MODERN EVOLUTIONARY THEORYWHAT HAPPENED AFTER DARWIN?

PROBLEMS WITH DARWIN’S THEORY

1. Why is there variation within a species?

2. How are traits passed from one generation to another?

http://4.bp.blogspot.com/-EmedhzGoq4U/Tl14PpYybRI/AAAAAAAAgT0/nzHhIdibNw8/s800/101%2Bdalmatians%2Bposter.jpg

WATSON AND CRICK’S MODEL OF DNA STRUCTURE

• genes – portions of the DNA that code for a specific protein

• proteins – amino acid sequences that are workhorses of living systems http://www.chemheritage.org/Images/Main-Images-2

50x290/Discover/Themes/Biomolecules/watson-crick1.jpg

Central Dogma of Molecular Biology

DNA RNA protein

DISCOVERY OF THE GENETIC CODE

series of instructions that shows how proteins are made based on DNA/RNA

http://4.bp.blogspot.com/-v3WGNk-6Pps/TxgT9DFFntI/AAAAAAAAGgA/U2ZMO0-Qzjc/s1600/Dna%2Bgenetic%2Bcode%2BUnseen%2BRare.jpg

SOURCES OF INHERITABLE VARIATION

http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/MUT/Mut.Mutation.html, http://static.ddmcdn.com/gif/evolution-fly.gif

1. Mutation• any change in DNA sequence• due to

• mistakes in DNA replication• environmental factors

SOURCES OF INHERITABLE VARIATION

http://1.bp.blogspot.com/_bAYLalavZ6w/TPtJ5s9xlZI/AAAAAAAAAD0/6KPTjLGRM8g/s1600/meiosis.gif

, http://local.brookings.k12.sd.us/biology/Mitosis.htm

2. Gene shuffling• independent chromosome

movement during gamete formation (223~8.4 million gene combinations)

• sexual reproduction causes variation within populations

• members of a population interbreed and are acted on in similar ways by the environment; they evolve together

EVOLUTION AS GENETIC CHANGE

Natural selection on single-gene traits

Change in allele

frequencyEvolution

http://www.brainbeau.com/cihs/Evolution/Genes_Variation_Genetic_Change_files/slide0066_image020.jpg

EVOLUTION AS GENETIC CHANGE

Natural selection

on polygenic

traits

Change in distribution

of phenotypes

Evolution

http://www.citruscollege.edu/lc/archive/biology/PublishingImages/0306l.jpg

EVOLUTION AS GENETIC CHANGE

• Natural selection is NOT always necessary for genetic change to occur

• Genetic drift• when an allele becomes common in a population by chance• not all characteristics of an organism contribute to its fitness

http://biology.unm.edu/ccouncil/Biology_203/Images/PopGen/bottleneck.gif

SPECIATIONFormation of a new species

• species group of organisms that interbreed and produce fertile offspring

• reproductive isolation• behavioral isolation• geographic isolation• temporal isolation

Evolution

Reproductive isolation

Separation of gene pools

Different responses to

natural selection

and genetic drift

http://csmith1974.files.wordpress.com/2010/11/behavioral-isolation-1.jpg, http://bioweb.cs.earlham.edu/9-12/formation/IMAGES/fish.jpg, http://biology-forums.com/gallery/33_14_07_11_5_59_19.jpeg

EXPERIMENTAL EVOLUTIONDarwin’s Hypothesis

http://4.bp.blogspot.com/-KhUhy5HCFNk/TVb-KjAZtGI/AAAAAAAAAew/f4iTxy9qSE4/s1600/Galapagos-finches.jpg

EXPERIMENTAL EVOLUTIONGrant Experiment

Enough inheritable variation in beak size and

shape

Identify and measure as many birds as possible on

one island

Many of the characteristics appeared

in bell-shaped distributions

There is great variation of inheritable traits among

finches

Differences in beak size and shape differences in

fitness

Observe survival of different birds when resources are

scarce

Birds with differently-sized beaks had different

chances of surviving a drought

Big-beaked birds had higher chances of surviving

during a drought

SPECIATION IN DARWIN’S FINCHES

Founders arrive

Separation of populations on different

islands

Natural selection changes in

the gene pool

Reproductive isolation

Ecological competition

Continued evolution

MACROEVOLUTIONLarge-scale evolutionary changes that occur over long periods of time

MASS EXTINCTIONS

• Disappearances of huge numbers of species

• Asteroids, geological activity

• Disappearance of dominant species allowed other species to take over

ADAPTIVE RADIATION

• A single group of species evolved into different forms that live in different ways

• Produces great diversity

http://mindblowingscience.com/science-by-numbers/the-5-major-mass-extinction-events/

MACROEVOLUTIONLarge-scale evolutionary changes that occur over long periods of time

CONVERGENT EVOLUTION

• Unrelated organisms resemble one another

• Due to similar environmental conditions

COEVOLUTION

• When organisms that interact closely with one another evolve together

http://students.washington.edu/kjbyers/coursework.html

MACROEVOLUTIONLarge-scale evolutionary changes that occur over long periods of time

PUNCTUATED EQUILIBRIUM

• Rapid evolution may occur after long stable periods

• Usually occurs because of genetic drift or together with adaptive radiation

CHANGES IN DEVELOPMENTAL GENES• Similar hox genes are

present in diverse organisms

• These dictate the basic body plan of the organism

• Major evolutionary changes may have occurred through these genes

http://withfriendship.com/images/i/42351/Punctuated-equilibrium-picture.jpg, http://sciphu.files.wordpress.com/2008/02/punctuated-equilibrium.jpg