UF BSC2010 Exam 3

Unifying principles of biology

evolutionary theory according to Theodosius Dobzhansky

Evolution

a change in genetic composition of biological populations over time

Scientist are able to demonstrate and observe evolution by?

fossil records

laboratory experiments

natural populations

Evolutionary theory

includes the entire set of ideas about HOW evolution takes place

Why should we care about evolution and evolutionary theory?

diseases

agriculture and industry

conservation

small populations evolve more rapidly

Characteristics of a scientific theory

well-supported

parsimonious

simplest explanation

falsifiable

leads to predictions that can be tested

Predictions of Evolutionary Theory

1. Spatial and temporal patterns in fossil records

2. Genetic Variation in most traits

3. A hierarchy of relatedness

4. Demonstrate evolutionary processes

Early Theories of Evolution

Eramus Darwin

Agreed that the population and species

change overtime- he had no evidence

Jean-Baptist Lamark

Looked at fossil evidence and noted that

organisms do change overtime. He concluded that offsprings inherit traits that the parents acquired which allowed them to become better adapted. (wrong) First to propose a mechanism of evolution.

Darwin was influenced by two academic works which where....

Charles Lyell's, Principles of Geology (1830)

Geologic uniformitarianism- natural process have been at work for years and explain geography changes.

Thomas Malthus, An Essay on the Principle of Population 1789

Populations may grow quickly at first but their growth will eventually decrease due to limited resources

Evolution through natural selection

Species change overtime and are different from common ancestors because of ns. Individuals with desirable traits are more reproductively fit and thus pass their genes on to the future generations. Less favorable traits are less like to reproduce...

Three key concepts of natural selection

- population must exhibit some variation in traits

aka genetic mutation

- the trait that exhibits variation must be heritable

- trait must impact an individual's reproductive success

Evolution is CHANGE IN POPULATIONS not individuals.

Natural selections is ONE MECHANISM by which evolution occurs.

Alred Wallace and Charles Darwin

Charles was developing his idea from 1830s but would publish it until he gathered enough information. Alred Wallace, independently, created a similar theory of evolution.

They both co-published the theory in 1858. But, the break though came from Darwin's published book- On the Origin of Species.

Charles Darwin discovered natural selection by observing artificial selection

What is the basis of theory of evolution by natural selection?

He noted that more individuals are born that can survive to reproduce and that individuals tend to resemble parents. So, individual differences can help increase or decrease the chance... Therefore, beneficial traits will increase in frequency in future generations

Gene pool

sum of all the alleles for a particular locus found in the population

Adaptions

favored by natural selection; process by which the trait emerges in the population

The populations must exhibit some variation in a trait

genetic mutation; change in nucleotide sequence- bad, neutral and good mutations

natural selection can only act on existing variation

The trait that exhibits variation must be heritable

phenotypic variation sources are genetic variation and environmental variation

Vp= Vg + Ve

H^2= Vg/Vp

It is the fraction of VARIABILITY that is genetic and not a fraction of the trait that id determined.

IF ALL HAVE THE SAME GENOTYPE= then Vg is 0 and heritability is 0

IF ALL HAVE THE SAME ENVIRONMENT= the Vg would equal Vp --> heritability would be 1

Parent offspring regression line

which relates the values for the traits of an offspring with the values for the traits of its biological parent

Natural selection has the greatest potential to shape traits in a population when traits have ____

high heritability

Breeder's equation

response to natural selection in terms of heritability of the trait and selection differential

R= H^2 x S

S= measure of intensity

Allows people to predict the strength of the response towards artificial selection.

Three Modes of Selection

Directional

Stabilizing

Disruptive

Directional Selection

When extreme phenotype is the fittest and that trait moves in the direction of phenotype. There is an evolutionary trend for entire frequency distribution to shift toward extreme direction.

Positive: favors trait on the high end of phenotypic spectrum (right)

Negative: low end (left)

The means changes, but variance (spread) doesn't.

Stabilizing Selection

When genetic variation decreases as the population stabilizes on an intermediate trait.

Frequency of each phenotypes changes and fitness varies... variance distribution becomes slimmer.

mean stays the same

EXAMPLE: human birth is stabilizing around 7-8

Disruptive Selection

When an intermediate trait is selected against and that traits tend toward both low and high extremes in phenotypes.

Emergence of two sep. species....

looks like "m"

Population genetics

study of how evolutionary forces cause allele frequencies to change over time

How to calculate Genotype frequency

# of individuals with the genotype of interest / # of individuals in the population

(or) fAA= NAA/N

FREQUENCY is between 0 to 1

SUM is equal to 1

How to calculate Allele Frequency

# of copies of a particular allele in pop./ # of copies of all alleles in pop.

(or) f(A)= 2NAA +1NAa / 2N

Genetic structure

describes the frequency of different alleles and genotypes in that population

p=1 or q=1 then its is a fixed allele- monomorphic

p<1 or q<1 then they have more than one allele on a locus- polymorphic

Basics of Hardy-Weinberg equation

p^2 + 2pq + p^2 = 1

states that allele frequencies should stay the same between one generation to anotherr... if it isn't then evolution is occuring

Assumptions of Hardy-Weinberg equillibrium

- no mutations

- no selection

- random mating

- population is infinitely large

- no gene migration between populations

if one isn't followed --> evolution

Genetic drift

unpredictable, random fluctuations in allele frequencies from one generation to the next because of a population's small size

random and unpredictable

larger impact when population size is smaller

( part of genetic drift) Fixation

occurs when one allele is lost and the other becomes the only one present in the population

basically gone forever

speed depends on side

The bottleneck effect

reduction of a population, usually natural disaster, such that the surviving population is no longer genetically representative of the original population

loss of genetic variation/diversity

example: cheetahs and elephant

The founder effect

when a few individuals become isolated from a larger population, with the result that the new population's gene pool is not reflect of original population

incorporates gene flow**

examples: lady bugs and tristan da cunha

Gene flow (migration)

genetic ADDITIONS or SUBTRACTIONS from a population, resulting from the MOVEMENT of fertile individuals or gametes

exchange of genetic information by migration

usually leads to reduction of differences by introduction of new alleles ( increases diversity )

Two factors:

- number of migrants

- size of the population

Comparing Gene flow to Genetic drift

Gene flow= can increase genetic diversity

migration and reproduction

exchange of information

Genetic drift= tends to decrease genetic diversity

random events leading to small size

Selection

acts on heritable variation- introduced by gene flow or mutation- favors the trait that lead to reproductive fitness and promotes adaptive evolution

higher fitness if it passes more alleles

Processes that create/maintain variation

Mutation- "creator"

Migration ( gene flow )- introduce

Disruptive selection- maintains multiple phenotypes

Neutral Evolution

Two kinds of mutations

- synonymous substitutions

- nonnsynonymous substitutions

Synonymous substitutions

nucleotide substitution has NO AFFECT on amino acid and phenotypes

silent mutations

more than one codon can code for the same amino acid UUA/UUG

Nonsynonymous substitutions

substitutions DOES change amino acid and affects phenotype

inserting different codes... missense

can be under selection

Nonsynonymous substitutions TYPES

Frameshift: adding or subtracting nucleotides

Nonsense: premature stop

In general

rates of syn. are higher than nonsyn.

( rates of silent mutation are greater than alterations in amino acid sequence )

substitutions in PSEUDOGENES are higher- no longer functional (syn. are more likely...)

Neutral Evolution

most molecular variation in most populations are selectively NEUTRL, meaning they don't convey a selective adv. or dis.

so genetic drift explains accumulation (not selection)

***Rate of fixation equation

2Nu x 1/2N = u

***Molecular clock

approach to calculating the amount of time since two species diverged

How to determine whether a particular portion of the genome is under....

- positive

- neutral selection

- purifying

Positive selection

more nonsyn. than syn.

directional selection!!

Neutral selection

nonsyn. and syn. are equal

genetic drift changes don't provide adv. or dis.

Purifying selection

nonsyn. is less than syn.

more resistant to change (silent) allowing stabilization

Genome Size, Organismal Complexity and population size

there is a strong correlation between organismal complexity and the size of the coding portion of an organism's genome

noncoding proteins STILL maintain chromosome structure etc... some have parasitic transposable elements

population size influences have effective selection is at weeding out

Genome evolution includes

- sexual recombination

- lateral gene transfer

- gene duplication

Sexual recombination

during meiosis-> genetic variability- selection can act

Asexual vs. Sexual

sexual evolved from asexual...

Sexual disadvantages;:

- reduces rate of reproduction

- reduces rate of gene transfer from mother (50%)

Sexual advantages:

- can separate malicious gene combinations

- homologous chromosomes can be used to repair DNA

- increase genetic variation ("shuffling") ( new combinations for selection to act on )

Asexual:

- no way to eliminate mutations

- every offspring is similar

Lateral Gene transfer

process by which genes, organelles or fragments of entire genomes move from one lineage to another

aka horizontal gene transfer

transfer genes from other species like viruses and bacteria

Gene duplication

when an entirely new copy of a gene appears in a genome over evolutionary time

- increase in production of protein

- genes can be expressed at different times

- one original, other accumulates deleterious (pseudogenes)

- one original, accumulates advantages (new function)

What is more likely to occur with gene duplication...?

- directional selection; because the original gene is free to serve it original function

- when an entire genome is copied then opportunities for evolution of a new function may occur

Gene family

a group of homologous genes that have related functions- from gene duplications and subsequent evolution

Evolutionary developmental biology

field of biology that compares developmental process of different organisms in an attempts to determining the ancestral relationships between them and how the developmental process evolved

Fibroblast growth factor (Fgf8)

outgrowth of the limb- expressed along the outside of the growing limb bud (apical ectodermal ridge)

Sonic hedgehog (Shh)

determining which digit is which- poster side of growing limb (zone of polarizing activity)

Animals inherit a basic genetic framework for embryonic development from a common ancestor....

snakes, mice and chickens alike

Speciation

The process in which biological lineages diverge due to reproductive isolation, resulting in new species

Three species concepts

- Morphological

- Biological

- Lineage

Morphological species concepts

based on OBSERVABLE morphological characteristics- body shape, size, color, structure, etc.

**easy to apply

Morphological species definition was by

Carlos Linnaeus - binomial nomenclature

birdwatchers

Problems of morphological species concept

1. Members of the same species may not look alike

(caterpillars look nothing like butterflies)

2. Members of different species may look similiar

CRYPTIC species look alike but cant interbreed

( male and female ducks have diff. features and age appearance )

( frogs look alike but can't breed- tetra. & diploid )

Biological species concept

by....

Ernest Mayr

"groups of actually or potentially interbreeding natural populations that are reproductively isolated from other such groups"

importance: isolation

horse and donkey can mate but aren't fertile.... (ex)

Problems of biological species concept

1. Doesn't apply to asexual organisms

( prok. wouldn't be a species then...)

2. Definition can't be applied to extinct animals

( fossils can't tell us about isolation- we make inferences )

3. It isn't clear what "potentially interbreed" really means

( ... could in the future- organisms can mate, but can be infertile )

** Ring Species

4. Definition is impractical

( we can't cross each organism to determine if they can interbreed )

5. Infertility is an ancestral characteristics

( when two species arise from one, they often remain infertile for a period of time before they are reproductively isolated )

Lineage species concept

by

GG Simpson

two groups that share a branch on the tree of life

relies on molecular similarity and phylogeny

( Cali. ravens and Canada ravens would be diff. species )

Morphological= reproductive isolated species undergo physical changes

Biological= reproductive isolation results in evolution of distinct lineages over time

Role of reproductive isolation

most important factor in speciation

speciation REQUIRES an interruption in gene flow between two groups... to evolve

How can gene flow be disrupted??

- habitat selection

- assortative mating

- geographical barriers

Dobzhansky-Muller model

explains how a single lineage can split into 2 reproductively isolated species

subdividing a population...

alleles will not be unable to mix-> different species

How isolation of gene flow occurs?

- allopatric speciation

- sympatric specitation

Allopatric speciation

population is divided by a physical or geographic barrier, forming two isolated populations that evolve independently

other homeland

Via dispesal or vicariance

Dispersal Allopatric Speciation

moving to a new area that is separated from the rest of the population and colonize- this is called FOUNDER EFFECT

Galapagos Finches-> migrated and developed different characteristics

Hawaiian honeycreepers

Vicariance allopatric speciation

climate change, glacial advance and retreat, etc.

Freshwater steam fishes-glacial advance divided them

Panama- land arose and separated Caribbean and Pacific populations

Sympatric speciation

species arise from a population that remains connected

Hint-- SS, same

Two types of sympatric speciation

- disruptive speciation

- polyploidy

Disruptive sympatric speciation

favors two extremes in same population from behavioral difference

palm trees that prefer different soil

Polyploidy sympatric speciation

mistake during cell division results in an individual with cells that have more than one copy of the genome

generally viable but genetically isolated, can't reproduce normally with others

Two kinds of polyploidy sympatric speciation

- autopolyploidy

- allopolyploidy

Autopolyploidy sympatric speciation

duplication of a set of chromosomes WITHIN a single species

Allopolyploidy sympatric speciation

when the chromosomes of two DIFFERENT species are combined

combine chromosomes by interbreeding- forming a hybrid with abnormal chromosomal number

Incipient species

species that are in the process of diverging into separate species but they can currently interbreed

Two possibilities of incipient species...

1. reinforcement

hybrids might be less reproductive- NS will favor parents who mate with their own kinds that parents who hybridize

2. merger

hybrids are as fit as non-hybridizing

can become a single species again

Prezygotic isolation mechanisms

mechanisms

temporal

behavioral

habitat

gametic

Mechanism Isolation

anatomical differences

the right "fit"

"match" between a plant and pollinator

Temporal Isolation

isolated that they never have the opportunity to reproduce

breeding time

Behavioral Isolation

animals have mating rituals that must occur

acceptance

Habitat Isolation

animals are isolated by space and never have the opportunity to come into contact with one another

relates to pre.