UNIT ____: Species and Speciation Name: ________________________

Essential Idea(s): Gene pools change over time.

IB Assessment Statements and Class Objectives

Species are groups of organisms that can potentially interbreed to produce fertile offspring (4.1.U1)

Define species according to the biological species concept.
Describe limitations of the biological species concept.

Speciation is the process by which new species are formed from a common ancestor.

Define speciation.

Speciation occurs when two populations of a species are isolated and evolve along different lines (4.1.U2).

Define population.
Define reproductive isolation.
Outline how reproductive isolation can lead to speciation.

Reproductive isolation of populations can be geographic, behavioral or temporal (10.3.U3)

Compare allopatric and sympatric speciation.
Explain temporal, behavioral and geographic isolation as mechanisms of speciation.
Describe an example of temporal, behavioral and geographic reproductive isolation.

Infertile hybrids illustrate how reproductive isolation prevents mixing of alleles between populations which have evolved differences.

Define hybrid.
State an example of an infertile hybrid.
Explain how infertile hybrids illustrate reproductive isolation between populations.

Speciation due to divergence of isolated populations can be gradual (5.1.U5 and 10.3.U4)

Describe the process of gradual speciation.

Continuous variations across the geographical range of related populations matches the concept of gradual divergence (5.1.U6).

Explain how continuous variation across geographical ranges is evidence of gradual divergence.
State an example of recognizably different populations of the same species across a geographical range.

A gene pool consists of all the genes and their different alleles presented in an interbreeding population (10.3.U1).

Define gene pool.
Define interbreeding.

Allele frequencies can change over time, leading to an overall evolutionary change (10.3.U2).

Define evolution.
Outline four factors that can cause evolutionary change.
Summarize John Endler’s experiments with guppies in Trinidad which demonstrate phenotypes undergoing evolution.

The Hardy-Weinberg theorem can be used to calculate allele frequencies in geographically isolated populations (10.3.S1).

State the Hardy-Weinberg equations.
List the conditions under which populations maintain Hardy-Weinberg equilibrium.
Given data, calculate allele frequencies of genes in a gene pool.
Use Hardy Weinberg to compare allele frequencies of two populations.
Describe how variations in the allele frequencies of a gene may be evidence of speciation.

Speciation can occur abruptly via polyploidy (10.3.U5, 10.3.A2 and 10.3.NOS).

Define polyploidy.
Outline causes of polyploidy.
Explain how polyploidy can lead to speciation.
List example species in the genus Allium (by common name).
Outline how polyploidy has led to many species of Allium.

What Is a Species?

Biological Species Concept

A species is a group of (actual or potentially)

interbreeding populations with a

common gene pool that are

reproductively isolated from other groups.

You can’t necessarily tell species just

just by outward appearance!

Example of a Single Species with

Phenotypically Different Appearances

Example of a Two Species

with Phenotypically Similar Appearances

LIMITATIONS of the Biological Species Concept:

Extinct species

Asexual Reproducing Species

Hybrids

EVOLUTION…

DEFINITION:

CAN LEAD TO SPECIATION…

DEFINITION:

Species are formed through a two-step process:

Populations become reproductively isolated from each other

Geographic Isolation

Temporal Isolation

Behavioral Isolation

Description:

Sketch Example:

Isolated populations evolve independently

Continuous variations across the geographical range

POLYPLOIDY

DEFINITION:

EXAMPLE FORMATION OF A POLYPLOID

The genus Allium includes onion, garlic, chives, scallion, shallot and leek. In many of these species of plants, polyploidy has created a large number of phenotypes and chromosome numbers. This results in a number of reproductively isolated but similar species.

Examples of polyploidy in Allium species includes:

Diploid (2n) = ~ 16 chromosomes (e.g. Allium cepa – garden onion)
Triploid (3n) = ~ 24 chromosomes (e.g. Allium carinatum – keeled garlic)
Tetraploid (4n) = ~ 32 chromosomes (e.g. Allium tuberosum – chinese chives)

GENE POOLS

When scientists determine whether a population is evolving, they may exam the population gene pool:

A= a =

Frequency of A

Frequency of a

Frequency of A

Frequency of a

Frequency of A

Frequency of a

Hardy-Weinberg Theorem

The Hardy Weinberg equations are a mathematical model used to calculate allele and/or genotype frequencies of traits with dominant and recessive alleles. The model assumes that a population:

is large
has random mating
is NOT experiencing selection
has no mutation, emigration or immigration

If these assumptions are met then the allele frequencies of the population will remain stable over time.

If the population is not in Hardy Weinberg equilibrium, it can be concluded that the population is evolving.

Calculating Allele Frequencies:

Calculating Genotype Frequencies: