Natural Selection & Evolution (OCR GCSE Combined Science A (Gateway): Biology): Flashcards
Exam code: J250
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How much genetic variation is there within a population?
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How much genetic variation is there within a population?
There is usually extensive genetic variation within a population of a species.
What causes genetic variation within a population?
The population contains many different alleles of its genes.
Where do the different alleles in a population originally come from?
Mutations — random changes to the DNA base sequence.
How often do mutations occur?
Continuously, but any individual mutation is rare and random.
How can a mutation change a protein?
The DNA base sequence codes for the amino acid sequence, so a change to the bases can change the protein that is built.
Why do most mutations not affect an organism?
They either leave the protein unchanged, or change it so slightly that its function is unaffected.
How can a changed protein shape stop an enzyme working?
If the active site changes shape, the substrate can no longer bind to it.
What decides whether a new allele spreads through a population?
Whether it gives the individuals that carry it an advantage or a disadvantage.
Give an example of a mutation that gives a survival advantage.
A change in a bird's feather colour that makes it more attractive to mates, so it breeds more often and passes the allele on.
Why does variation matter to the survival of a species?
It means some individuals may be better suited to a change in the environment, so the species can survive it.
Can a mutation be harmful?
Yes. A significantly altered protein can stop working properly, as in sickle cell anaemia.
Genetic variation within a population exists because there are different ＿＿＿＿＿＿＿＿ of each gene.
Genetic variation within a population exists because there are different alleles of each gene.
A mutation is a random change in the sequence of DNA ＿＿＿＿＿＿＿＿.
A mutation is a random change in the sequence of DNA bases.
True or False?
Members of the same species are genetically identical.
False.
There is usually extensive genetic variation within a population.
True or False?
Mutations only ever harm an organism.
False.
Most have no effect, and a rare few give a survival advantage.
Define natural selection.
The process by which individuals with characteristics best suited to their environment are more likely to survive and reproduce.
Define evolution.
A change in the inherited characteristics of a population over time, through natural selection.
Describe the process of natural selection.
Individuals show variation caused by mutation, and more offspring are produced than can survive.
Those best suited survive and reproduce, passing their alleles on, so those characteristics become more common.
Where does the variation that natural selection acts on come from?
Mutations, which produce new alleles in the population.
Why is there a struggle for survival within a population?
More offspring are produced than the environment can support, so individuals compete for food and other resources.
What happens to a population if its environment changes?
Natural selection may now favour different characteristics, so over generations the population changes.
How can natural selection lead to a new species forming?
Two populations may evolve until they are so different that they can no longer interbreed to produce fertile offspring.
Name the two types of evidence for evolution.
Fossils and antibiotic resistance in bacteria.
Define fossil.
The preserved remains or traces of an organism, such as bones, footprints or burrows.
How do fossils provide evidence for evolution?
They can be dated and placed in a sequence.
This shows how organisms have gradually changed over millions of years, from simple to more complex forms.
Explain how antibiotic resistance arises in bacteria.
A chance mutation makes some bacteria resistant, so they survive treatment while the rest die.
They reproduce with less competition, so the resistance allele spreads through the population.
Why is antibiotic resistance such useful evidence for evolution?
Bacteria reproduce roughly every 20 minutes, so evolution can be observed within a short time.
Why is antibiotic resistance a problem for medicine?
Diseases that were once controlled by antibiotics may become untreatable.
Individuals best suited to their environment are more likely to survive and ＿＿＿＿＿＿＿＿.
Individuals best suited to their environment are more likely to survive and reproduce.
Evolution is a change in the inherited characteristics of a ＿＿＿＿＿＿＿＿ over time.
Evolution is a change in the inherited characteristics of a population over time.
True or False?
Individual organisms evolve during their lifetime.
False.
It is the population that evolves, over many generations, as allele frequencies change.
True or False?
Bacteria become resistant because antibiotics are used.
False.
Resistance arises from a chance mutation. Using antibiotics only selects for the bacteria that already have it.
Define classification.
Sorting organisms into groups based on the similarities and differences between them.
Name the two types of classification system.
Artificial and natural classification.
Define artificial classification.
Grouping organisms by observable features that are not related to evolution, such as whether they lay eggs.
Define natural classification.
Grouping organisms by their evolutionary relationships, using common ancestors and shared structural features.
Give one use of artificial classification today.
Ecological keys, which group organisms in a way that makes them easy to identify.
Why is natural classification preferred by scientists?
It reflects how organisms are actually related through evolution, rather than just how they look.
What were organisms originally classified by?
Their morphology — overall form and shape — and their anatomy, the detailed body structure.
Which developments have changed how organisms are classified?
The microscope, knowledge of biochemistry, and above all DNA sequencing.
Define molecular phylogenetics.
Classifying organisms by comparing their DNA base sequences to work out how closely related they are.
What does a similar DNA base sequence tell you about two species?
The more similar their DNA, the more closely related they are, and the more recent their common ancestor.
Two species differ by one DNA base; a third differs by twenty. Explain.
The first two are more closely related, because fewer changes have built up since they shared a common ancestor.
Why can amino acid sequences also be used to classify organisms?
DNA codes for amino acid sequences, so similar proteins point to similar DNA and a closer relationship.
＿＿＿＿＿＿＿＿ classification groups organisms by their evolutionary relationships.
Natural classification groups organisms by their evolutionary relationships.
Classifying species by comparing their DNA is called molecular ＿＿＿＿＿＿＿＿.
Classifying species by comparing their DNA is called molecular phylogenetics.
True or False?
Organisms that look alike must be closely related.
False.
Appearance can be misleading, which is why DNA sequencing gives a far more reliable answer.
True or False?
DNA sequencing has changed how organisms are classified.
True.
It allows classification by how closely related species really are, rather than by appearance alone.
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