Some of the slides (35-45) we didn’t go over during the last class will be part of today’s lecture.

Ch. 17 Microevolution

• The smallest unit that evolves is a population:– all the members of a single species living in a

defined geographical area at a given time.

originalcoloration

(a) Original environment

(b) Altered environment

lightercoloration

expanse ofbarren terrain

darkercoloration

population A

population B

Figure 17.1

Genetic Basis of Evolution

• Genes exist in variant forms called alleles– Different versions of the same gene– Usually an individual only has 2 different alleles

of the same gene• One from bio mom, one from bio dad

Genetic Basis of Evolution

• A population, however, is likely to possess many alleles for a given gene. – gene pool: The sum total of alleles in a

population

• The basis of evolution is a change in the frequency of alleles in a gene pool.

Alternative Versions:Real Life Example

Underwear

17.2 Evolution as a Change in the Frequency of Alleles

Figure 17.2

maternalchromosome 3

paternalchromosome 3

maternalchromosome 3

paternalchromosome 3

allelesalleles

dark coloration light coloration

a1 a2 a2 a4

Genetic Basis of Evolution

• With such a change, a population can be said to have evolved.

• Evolution at this level is referred to as microevolution: a change of allele frequencies within a population over a relatively short period of time.

Genetic Basis of Evolution

• Conversely, macroevolution, a product of microevolution, is evolution on a larger scale.

• Macroevolution is evolution that results in the formation of new species or other large groupings of living things.

17.3 Five Agents of Microevolution

• Five evolutionary forces can result in changes in allele frequencies within a population.

• These agents of microevolution are:1. mutation2. gene flow3. genetic drift4. sexual selection5. natural selection

Agents of Change: Five Forces That Can Bring about Change in Allele Frequenciesin a Population

Agent Description

Mutation

Gene flow

Genetic drift

Sexual selection

Natural selection

Alteration in an organism’s DNA; generally has no effect or a harmful effect. But beneficialor “adaptive” mutations are indispensable to evolution.

The movement of alleles from one population to another. Occurs when individuals movebetween populations or when one population of a species joins another, assuming thesecond population has different allele frequencies than the first.

Chance alteration of gene frequencies in a population. Most strongly affects smallpopulations. Can occur when populations are reduced to small numbers (the bottleneckeffect) or when a few individuals from a population migrate to a new, isolated locationand start a new population (the founder effect).

Occurs when some members of a population mate more often than other members.

Some individuals will be more successful than others in surviving and hence reproducing,owing to traits that give them a better “fit” with their environment. The alleles of thosewho reproduce more will increase in frequency in a population.

Table 17.1

1. Mutations

Figure 17.3

Normal Point mutation

incorrectnucleotide sequence

correctnucleotide sequence

Normal Deletion

completechromosome 5

incompletechromosome 5

(a) (b)

• Any permanent alteration in an organism’s DNA• Some are heritable - they can be passed on from one

generation to the next

Mutations

• Happens fairly infrequently– most mutations either have no effect or are harmful

• Adaptive mutations – Vital to evolution – The only way entirely new genetic information

comes along

2. Gene Flow

• The movement of genes from one population to another.

• Takes place through migration– the movement of individuals from one

population into the territory of another

Figure 17.4

(a) Hawaiian silversword (b) Tarweeds in California

North America

HawaiianIslands Pacific

Ocean

gene

flow

How did plant life come about in Hawaii?

Genetic Drift

• A random change in allele frequency• Not related to reproductive success

Genetic Drift

Figure 17.5

Genetic Drift

• Genetic drift can have large effects on small populations through two common scenarios:– the Bottleneck Effect– the Founder Effect

4. Sexual Selection – the guys with more game get more ladies

• A form of natural selection that can affect the frequency of alleles in a gene pool

• Occurs when differences in reproductive success arise because of differential success in mating– Mate more, pass more genes along

Sexual Selection

Figure 17.7

• If you got more game than the other guys, you pass along more of your genes

• This will increase the frequency of your alleles the next generation of the population

5. Natural Selection

• Most powerful force • In a population, if you are more likely to

survive, you are more likely to reproduce and pass on traits that allowed you to survive

© 2011 Pearson Education, Inc.

Ch. 18 The Outcomes of Evolution – Macroevolution

18.1 What is a species?

Biological Species Concept

Species: different kinds of organisms

Species are natural populations of organisms that:• Interbreed with each other or could

possibly interbreed in a natural environment

• Cannot interbreed with organisms outside their own group (reproductive isolation)

What Is a Species?

• Definition does not fit all– Only sexually reproducing organisms

• Bacteria & archaea -reproduce through simple cell division

18.2 How Do New Species Arise?

• Allopatric Speciation• Sympatric Speciation

18.4 The Categorization of Earth’s Living Things

How do we name species?

We need an organizational system!

Carolus Linnaeus…

Carolus Linnaeus and Binomial Nomenclature

A scientific name consists of two parts:1. Genus2. Species

Horse: Equus ferusZebra: Equus quagga

Taxonomy

• More than just two names…• 8 major categories (from least to most

inclusive)– species, genus, family, order, class, phylum,

kingdom, and domain

Linnaean System of Classification

Domain

Kingdom

Phylum

Class

Order

Genus

You should know the order

Species

Did King Phillip Come Over For Good Sex?

Family

Figure 18.10

Linnaean System of Classification

Kingdom(Animalia)

Phylum(Chordata)

Class(Mammalia)

Order(Carnivora)

Family(Felidae)

Genus(Felis)

Species(Felisdomestica)

Present dogs raccoons bearssea

lions seals walrus weasels

10

30

20

40

50

60

ancestralcarnivores

Mil

lio

ns

of

year

s ag

o

Figure 18.11

Family Tree of

MammalianCarnivores

Systematics

• A type of biology that looks at how closely organisms are related– Think family tree

• You are more closely related if you share a mom than if you just share a grandma

• Evolutionary family trees = “phylogenies”– Various evidence

• radiometric dating, the fossil record, DNA sequence comparisons

18.5 Classical Taxonomy and Cladistics

• In determining phylogeny, classical taxonomy establishes evolutionary relationships

• Classical taxonomy is subjective• Cladistics

– a firm rule for inferring relatedness– It counts the shared derived characters two

organisms have– Establishes lines of descent

hagfish lizard deer lion seal

aquatichabitat

carnivorousfeeding

mammaryglands

tetrapod structure

Derivedcharacters

A Simple Cladogram

Figure 18.13

(a) Classical view of relationships among tetrapods (b) Cladistic view of relationships among tetrapodsReptilia Aves Mammalia

turt

les

snak

es

liza

rds

cro

cod

iles

din

osa

urs

bir

ds

mam

mal

s

mam

mal

s

turt

les

snak

es

liza

rds

cro

cod

iles

din

osa

urs

bir

ds

Classical Taxonomy and Cladistics

Figure 18.14

Activity

• Everyone will turn in their own paper• You may work in small groups