many generations in a few years. ✓
Method. Think about the habitat.
- Think. A habitat provides food, shelter and places to breed.places to breed
- Conclude. Without it the population falls, and the species may become extinct.may become extinct
- Write the answer. Accept any sentence that says the species loses the places it needs to live and reproduce, so its numbers fall to zero.
Check. The loss may be permanent. ✓
Method. Describe what the record can and cannot show.
- Shows. Fossils show different forms of life over time, so change is evident.different forms
- Limit. Because the record has gaps, many intermediate forms are not found.not found
- Write the answer. Accept any answer that says fossils show different forms over time, but the gaps mean many intermediate forms are missing.
Check. Fossils give evidence, not a complete film. ✓
Classification: Linnaean ranks and the three domains
Classification sorts living things into groups based on shared features. The Linnaean system has a set of ranks, from the broadest to the most specific: kingdom, phylum, class, order, family, genus and species. A species is a group of organisms that can breed to produce fertile offspring. The species name has two parts: the genus, then the species (for example Homo sapiens).
Living things are also grouped into three domains (idea): Bacteria, Archaea and Eukarya. Eukarya includes animals, plants, fungi and protists.
| Rank | Human example |
|---|---|
| kingdom | Animalia |
| phylum | Chordata |
| class | Mammalia |
| order | Primates |
| family | Hominidae |
| genus | Homo |
| species | sapiens |
Key ideas
- Linnaean ranks: kingdom, phylum, class, order, family, genus, species.
- A species can breed to produce fertile offspring.
- The scientific name has two parts: genus, then species.
- Three domains (idea): Bacteria, Archaea and Eukarya.
Method. Recall the first rank.
- Recall. The broadest rank in the Linnaean system is the kingdom.broadest rank
- Name it. So the rank is kingdom.kingdom
- Write the answer. kingdom
Check. Species is the most specific rank. ✓
Method. Recall the last rank.
- Recall. The most specific rank is the species.most specific
- Name it. So the rank is species.species
- Write the answer. species
Check. The species name has two parts. ✓
Method. Recall the two parts.
- Recall. The first part is the genus, and the second is the species.genus, then species
- Name them. So the parts are genus and species.genus and species
- Write the answer. genus and species
Check. Homo is the genus; sapiens is the species. ✓
Watch out
Watch out: the genus name is written with a capital letter, and the species name with a small letter. Both are in italics.
Exam tip
Exam tip. When you classify, name the ranks in order, from kingdom to species. Do not skip any.
Try it (with your teacher). With your teacher, classify three familiar living things, from kingdom down to genus, using the ranks in the chapter.
Exercise 16E Classification: Linnaean ranks and the three domains
Method. Recall the first rank.
- Recall. The broadest rank is the kingdom.broadest rank
- Write the answer. kingdom
Check. Animalia is the kingdom of animals. ✓
Method. Recall the last rank.
- Recall. The most specific rank is the species.most specific
- Write the answer. species
Check. The name has two parts. ✓
Method. Read the table.
- Read. The kingdom of a human is Animalia.Animalia
- Write the answer. Animalia
Check. Humans are animals. ✓
Method. Read the table.
- Read. The genus of a human is Homo.Homo
- Write the answer. Homo
Check. Homo is the first part of the name. ✓
Method. Recall the domains.
- Recall. The three domains are Bacteria, Archaea and Eukarya.three domains
- Write the answer. Bacteria, Archaea and Eukarya
Check. Eukarya includes animals, plants, fungi and protists. ✓
Method. Recall the domain.
- Recall. Eukarya includes organisms whose cells have a nucleus.a nucleus
- Write the answer. Eukarya
Check. Bacteria and archaea do not have a nucleus. ✓
Method. Recall the definition.
- Recall. A species is a group that can breed to produce fertile offspring.fertile offspring
- Write the answer. Accept any sentence that says a species is a group of organisms that can breed to produce fertile offspring.
Check. The definition is based on breeding. ✓
Method. Order the ranks.
- Order. The ranks run kingdom, phylum, class, order, family, genus, species.order, family, genus
- Name it. The rank after family and before species is genus.genus
- Write the answer. genus
Check. Genus comes between family and species. ✓
Method. Use the full list of ranks.
- Order. Kingdom is the broadest, then class, then species.kingdom, class, species
- Write the answer. kingdom, class, species
Check. Class lies between kingdom and species. ✓
Method. Think about the ranks.
- Think. Sharing a genus means the organisms are closely related.closely related
- Conclude. Being different species means they cannot breed to produce fertile offspring.cannot breed
- Write the answer. Accept any sentence that says they are closely related, but cannot breed to produce fertile offspring.
Check. Species is the most specific level. ✓
Method. Compare the groupings.
- Domains. A domain is a broader grouping than a kingdom.broader grouping
- Nesting. So the eukaryote kingdoms, such as animals and plants, sit within the Eukarya domain.within the Eukarya domain
- Write the answer. Accept any answer that says domains are broader groups, and the kingdoms of eukaryotes are placed within the Eukarya domain.
Check. Domains are above kingdoms. ✓
Chapter summary
| Skill | Method |
|---|---|
| Variation | Genetic (inherited alleles) and environmental; continuous (range) and discontinuous (categories). |
| Selective breeding | Parents with a desired trait, repeated over generations; risks include less variety. |
| Genetic engineering | A gene is cut, put into a vector and taken up by a host; examples include insulin and pest-resistant crops. |
| Natural selection | Variation, selection pressure, survival, reproduction; the allele becomes more common. |
| Antibiotic resistance | A worked example of natural selection in bacteria. |
| [H] Extinction | No individuals remain; causes include habitat loss and climate change. |
| Classification | Kingdom, phylum, class, order, family, genus, species; three domains (idea). |
Can you…?
- I can distinguish genetic and environmental variation, and continuous and discontinuous variation
- I can describe selective breeding and genetic engineering, and weigh their advantages and risks
- I can explain natural selection step by step, and how it leads to evolution
- I can classify an organism using the Linnaean ranks
- [H] I can explain extinction, and what fossils can and cannot show
Key terms
- variation
- the differences between individuals of the same species
- continuous variation
- variation with any value within a range, such as height
- discontinuous variation
- variation with distinct categories, such as blood group
- selective breeding
- breeding parents with a desired characteristic over generations
- genetic engineering
- moving a gene from one organism into the cells of another
- natural selection
- the process by which individuals with useful characteristics survive and reproduce more
- evolution
- a change in the alleles of a population over many generations
- fossil
- the remains or traces of a past organism
- [H] extinction
- when no individuals of a species remain
- species
- a group of organisms that can breed to produce fertile offspring
Exercise 16Z Check-up
Method. Recall the cause.
- Recall. Inherited alleles cause genetic variation.inherited alleles
- Write the answer. genetic variation
Check. Environment causes the other type. ✓
Method. Recall the type.
- Recall. Blood group has distinct categories.distinct categories
- Write the answer. discontinuous
Check. Height is continuous. ✓
Method. Recall the method.
- Recall. Selective breeding chooses parents with a desired characteristic.desired characteristic
- Write the answer. selective breeding
Check. It is also called artificial selection. ✓
Method. Recall the vector.
- Recall. A plasmid is used as a vector to carry a gene.used as a vector
- Write the answer. plasmid
Check. Plasmids are small rings of DNA. ✓
Method. Recall the scientist.
- Recall. Darwin proposed evolution by natural selection.proposed evolution
- Write the answer. Darwin
Check. Wallace also contributed. ✓
Method. Recall the source.
- Recall. Mutations are random changes that create new alleles.create new alleles
- Write the answer. mutation
Check. Mutations are random. ✓
Method. Recall the last rank.
- Recall. The most specific rank is the species.most specific
- Write the answer. species
Check. The species name is genus and species. ✓
Method. Read the bar.
- Read. The 170-179 bar shows 15 students.15
- Write the answer. 15
Check. 15 is the largest band. ✓
Method. Recall the term.
- Recall. Remains or traces of past organisms are fossils.remains or traces
- Write the answer. fossils
Check. The fossil record has gaps. ✓
Method. Think about what selection acts on.
- Think. Selection acts on differences between individuals.differences between individuals
- Conclude. Without variation there is nothing to select.nothing to select
- Write the answer. Accept any sentence that says selection acts on differences between individuals.
Check. Variation is the raw material. ✓
Total 26 marks. Allow about 26 minutes.
Exercise 16X Exam-style questions
Method. Recall the type.
- Recall. Distinct categories are discontinuous variation.discontinuous
- Write the answer. discontinuous
Check. Height is continuous. ✓
Method. Recall the process.
- Recall. Genetic engineering moves a gene into another organism.moves a gene
- Write the answer. genetic engineering
Check. Selective breeding uses existing variation. ✓
Method. Recall the domain.
- Recall. Eukarya includes animals, plants, fungi and protists.animals, plants
- Write the answer. Eukarya
Check. Bacteria and archaea are the other domains. ✓
Method. Give two advantages and one risk.
- Advantage 1. GM crops can need less pesticide.less pesticide
- Advantage 2. They can give a higher yield, producing more food.more food
- Risk. The gene may spread to wild plants, or affect wildlife.spread to wild plants
- Write the answer. Accept any three of: less pesticide needed; more food; a risk to wildlife; the gene may spread to wild plants.
Check. Balance the advantages and the risks. ✓
Method. Give the steps in order.
- Variation. There is variation in the population from mutations.variation
- Pressure. A selection pressure acts on the population.selection pressure
- Survival. Individuals with useful alleles survive.survive
- Reproduction. They reproduce, so the allele becomes more common.more common
- Write the answer. Accept any four of: variation exists; a selection pressure acts; individuals with useful alleles survive; they reproduce and pass the alleles on, so the allele becomes more common.
Check. The steps are in order. ✓
Method. Map the steps onto the example.
- Variation. A random mutation gives some bacteria resistance.random mutation
- Pressure. The antibiotic kills the non-resistant bacteria.kills the non-resistant
- Survival. The resistant bacteria survive and reproduce, so resistance becomes common.become common
- Write the answer. Accept any answer that says a mutation gives resistance, the antibiotic kills the non-resistant bacteria, and the resistant survive and reproduce.
Check. Each step matches natural selection. ✓
Method. Read the ranks from the table.
- Kingdom. The kingdom is Animalia.Animalia
- Genus. The genus is Homo.Homo
- Species. The species is sapiens, so the name is Homo sapiens.sapiens
- Write the answer. Accept Animalia, Homo, and sapiens.
Check. The two-part name uses genus and species. ✓
Method. Follow the sequence from habitat loss to extinction.
- Habitat. The species loses the habitat it needs for food and shelter.loses the habitat
- Population. Its population falls because it cannot find food or breed.falls
- Extinction. If no individuals remain, the species becomes extinct.becomes extinct
- Write the answer. Accept any answer that says a species loses its habitat, the population falls because it cannot find food or breed, and if no individuals remain the species is extinct.
Check. Extinction is the end of the sequence. ✓
Method. Give the evidence, then the limit.
- Evidence. Fossils show forms of life from the past, and how they changed.how they changed
- Limit. Most organisms do not form fossils, so the record has gaps.has gaps
- Conclude. So fossils support evolution but do not show every stage.every stage
- Write the answer. Accept any answer that says fossils show past forms and change over time, but most organisms do not form fossils, so the record has gaps.
Check. Evidence has limits. ✓
Method. Compare the method, then the advantage and risk.
- Breeding. Selective breeding uses existing variation over many generations.existing variation
- Engineering. Genetic engineering moves a gene directly into another organism.moves a gene directly
- Advantage. Breeding can give higher yields; engineering can give a pure protein, such as insulin.higher yields
- Risk. Breeding can reduce variety; engineering may have wider effects on wildlife.reduce variety
- Write the answer. Accept any answer that says selective breeding uses existing variation over generations, and genetic engineering moves a gene directly, with one advantage and one risk of each.
Check. The methods differ in how the change is made. ✓