Speciation by splitting of pre-existing species
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Flip to reveal answersDefine a species (biological species concept).
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Question
Define a species (biological species concept).
Answer
A group of organisms that can **interbreed and produce fertile offspring**.
Question
Define speciation.
Answer
The formation of a **new species** from an existing one.
Question
Define reproductive isolation.
Answer
When two populations can **no longer interbreed** to produce fertile offspring.
Question
What is gene flow?
Answer
The movement of **alleles between populations** through interbreeding.
Question
What is geographic isolation?
Answer
Separation of populations by a **physical barrier** (river, mountain or ocean).
Question
Why are a horse and a donkey different species?
Answer
They can mate, but their offspring (a **mule**) is **sterile** — so they fail the 'fertile offspring' test.
Question
How would you test whether two similar forms are the same species?
Answer
Do a **breeding (crossing) test**: try to **interbreed** them and check whether the offspring are **fertile**. Fertile offspring ⇒ same species; no offspring or sterile offspring ⇒ different species.
Question
What are the two steps of speciation?
Answer
(1) Populations become **reproductively isolated**; (2) they **diverge** by mutation and natural selection.
Question
What does a geographic barrier do to gene flow?
Answer
It **stops gene flow** between the two populations, allowing their gene pools to diverge.
Question
What two processes drive the divergence?
Answer
**Mutation** (new alleles) and **natural selection** (different alleles favoured in each environment).
Question
When are two populations finally two species?
Answer
When they have diverged so much that they can **no longer interbreed to produce fertile offspring**.
Question
What is a gene pool?
Answer
All the **alleles present in a population**.
Question
Why does isolation alone not instantly make two species?
Answer
Divergence takes **many generations** of mutation and natural selection before interbreeding becomes impossible.
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Topic 1.8 hub
Evolution and speciation
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