Evolution

Soft inheritance

environmental forces can cause organisms to develop traits within their lifetime that are passed to offspring (not very true)

Charles Darwin (Origin of Species) 5

1.populations have tremendous growth potential (still remain stable)

2.natural populations must be limited (struggle to exist)

3.individuals are variable (not all the same)
4.offspring resemble parents (variation is heritable)

5.individuals best suited to enviornment survive and reproduce

evolution

change in genetic compositionof a population over time

Natural selection

evolutionary process by which individuals best adapted to their envirornment survive and reproduce

Evidence of evolution

-artificial selection

-homology

-vestigal structures

-fossils

-molecular biology

-direct observations and experimental evidence

Artifical selection

selective breeding of organisms by humans

Homology

similar features from shared ancestry

Vestigal structures

structures that have lost original functions

fitness

relative survival and reproductions sucess of an individual compared to other in population

Favored phenotypes become…

more common in future generations

adaptation

hertiable trait that evolved in a population through natural selection

Evolutionary processes

mutation

gene flow

genetic drift

non-random mating

more about mutations

-mutations arise randomly, low, constant

-10-9 changes

-large populations contain huge numbers of mutations

-mutation generate genetic variation—> material for evolution by natural selection

Gene flow

-transfer of alleles between populations

-through migration of individuals or movements of gametes

-changes allele frequency in a populationn

(birds crossing over mountain into other population)

Genetic drift

random change in allele frequency over time

bugs with specfic allele die randomly

-larger effect on small populations

-population bottleneck +founder effect

GD-Bottleneck effect

large decrease in population size where only a few individuals survive will result in randsom loss of genetic diversity

-little left and reproduce and lower diversity

GD-founder effect

-small group of individuals establishes a new population resulting in a random sample of original population’s alleles

-group leaves big population and is a random sample of og

Non-random mating

-type of sexual selection
-occurs when individuals choose mates with particular phenotypes

-changes allele frequency

sexual selection

can occur when individuals of one sex mate preferringly w individuals of another sex NOT random

Allele frequency

p=number of copies of the allele in pop/ total number of copies of all alleles in the pop

hardy weinberg

-simple equation to show that allele frequencies in a pop do not change when no evolution occuring

H-w assumptions

-no mutations

-no selections

-no gene flow

-random mating

-population size is infinite

natural selection graphs

stabalizing, directional, disruptive,

Stabilizing

occurs when mean phenotype has higher fitness than the extreme (before and after selection)

Directional

occurs when extreme phenotype has higher fitness than the average phenotype

-mean value shifts

-traits disappear and gene variation can be reduced

Disruptive

both phentoypes have higher fitness than the mean\

-unchanged, but genetic variation increases

Maintaining genetic variation

-diploidy

-heterozygote advantage

-temporally varible selection

-spatially variable selection

Diploidy

hides recessive allele in heterozygotes, preserving genetic variation

C over c, hides c

Heterozygote advantagte

heterozygotes have higher fitness than homozygotes, maintainng multiple alleles in population for breeding

Temporally variable selection

changing enviornments favor different phenotypes at different times, no fixed alleles

-want small beak birds one time want big beak birds another

Spatially varible selection

occurs when different local enviornments favor different phenotypes (dark mouse in datk cave, light mouse in sand)

Evolution constrained by…

physics and chemistry

genetic variation (no genetic variation= no evolution)

history

trade offs

Evolutionary history

the origins of a trait can restrict it from evoling differently

-our eye used to need to protect the cones so we see less color and stuff—> this cant evolve

Trade offs

a trait that improves fitness in one area reduces fitness in another

-hip sizes

Chapter 20

Biological classification

-classification based on observable traits

-taxa-named group of an organisms

-taxonomy- describe, name and classify organisms into groups 1

Phylogeny

evolutionary history of a group of organismsph

phylogenetic tree

diagrammatic hypothesis about evolutionary relationships among species

Node

connection from common acestor and splits off (the split off)

Root

oldest common ancestor

horizontal branching order +length

over time

vertical branching order

nothing- can switch branches

sister taxa/clades

lineages that share most recent common ancestor

clade

group that includes an ancestor and ALL descendantsm

monophyletic

(a clade)- ancestor and ALL descendants

paraphyletic

contains common ancestor and some descendants (one branch not included)

polyphyletic

groups that does not include include common ancestorco

common traits used for phylogeny

morphological traits

molecular traitsm

morphological traits

-prescene, size, shape, other body parts

molecular traits

DNA and protein sequences

build a tree

compare traits among taxa, group taxa that share the mpst traits derived traits together, identify shared derived traits that indicate common ancestry

Plesiomorphy

ancestral trait for a particular clade

apomorphy

derived or changed trait for a particular clade

synamorphy

dervies trait that is shared by members of a clade (NEW)

-used to identify clades and reveal patterns of shared evolutionary history

Problems making a tree

-homoplasy

Homologous traits

have shared similar evolutionary origins

analogous traits

evolve independently for same function (convergent evolution)

evolutionary reversal

lineage reverts to an ancester trait

(whales return to aquatic animals even though a mammal)

parisomy principle

best phylogenetic tree requires the fewest evolutionary changes

trees can be used trace…

origins of behaviors such as mae preferences

molecular clock

methods that uses rates of genetic change to estimate evolutionary time

-study timing of historical and recent events

Chapter 21

more time since divergence…

more sequence differences

homologous sequences

sequence shared among species due to common ancestry (even if changed)

sequence alignment

allows us to compare homologous DNA positions across origanisms and identify evolutionary changes

number of changes among sequences are underestimated because of…

-multiple substitution

-coincident substitution

-parallel sub

-back sub (reversion)

multiple sub

multiple one nucleotide change over time

coincident substitution

mutation in same spot over time into 2 diff nucleotides

parallel substitution

mutation in same spot over time into same nucleotide

back substitution

revert back to ancestral sequence

synonymous sub

no phenotypic effect, no amnio acid change

neutral to natural selection so they accumlate over time

nonsynonymous

alter protein function

-Most delete

-some neutral

-some benefical

rates of nonsynonymous…

typically lower than rates of synonymous sub

-most sub happens in pseudogenes

rate of non syn to syn=

neutral, purifying selection, positive selection

<1

purifying/stabalizing selection

=1

neutral

1>

positive selection/directional selection

neutral

mutations spread or disappear by chance

positive selection

natural selection favors benefical mutation

purifying selection

natural selection removes harmful mutation

aligned sequences can be summarized using…

similarity matrix that counts similarity and differences between species

purifying selection in

most codons

pathogen binding sites experienece

positive selection

Genome evolution creates new traits

-genome size variation

-recombinant

-lateral gene transfer

-gene duplication

genome size varies, most variation is

noncoding DNA

recombinant

sexual recombination generates new genetic combinations

-avoids deleterious accumulation of mutations that can cause asexual repro (muller’s ratchet)

lateral gene transfer

moves genes across species boundaries, introducing novel functions that can rapidly alter evolutionary trajectories

duplcated genes can

retain same function (increase gene product)

diverge in expression (different tissues/times)

become pseudogenes (be eliminated, new function)

diversify functions

whole duplication of genome

-evole special functions in different tissues

Chapter 22

morphological species

group of organsims that are morphologically distinct from other groups

-different species look the same? members of same species look different

biological species

group of interbreeding populations that are reproductively isolated from other groups

repro iso

share a distinct gene pool

-needed for divergence and speciation

P: new allele that causes repro incompatibility cannot spread in population

problems w/biological species

-asexual species

-ring species that travel and isolate and reneter

-fossils cant breed

speciation

splitting one population into two that are reproductively isollated from one another

Dobzhansky-Muller

-explains evolution of reproductive isolation, harmless mutations can be harmful when combines across populations

1. physical boundary can caus ancestral population to become seperated (aa + bb)—> result in gene flow among populations

2. seperated populations evolve independently (Aa or Bb)

3. they become fixed in the divergent populations

4. reproductive isolation increases w degree of genetic divergence

5. hybrids have low fitness or dies or infertile

more genetic divergence…

more reproductive isolation

allopatric speciation

-occurs when populations becomes geographucally seperated or isolated by physical barriers OR

-most common mode of speciation

allopatric 2

individuals at the edge of a population become isolated by a barrier (peripheral isolaitonsy

sympatric speciation

occurs when repro isolation develops between segments of a population WITHOUT any ohysical barrier

-polyploidy

-disruptive selection