Evolution Midterm I

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Lamarckian evolution

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something acquired during the life of an individual is passed on (ie giraffe's neck)

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Basic definition: Darwinian Evolution

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descent thru modification in a population by means of natural selection

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Darwin's 2 observations

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1. organisms' basic strxrs show incredible similarities, based on 'archetypes'

2. organisms display a wonderful 'fit' to environment - well adapted

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Basic definition: adaptations

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traits that have evolved by natural selection

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Transformational vs variational evolution

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Darwin brought forth idea of variation in population, not gradient-like transformational evolution

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3 conditions MUST be met for Natural Selection to occur

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1. there is VARIATION

2. the variation is HERITABLE

3. different forms vary NONRANDOMLY in reproductive success

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MODERN SYNTHESIS THEORY (NeoDarwinism) 4 things

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-mutations are random w respect to FITNESS, not directed
-Nat Sel is mechanism of adaptive evol. change
-evol. change is GRADUAL
-macroevol results from accumulation of microevol. changes

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DARWINIAN FITNESS

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avg potential genetic contribution of individ. with a specified geno or phenotype to the next generation

*depends on ENVIRONMENT*

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5 basic properties of SELECTION

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1. cannot be directional or progressive

2. there is no foresight

3. only acts on existing variation

4. doesn't perfect phenotypes

5. can lag behind environment

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PRECAMBRIAN ERA

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4.6 bill - 544 million years ago

fossils are UNICELLULAR

~all marine~

*ends with Cambrian explosion*

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3 steps for abiotic conditions -> life

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1. assemble simple molecules into complex polymers

*2. assemble these to STORE INFORMATION/catalyze rxns

3.add membranes and energy source

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RNA world hypothesis

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ribozymes and RNA: viable hypothesis bc found that there can assemble a ribozyme that forms phosphodiester bonds necessary for polymerization rxns (induce random mutations to evolve this)

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FIRST EVIDENCE FOR EUKARYOTIC CELL

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1.8 billion years ago (Precambrian)

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WHEN ACTUAL MULTICELLULAR ORGANISMS APPEAR?

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600 million years ago: Ediacaran biota; before Cambrian explosion

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THE CAMBRIAN EXPLOSION

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544 mya

massive burst in diversity: ADAPTIVE RADIATION

*no new phyla have evolved since this time*

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Basic definition: adaptive radiation

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accumulation of diversity in bursts

time vs morphology on tree-graph (goes against Darwin/mod synth bc they said all change is gradual)

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GOULD!

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wondered about biological explanation (lineage splitting?) *punctuated equilibrium*

form vs function --> function is limited by structure

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Basic definition: punctuated equilibrium

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morphological change occurs very rapidly (speciation) then stasis

vs. Modern synthesis that states it was a rapid change in the ENVIRONMENT & evol. change happened in small isolated populations

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FORM vs FUNCTION

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Gould.

adaptation can only do so much, the FUNCTION is limited by the STRUCTURE

Darwin brought these together...structure adapts by natural selection

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FIVE MASS EXTINCTIONS

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-end-Cretaceous (dinos)

-end-Triassic

-end-Permian (impact hypothesis/Deccan volcanism)

-end-Famennian

-end-Ordovician

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impact hypothesis

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iridium anomaly - large meteorite

...mass extinction due to global environmental changes from meteorite impact

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3 methods of PHYLOGENETIC RECONSTRUCTION

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phenetics (neighbor joining//clusters)--distance matrix: Jukes-Cantor and Kimura 2 Parameter

cladistics (maximum parsimony)

max. likelihood (combo of the two)

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PHENETICS (multiple hits)

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p=# obs. diff. per site

K=# evolutionary changes per site*

clusters taxa based on genetic distance

get PHENOGRAM based on OVERALL SIMILARITY

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Jukes-Cantor model

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each base substitution probability is the same

(K= -0.75ln(1-4p/3)

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Kimura 2-parameter model

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TRANSITIONS (P) VS TRANSVERSIONS (Q)

(A/G or C/T transition more likely)

a=1/(1-2p-q) b=1/(1-2q)

K=0.5lna + 0.25lnb

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CLADISTICS (maximum parsimony)

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use cladogram to then CLASSIFY organisms

synapomorphy=shared, derived character

autapomorphy=unique, derived character

homoplasy=analogy

draw all poss. trees, then most parsimonious is accepted

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equally parsimonious trees

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find a consensus hypothesis; "unresolved nodes"

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MAXIMUM LIKELIHOOD

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character state data to reconstruct (cladistics) then statistics to include probability (Kimura 2 parameter) to get calculated LIKELIHOOD

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CHARACTER MAPPING...

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..to infer traits homologous or analogous

...to infer ORDER of evolution of diff traits

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*Molecular evolution* (basics)

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nothing can change without variation: evolution cannot occur w/o >= 2 alleles in population

Allele freq, genotype freq, etc.

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discrete generation model

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all indiv. in a generation are same age and grow/reproduce together

gametes --> GENE POOL

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Hardy Weinberg as NULL HYPOTHESIS (4 things)

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1. no mutation/migration (no new alleles)

2. no selection (all same chance)

3. no "random" events

4. random mating

*all are true, allele freq/population strxr WILL NOT CHANGE*

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3 MECHANISMS THRU WHICH POPULATIONS EVOLVE

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-genetic drift

-natural selection

-mutation

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MUTATION as mechanism of evolution

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-doesn't contribute to allele freq between generations, just INTRODUCES NEW ALLELES FOR NATURAL SELECTION TO ACT ON

(mainly transitions and transversions)

*recombination introduces new combos of alleles*

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SELECTION

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adaptive evolution - diff in fitness--DIFFERENTIAL SURVIVAL=subset of indiv. involved in reprod.

INTERAXN BTWN GENOTYPE AND ENVIRONMENT

~Darwinian fitness~

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Basic definition: Darwinian fitness

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avg genetic contribution of indiv. with specified geno/phenotype to the next generation

*depends on ENVIRONMENT

*absolute or relative

*not actual contrib, but propensity

--FITNESS VALUES=# reprod/total #

dP=change in allele freq as result of selection

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GENERAL MODEL OF SELECTION

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H/W genotype frequencies mult. by fitness values, divide by total to get PROPORTION

p2(w11)+2pq(w12)+q2(w22) each over the whole thing for proportion...

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SELECTION COEFFICIENT (S)

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normalize fitness values: divide each by largest value so that smallest becomes 1-s

-OR-

by smallest value so that smallest is 1, others s+1

assoc. w specific allele, homozyg. for that allele is 1+s

S<0=neg. selection; S>0=pos. selection

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NEW ALLELE IN POPULATION. FREQUENCY?

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1/2Ne

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directional viability selection

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increased frequency of favored allele until it becomes FIXED

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OVERDOMINANCE (heterozygote has highest fitness value)

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*NOT* directional selection

1+s and 1+t for homozygotes (1 hetero)

when dP=0, equilibrium freq is:

p=t/(s+t) because ps=qt

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GENETIC DRIFT

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random flux in allele freq between generations due to SAMPLING ERROR (sample size inc, error dec.)

reduces genetic variation

probability allele is fixed = allele freq

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EFFECTIVE POPULATION SIZE (Ne)

(formulae)

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unequal M&F: Ne=4NmNf/Nm+Nf

fluctuating pop size: 1/Ne=(1/t)(1/N1+1/N2+...+1/Nt)

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drift will determine evol. fate of a population if...

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|s|< 1/2Ne