Warm-Up #39• Answer questions #1-4 on Text page

372 Section Assessment.

• Answer questions #1-4 on Text 377 Section Assessment

Voyage of the Beagle (1839 - 1844)

• Darwin’s Voyage - During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time.

Galapagos Islands• During his travels Darwin was amazed how different

organisms were so well adapted to many different environments.

• He saw patterns of diversity • Not just in living organisms, but also in fossil records.• The Galapagos Islands were a microcosm of Evolution

Vocab• Evolution - change in

a kind of organism over time; process by which modern organisms have descended from ancient organisms

• Theory - well-tested explanation that unifies a broad range of observations

Questions1. Key Concept What two ideas from

geology were important to Darwin’s thinking?

2. Key Concept According to Lamarck, how did organisms acquire traits?

3. Key Concept According to Malthus, what factors limited population growth?

4. Why has Lamarck’s theory of evolution been rejected?

Idea’s that shaped Darwin’s Thinking1. James Hutton and Charles Lyell helped

scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.

2. Jean-Baptiste Lamarck 1809 - proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species

3. Thomas Malthus (English Economist) - reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone.

Lamarck (His theory is wrong)1. Tendency Toward Perfection

1. Innate tendency toward complexity and perfection1. Birds acquired the urge to fly

1. Kept trying to fly

2. Use and Disuse1. Using a trait (wings) causes them to

become stronger and larger2. Disuse causes it to disappear

3. Inheritance of Acquired Traits1. Passing acquired traits from one

generation to the next

Lamarck

Daily Quiz #261. Define evolution.

2. Define natural selection.

3. What are structures that have different mature forms, but develop from the same embryonic tissue called?

Evolution

Charles Darwin and Natural Selection

Two things to know before talking about

Natural Selection

• In our world there is:

• Natural Variation - differences among individuals of a species

• And in order to understand Natural Selection you need

to understand

• Artificial selection - selection by humans for breeding of useful traits from the natural variation among different organisms

Vocab• struggle for existence - competition

among members of a species for food, living space, and the other necessities of life

• Fitness - ability of an organism to survive and reproduce in its environment

• Adaptation - inherited characteristic that increases an organism’s chance of survival (increases an organism’s fitness)

• survival of the fittest - process by which individuals that are better suited to their environment survive and reproduce most successfully; also called natural selection

Natural Selection• is the process by which individuals

that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest

• In order for natural selection to occur there must be:• Natural Variation

• Struggle for existence

• An adaptation that increases the fitness of one organism over another

Descent With Modification• Darwin’s proposed that

over long periods natural selection produces organisms that:• Have different

structures• Establish different

niches• Or occupy different

habitats

• As a result species have descended, with changes from other species over time.

• Darwin’s principle of Descent with modification

Evidence of Evolution

Evidence of Evolution

Fossil RecordHomologous

Body Structures

Early Development

Geographic Dist. Of Species

PhysicalRemains

Common Ancestors

SimilarGenes

SimilarGenes

Composed of Which

IndicatesWhichImplies

WhichImplies

The Fossil Record

Geographic Distribution of Living Species

• Darwin’s Finches—descended from a common ancestor on South American mainland—each species adapted to its specific environment.

• Similar environments on different continents can lead to different species evolving some common features even though they descend from different ancestors. (beaver and capybara)

Darwin’s Finches

Geographical Distrib. of Species

Common Descent

Homologous and Analogous StructuresAnalogous

• 1.Different ancestors• 2.“analogy”=like• 3.Different

underlying structures

• 4.Same Function• 5.Similar

Environments

Homologous

• 1.Same ancestor• 2.“homo”=same• 3.Same underlying

structures• 4.Different Functions• 5.Different

Environments

Homologous and Analogous

Vestigial Structure• Structures or Organs that serve no

purpose or function.

Embryological Similarities• Many embryos of vertebrates look

especially similar during early stages of development.

• Same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.

• These features develop into homologous structures.

• Figure 15-17

Similarities in early development

Comparative Biochemistry

Similar DNA sequences=

Similar Gene segments of the DNA

• Code for similar traits

• In closely related species

• Amino Acid Lab Today

Plate Tectonics

• Geological theory:• Continental masses were one land

mass that explains• Closely related species have common

ancestors on now separated continents

Summary of Darwin’s Theory1. There is variation (genetic…)between organisms which can be

inherited.2. Organisms in nature produce more offspring than can survive,

and many of those that survive do not reproduce.3. Because more organisms are produced than can survive, members

of each species must compete for limited resources.4. Because each organism is unique, each has different advantages

and disadvantages in the struggle for existence.5. Individuals best suited to their environment survive and

reproduce most successfully. The characteristics that make them best suited to their environment are passed on to offspring. Individuals whose characteristics are not as well suited to their environment die or leave fewer offspring.

6. Species change over time. Over long periods, natural selection causes changes in the characteristics of a species, such as in size and form. New species arise, and other species disappear.

7. Species alive today have descended with modifications from species that lived in the past.

8. All organisms on Earth are united into a single tree of life by common descent.

Amino Acid Sequencing Lab

Homework—Due Friday 1/14• Complete Amino Acid Sequencing

Lab

• Read Text Page 392-410

• Study Guide 111-112

Warm-Up #40• Compare your answers on the Amino

Acid lab with your partner’s answers.

• Write a conclusion that summarizes how Biochemical Evidence provides support for evolution.

Daily Quiz #27• The number of times that a specific

allele occurs in a gene pool compared to other alleles is called what?

• What is gene shuffling?

• How many phenotypes result from single-gene traits?

Chapter 16

GENES

and VARIATION

Darwin’s Ideas Revisited

• Darwin’s ideas had to be integrated with our new found information on Genetics.

Genes and Variation

• Gene Pools - combined genetic information of all the members of a particular population

• Relative Frequency - number of times an allele occurs in a gene pool compared with the number of times other alleles occur

Genes and Variation• There are two main sources of genetic

variation:• Mutations –

• What are the two main types of mutations?

• Gene shuffling –• When and how does gene shuffling occur?

•Big question: Do mutations and gene shuffling cause evolution? In other words do mutations and gene shuffling change the relative frequencies of alleles in a gene pool?

Genes and Variation• single-gene trait - trait controlled by a

single gene• How many phen-otypes areproduced?

Genes and Variation• polygenic trait - trait controlled by two

or more genes• How many pheno-types are produced?

Genetic Change (Evolution)Big Question

Since mutations and gene shuffling does not change the relative frequencies of alleles in a population, what causes the change of allele frequencies in a population?

Natural Selection

Single-gene Trait (Natural Sel.)

Natural selection on single-gene traits can lead to changes in allele frequencies and, thus, to evolution.

Polygenic Traits (Natural Sel.)

• Natural selection can affect the distributions of phenotypes in any of three ways:

•directional selection – form of natural selection in which the entire curve moves; occurs when individuals at one end of a distribution curve have higher fitness than individuals in the middle or at the other end of the curve

•stabilizing selection - form of natural selection by which the center of the curve remains in its current position; occurs when individuals near the center of a distribution curve have higher fitness than individuals at either end

•disruptive selection - form of natural selection in which a single curve splits into two; occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle

Directional Selection

Stabilizing SelectionStabilizing

selection takes place when

individuals near the center of a curve have higher fitness than individuals at either end. This example shows that human babies born at an average weight are more likely to survive than babies born either much smaller or much larger than average.

Disruptive Selection

• What will Disruptive Selection result in?

Peppered Moths Lab• Microevolution of a moth population

in England in response to a change in environment.

• http://wn.com/Peppered_moth_evolution

Homework—Due Tuesday 1/18• Read Text 397-402 and 435-440

• Complete Study Guide 113-114

Genetic Drift• Genetic Drift - random change in allele

frequencies that occurs in small populations

• In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. Over time, a series of chance occurrences of this type can cause an allele to become common in a population.

• founder effect - change in allele frequencies as a result of the migration of a small subgroup of a population

Genetic Drift and Founder Effect

Does Evolution occur all of the time?

NO

Hardy-Weinberg principle• The principle that allele frequencies

in a population will remain constant unless one or more factors cause the frequencies to change

If there are no factors causing allele frequencies to change then the population is in……..

• genetic equilibrium - situation in which allele frequencies remain constant

Genetic Equilibrium• Five conditions are required to

maintain genetic equilibrium from generation to generation: • random mating• the population must be very large• there can be no movement into or out of

the population• no mutations (that filter into the gene

pool)• no natural selection

Homework • Studyguide 16-3

• Test Chapter 15 and 16 on Tuesday

1. Describe how natural selection can affect traits controlled by single genes.

2. Describe three patterns of natural selection on polygenic traits. Which one leads to two distinct phenotypes?

3. How does genetic drift lead to a change in a population’s gene pool?

4. What is the Hardy-Weinberg principle?

When evolution DOES OCCUR• The process of SPECIATION - formation of

new species• Speciation has occurred when – population have

become reproductively isolated from one another

• reproductive isolation - separation of species or populations so that they cannot interbreed and produce fertile offspring• Reproductive isolation can develop in a

variety of ways, including behavioral isolation, geographic isolation, and temporal isolation.

Behavioral Isolation• form of reproductive isolation in

which two populations have differences in courtship rituals or other types of behavior that prevent them from interbreeding

• Examples• Mating calls• Mating dances

Geographic Isolation• form of

reproductive isolation in which two populations are separated physically by geographic barriers such as rivers, mountains, or stretches of water

Temporal Isolation• form of reproductive isolation in

which two populations reproduce at different times

Speciation of Darwin’s Finches• Speciation in the Galápagos finches

occurred by the: • founding of a new population• geographic isolation• changes in the new population’s gene

pool• reproductive isolation• ecological competition