Evolution is a change in the heritable characteristics of organisms over generations.

Define natural selection .

Natural selection is the process by which organisms better adapted to their environment survive, reproduce and pass on their advantageous alleles.

List the five stages of natural selection.

Variation exists in a population. Selection pressures act on it. Best-adapted individuals survive and reproduce . Advantageous alleles are passed on . These alleles become more frequent .

What is meant by a heritable characteristic?

One that can be inherited by, or passed on to, the next generation. It is determined by the alleles of genes an individual carries.

Give three sources of variation in a population.

Mutation . Meiosis . Random fertilisation during sexual reproduction.

Why can natural selection only occur if variation is present?

Selection acts by favouring some variants over others. Without variation, there are no differences for it to act on.

Explain natural selection using brown and white rabbits.

Predators are a selection pressure ; brown rabbits are better camouflaged . They survive and reproduce more, so the frequency of the brown fur allele increases over generations.

Why are acquired (non-heritable) characteristics not passed on?

They are gained during an organism's lifetime , not coded by alleles. So they cannot be inherited by offspring.

What happens to unfavourable characteristics over time?

Individuals with them are less likely to survive and reproduce . So the alleles decrease in frequency and may be lost from the population.

Environmental factors that affect survival chances, such as predation, act as pressures.

Environmental factors that affect survival chances, such as predation, act as selection pressures.

True or False? Organisms evolve deliberately in order to survive their environment.

False. Evolution acts on random variation — it is not a purposeful response; avoid saying it happens 'so that' an organism can survive.

Speciation is the development of new species from pre-existing species over time.

Gene flow is the exchange of genes (alleles) between populations through interbreeding.

What must happen to two populations for speciation to occur?

They must become isolated so there is no gene flow between them.

Define allopatric speciation .

Allopatric speciation is speciation caused by geographical isolation of two populations.

Define sympatric speciation .

Sympatric speciation is speciation with no geographical barrier , caused by changes that stop individuals interbreeding.

Describe how allopatric speciation occurs.

A geographical barrier separates two populations, stopping gene flow. Different selection pressures change each gene pool until they can no longer interbreed.

Give three types of change that can cause sympatric speciation.

Seasonal changes (different mating or flowering times). Mechanical changes (mismatched reproductive parts). Behavioural changes (different courtship).

How do changing allele frequencies lead to two separate species?

Different alleles become advantageous and more frequent in each population. Eventually the populations differ so much they can no longer produce fertile offspring .

Besides selection, what other process can change allele frequencies in isolated populations?

Genetic drift — the accumulation of random changes in allele frequency.

Speciation caused by a geographical barrier is called speciation.

Speciation caused by a geographical barrier is called allopatric speciation.

True or False? Sympatric speciation requires a physical barrier between populations.

False. Sympatric speciation occurs with no geographical barrier — isolation comes from changes preventing interbreeding.

Which type of speciation is the most common?

Allopatric speciation (from geographical isolation).

Give three types of evidence for evolution.

The fossil record . Real-life observations such as antibiotic resistance . Molecular evidence from DNA and proteins.

How does the fossil record provide evidence for evolution?

It shows organisms have changed over millions of years . Transitional species show how one species could evolve into another.

How is antibiotic resistance evidence for evolution by natural selection?

The antibiotic is a selection pressure . Resistant bacteria survive, reproduce and pass on the resistance allele, which increases in frequency.

How does molecular evidence support common ancestry?

Similar DNA and protein sequences are found across species. This indicates they descended from a common ancestor .

How can the similarity of gene sequences show how long ago two species diverged?

Very similar sequences suggest a recent divergence. Very different sequences suggest they diverged long ago.

Genomics is the study of the DNA base sequences of genes and genomes.

Why can protein (amino acid) sequences be used like DNA to study evolution?

The amino acid sequence is determined by the DNA base sequence of the gene. So similarities in proteins also reveal evolutionary relationships.

Peer review is the checking of a scientific study by a panel of experts before publication, to ensure the methods and analysis are valid.

How does the scientific community validate a theory such as evolution?

Studies are peer-reviewed and published, then read and critiqued by many experts. They can be repeated to check the results are reliable.

Why does peer review and repetition give us confidence in accepted theories?

They have been rigorously tested and checked by independent experts. Flawed studies can be questioned or withdrawn.

Similarities in the DNA of different species indicate that they share a ancestor.

Similarities in the DNA of different species indicate that they share a common ancestor.

How do scientific conferences help validate ideas?

Scientists present findings for questions and discussion. They can share ideas and concerns with experts from around the world.

A LevelBiologyEdexcelBiology (A) SNABFlashcards5. On the Wild SideEvolution

Evolution (Edexcel A Level Biology (A) SNAB): Flashcards

Exam code: 9BN0

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FrontEvolution by Natural Selection
Define evolution.
FrontEvolution by Natural Selection
List the five stages of natural selection.
BackEvolution by Natural Selection
Variation exists in a population.
Selection pressures act on it.
Best-adapted individuals survive and reproduce.
Advantageous alleles are passed on.
These alleles become more frequent.

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Cards in this collection (36)

Define evolution.
Evolution is a change in the heritable characteristics of organisms over generations.
Define natural selection.
Natural selection is the process by which organisms better adapted to their environment survive, reproduce and pass on their advantageous alleles.
List the five stages of natural selection.
1. Variation exists in a population.
1. Selection pressures act on it.
1. Best-adapted individuals survive and reproduce.
1. Advantageous alleles are passed on.
1. These alleles become more frequent.
What is meant by a heritable characteristic?
One that can be inherited by, or passed on to, the next generation.
It is determined by the alleles of genes an individual carries.
Give three sources of variation in a population.
Mutation.
Meiosis.
Random fertilisation during sexual reproduction.
Why can natural selection only occur if variation is present?
Selection acts by favouring some variants over others.
Without variation, there are no differences for it to act on.
Explain natural selection using brown and white rabbits.
Predators are a selection pressure; brown rabbits are better camouflaged.
They survive and reproduce more, so the frequency of the brown fur allele increases over generations.
Why are acquired (non-heritable) characteristics not passed on?
They are gained during an organism's lifetime, not coded by alleles.
So they cannot be inherited by offspring.
What happens to unfavourable characteristics over time?
Individuals with them are less likely to survive and reproduce.
So the alleles decrease in frequency and may be lost from the population.
Environmental factors that affect survival chances, such as predation, act as pressures.
Environmental factors that affect survival chances, such as predation, act as selection pressures.
True or False?
Organisms evolve deliberately in order to survive their environment.
False.
Evolution acts on random variation — it is not a purposeful response; avoid saying it happens 'so that' an organism can survive.
What is the original source of the new alleles that natural selection acts on?
Random mutation.
Define speciation.
Speciation is the development of new species from pre-existing species over time.
Define gene flow.
Gene flow is the exchange of genes (alleles) between populations through interbreeding.
What must happen to two populations for speciation to occur?
They must become isolated so there is no gene flow between them.
Define allopatric speciation.
Allopatric speciation is speciation caused by geographical isolation of two populations.
Define sympatric speciation.
Sympatric speciation is speciation with no geographical barrier, caused by changes that stop individuals interbreeding.
Describe how allopatric speciation occurs.
A geographical barrier separates two populations, stopping gene flow.
Different selection pressures change each gene pool until they can no longer interbreed.
Give three types of change that can cause sympatric speciation.
Seasonal changes (different mating or flowering times).
Mechanical changes (mismatched reproductive parts).
Behavioural changes (different courtship).
How do changing allele frequencies lead to two separate species?
Different alleles become advantageous and more frequent in each population.
Eventually the populations differ so much they can no longer produce fertile offspring.
Besides selection, what other process can change allele frequencies in isolated populations?
Genetic drift — the accumulation of random changes in allele frequency.
Speciation caused by a geographical barrier is called speciation.
Speciation caused by a geographical barrier is called allopatric speciation.
True or False?
Sympatric speciation requires a physical barrier between populations.
False.
Sympatric speciation occurs with no geographical barrier — isolation comes from changes preventing interbreeding.
Which type of speciation is the most common?
Allopatric speciation (from geographical isolation).
Give three types of evidence for evolution.
The fossil record.
Real-life observations such as antibiotic resistance.
Molecular evidence from DNA and proteins.
How does the fossil record provide evidence for evolution?
It shows organisms have changed over millions of years.
Transitional species show how one species could evolve into another.
How is antibiotic resistance evidence for evolution by natural selection?
The antibiotic is a selection pressure.
Resistant bacteria survive, reproduce and pass on the resistance allele, which increases in frequency.
How does molecular evidence support common ancestry?
Similar DNA and protein sequences are found across species.
This indicates they descended from a common ancestor.
How can the similarity of gene sequences show how long ago two species diverged?
Very similar sequences suggest a recent divergence.
Very different sequences suggest they diverged long ago.
Define genomics.
Genomics is the study of the DNA base sequences of genes and genomes.
Why can protein (amino acid) sequences be used like DNA to study evolution?
The amino acid sequence is determined by the DNA base sequence of the gene.
So similarities in proteins also reveal evolutionary relationships.
Define peer review.
Peer review is the checking of a scientific study by a panel of experts before publication, to ensure the methods and analysis are valid.
How does the scientific community validate a theory such as evolution?
Studies are peer-reviewed and published, then read and critiqued by many experts.
They can be repeated to check the results are reliable.
Why does peer review and repetition give us confidence in accepted theories?
They have been rigorously tested and checked by independent experts.
Flawed studies can be questioned or withdrawn.
Similarities in the DNA of different species indicate that they share a ancestor.
Similarities in the DNA of different species indicate that they share a common ancestor.
How do scientific conferences help validate ideas?
Scientists present findings for questions and discussion.
They can share ideas and concerns with experts from around the world.

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