Bio. 230 --- Evolution III - PowerPoint PPT Presentation

Presentation Transcript

Bio. 230 --- Evolution III

Some History of Evolutionary Thought

Empedocles (Greek, ~490 to 430 B.C.)

1st to propose a clear concept of biological evolution

Abiogenesis

Plants arose 1st; their buds gave rise to animals

Gradual process

Some History of Evolutionary Thought

Aristotle (Greek, 384-348 B.C.), student of Plato (~427-347 B.C.)

Similar ideas

Abiogenesis

Acquired characteristics

Species could hybridize

Some History of Evolutionary Thought

Lamarck (French, 1744-1829)

1st in more modern times to put forth a comprehensive & logical evolutionary theory

Acquired characteristics

Pangenesis / pangenes

Newer forms were more complex (and “perfect”) than their ancestors

Some History of Evolutionary Thought

Charles Darwin (English, 1809-1882)

Started out as a special creationist

READ handout: “A comparison of views on variation and heredity”

1831-1836 --- voyage on the Beagle

Then worked for more than 20 years

1838 – He read AN ESSAY ON THE PRINCIPLE OF POPULATION by Thomas Malthus

Natural Selection

Some History of Evolutionary Thought

Charles Darwin (English, 1809-1882)

1844 -- Put together a brief essay (unpublished)

Early 1858 – Essay from Alfred Russel Wallace

Later 1858 – Published Wallace’s essay and excerpts from his own 1844 essay in the Journal of the Linnaean Society

1859 – published THE ORIGIN OF SPECIES BY MEANS OF NATURAL SELECTION

Darwin’s Main Points

Overproduction of offspring

Variation within a species and at least some of it is hereditary

Limits on resources; engenders a strugglefor existence

Generally the fittest survive(= Natural Selection)

Eliminating of unfavorable traits and accumulation of more favorable traitsgives rise to new forms of life

NeoDarwinism or The Modern Synthetic Theory

Darwin did not have all the answers

1937 – Theodosius Dobzhansky (Genetics and the Origin of Species) began the MST

1950s to 1970s additional seminal workC. Leo Babcock (plant evolution),Edgar Anderson (Introgressive Hybridization),EarnstMayr (animal evolution),G. L. Stebbins (plant evolution),J. Watson & F. Crick (DNA structure), M. Nirenberg & J. H. Matthaei (genetic code)

Evolutionary Potpourri

Evolution occurs in POPULATIONS*

Populations can have a change in gene / allele frequency

All populations are phenotypically polymorphic

New gene / allele combinations can come about from CROSSINGOVER and RECOMBINATION during sexual reproduction

New alleles / genes come about by some type of MUTATION

Microevolution* vs. Macroevolution*

Are the processes that drive each different?

Gradualism vs. Punctuated Equilibrium*

Are the processes that drive each different?

The Gene Pool (I)

DEFINITION* -- ALL of the genes AND alleles in a population taking into account their frequency

It is the total supply of genetic units available to form the next generation

Not possible to study the whole gene pool

Will look at a “mini” gene pool (for the gene “A”)

Only two alleles: A and a

3 possible genotypes (AA, Aa, aa)

We start a population with a certain frequency of A and a

The Gene Pool (II)

What will happen to the allele (and genotype) frequencies over the generations??????????

Solved independently in early 20th century by: George Hardy & Wilhelm Weinberg

Known by various aliases: Hardy-Weinberg Equilibrium Hardy-Weinberg Theorem Hardy-Weinberg Law

Hardy-Weinberg Equilibrium

DEFINITION* -- Given certain conditions the allele frequencies remain constant from generation to generation AND after one generation of random mating even the genotype frequencies will remain constant and can be predicted from the equation (p + q)2 = p2 + 2pq + q2

p = the frequency (f) of A q = the frequency (f) of ap2 = f AA, 2pq = f Aa, q2 = faa

Hardy-Weinberg Conditions (I)

Infinitely large PopulationEliminates chance fluctuations (genetic drift)

Random MatingMeans no inbreeding; no positive (+) or negative (-) assortative mating

No net mutationEliminates mutation pressure

No net population movementEliminates net gene flow

Hardy-Weinberg Conditions (II)

No natural selectionMeans no type is better than another; all types must survive at proportional rates

-----------------------------------------------------------------

“Survival of the Fittest” does not mean that organisms fight or that organism have to die

Death (real) vs. Genetic Death

Natural Selection works on PHENOTYPE

Genetic Drift

A change in the allele frequencies in a gene pool due to random (chance) events
More likely to happen in small populations OR when a small sample is taken from a large population
Due to random sampling in a less than infinite population