Evolution and speciation

The **change in the heritable characteristics of a population over generations** (a change in allele frequency).

**Heritable**, **population**, and **over generations**.

**Allele frequency** in the **gene pool** of a population.

One particular **version of a gene** (e.g. a dark or a light allele for fur colour).

How **common** a particular allele is in the gene pool (its proportion).

All the **alleles** present in a whole **population**.

**No** — evolution happens to a **population over generations**, not to one organism.

Only **genetic** features can be **passed to offspring** — learned or lifestyle changes are not inherited.

All the members of **one species** in an area that can **interbreed**.

**No** — it is a **non-heritable** change in **one individual** within its lifetime.

**Yes** — it is a heritable change in **allele frequency** of a **population over generations**.

Across **many generations** — not within a single lifetime.

Structures with the **same basic plan but different functions**, inherited from a **common ancestor** (e.g. human arm, bat wing, whale flipper).

Structures with a **similar function but a different basic plan** and no recent shared ancestor for that feature (e.g. bird wing vs insect wing).

One ancestral form gives rise to **several different forms** — it produces **homologous** structures.

Unrelated species under similar conditions evolve **similar features independently** — it produces **analogous** structures.

**DNA / base-sequence comparison** — more shared sequence means more closely related species.

**Homologous structures, fossils, biogeography, selective breeding and DNA base sequences.**

**Divergent** evolution — one common ancestor, then modified for different jobs.

**Convergent** evolution — similar features evolved separately under the same selection pressure.

It shows that **heritable characteristics of a population can change** quickly when there is selection — here, by humans.

Traits **gained during an organism's life are not heritable**, so they cannot be passed on; evolution acts only on heritable variation.

Homologous = **same plan, different job** (common ancestor); analogous = **same job, different plan** (convergent).

DNA is an **independent** clue — when a DNA cladogram agrees with one built from anatomy, two separate lines of evidence point to the same ancestry.

Trace both branches **back to the node where they meet**; the pair that join at the **most recent (lowest) node** share a common ancestor most recently, so they are the **most closely related**.

The **most recent common ancestor** of all the species above that point.

**Mutation**, **meiosis** and **sexual reproduction**.

**Mutation** — a random change to DNA. (Meiosis and sexual reproduction only make new combinations.)

The process where individuals **best suited to the environment survive and reproduce more**, passing on their alleles.

A **change in the heritable characteristics (allele frequencies)** of a population over many generations.

Only **gene-based (allele)** variation can be **passed to offspring**; traits gained during life are not inherited.

An **inherited feature** that makes an organism **better suited to its environment**.

A **favourable allele becomes more common** in the population over generations.

**No** — the variation is **already present** (mostly from past mutations); the environment only **selects** it.

More offspring are produced than can survive, so individuals **compete** — the best-suited ones win out and reproduce.

A few bacteria already carry a **resistance allele** (mutation); the antibiotic kills the rest; survivors **reproduce** and the allele becomes **more common**.

Some individuals **survive and reproduce more than others** because of their heritable features.

How **common a particular allele is** in a population.

A group of organisms that can **interbreed and produce fertile offspring**.

The formation of a **new species** from an existing one.

When two populations can **no longer interbreed** to produce fertile offspring.

The movement of **alleles between populations** through interbreeding.

Separation of populations by a **physical barrier** (river, mountain or ocean).

They can mate, but their offspring (a **mule**) is **sterile** — so they fail the 'fertile offspring' test.

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.

(1) Populations become **reproductively isolated**; (2) they **diverge** by mutation and natural selection.

It **stops gene flow** between the two populations, allowing their gene pools to diverge.

**Mutation** (new alleles) and **natural selection** (different alleles favoured in each environment).

When they have diverged so much that they can **no longer interbreed to produce fertile offspring**.

All the **alleles present in a population**.

Divergence takes **many generations** of mutation and natural selection before interbreeding becomes impossible.

The **formation of a new species** from an existing one.

The **rapid evolution of many new species** from a single ancestor, each adapted to a **different niche**.

The particular **role and way of life** of a species — what it eats, where it lives and how it behaves.

Reaching **new, empty habitats** (for example a fresh island chain) with many unfilled niches.

A **sharp rise in the number of species** in one group over a relatively short time.

Speciation by the **slow build-up of small heritable changes** over a long time.

Speciation that happens **suddenly**, over a short time (for example by a **chromosome-number change**).

A **smooth series of in-between forms**, each only slightly different from the one before.

A **change in chromosome number**, which instantly stops the plant breeding with its parent population.

**Yes** — adaptive radiation, gradual and abrupt speciation all rely on **natural selection** and **reproductive isolation**.

One group **becoming more varied** — splitting into **many** different species over time.