Evolution (Cambridge (CIE) A Level Biology): Flashcards
Exam code: 9700
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- FrontTheory of Evolution
Define evolution.
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Cards in this collection (14)
Define evolution.
Evolution is the change in the allele frequencies (gene pool) of a population over many generations, which can lead to the formation of new species.
Define gene pool.
A gene pool is all the alleles of all the genes present in a population at a given time.
Outline the theory of evolution.
New species form from pre-existing species over time.
This happens as a result of changes to gene pools from generation to generation, driven by natural selection.
All the alleles present in a population at one time make up its .
All the alleles present in a population at one time make up its gene pool.
How can DNA sequence data show evolutionary relationships between species?
The more similar the base sequences of two species' DNA, the more closely related they are.
They also shared a common ancestor more recently.
Why is comparing DNA sequences more reliable than comparing physical features?
It directly compares the genetic material.
Closely related species have accumulated fewer differences by mutation, giving objective evidence of relatedness.
True or False?
Two species with very similar DNA base sequences are likely to be closely related.
True.
Fewer differences in base sequence indicate a more recent common ancestor.
Define speciation.
Speciation is the formation of a new species from pre-existing species, occurring when populations become reproductively (genetically) isolated.
Define allopatric speciation.
Allopatric speciation is speciation caused by the geographical separation of populations (e.g. by a river, mountain or ocean).
Define sympatric speciation.
Sympatric speciation occurs without geographical separation, due to ecological or behavioural isolation within the same area.
Outline how allopatric speciation occurs.
Step 1: A physical barrier geographically separates two populations.
Step 2: Gene flow between them stops.
Step 3: Different selection pressures, mutations and drift change each gene pool differently.
Step 4: The populations can no longer interbreed to produce fertile offspring — they are separate species.
Give two types of isolation that can cause sympatric speciation.
Ecological isolation — occupying different habitats or niches.
Behavioural isolation — different courtship behaviours or breeding times.
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 geographical barrier.
False.
That describes allopatric speciation; sympatric speciation occurs without geographical separation.
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