02. WHAT IS EVOLUTION? Flashcards
When does adaptation occur?
- environ change
- genetic variation advantages some indiv
- species survives long enough to reprod → pass on advantagous alleles
In what ways can a population vary?
- size
- distribution
- structure
⇒ det influ on evol processes
Define adaptation
- bio mechanism by which orgs adjust to environ changes.
- an inherited aspect of an indiv that enables it to outcompete others in specific environ. evolved thru NSe.g. Galapagos finches - diff beak sizes/shape dep on food source in environ
Define evolution
cumulative change in a pop/species over time
Define natural selection
- key agent of change that can cause evolution, whereby phenotypic variety w/in pop cause some indiv to survive + reprod + pass on advantageous alleles
- e.g. Galapagos turtles - long necked turtles
Define inheritance
when DNA/trait passed from parent → offspring during reprod
Key details about Galapagos islands
sml series of islands w range of ages → diverse ecosystems across islands → high biodiv → 5 types/13 species finches w/ variety beak shapes/sized = adapted to diff food sources
Define micro and macroevolution
- macroevolution: cumulative changes that occur in lg taxonomic grps over long time period - occur at or above species level e.g. emerence of new evol lineages/species
- microevolution: ‘agents of change’ that shape species’ genome
Define species
broadly defined as grps of similar orgs that a) share genetic info and b) interbreed to prod viable offspring
Outline the five ‘agents of change’
- natural selection: survival + reprod of the fittest
- mutation: primary source of genetic variety
- sexual reproduction: mating systems + recombo of genes
- genetic drift: random changes to allele freq based purely on chance
- gene flow: migration, movement, hybridisation
Defining features of populations
- grp of orgs that either interact + share genetic info OR are identical
- interaction = same place/time
- share genetic info = interbreed to prod viable offspring
- identical ⇒ reprod asexually - may also share genetic info
How does the gene pool of a population relate to evolution?
size of GP det evol impact
- sml GP = low genetic div = inc likelihood of allele fixation bc inc chance of GD
- lg GP = high genetic div = low chance of extinction (opp for selection) + inc chance mutation
How does population density relate to evolution?
- density of indiv from pop in specific area - LOCATION
- impact evol bc influ gene flow
How does population structure relate to evolution?
physical composition + social organisation of orgs det by mating systems (driver of evol bc sexual selection)
Steps in HWE analysis
Image 2
Conditions for HWE
- no mig
- no mutation
- equal fitness i.e. X selection
- infinite pop size
- random mating
Define polygenic
when specific phenotype is cumulative result of multi genes
What is the purpose of HWE?
provides allelic freq expected if X AoC acting on pop. we compare this info to observed allelic freq to deduce if pop = under influ of AoC-> predict evol
Under HWE, allele frequencies…
do not change over time
What is the d.o.f for allelic data?
1
What does it mean if a population’s allele Chi square is signficant?
Pop is out of HWE → likely under influ of AoC
- mig may be occuring
- mutation may have unexpected impact
- fitness costs + benefits may vary
- pop size may be sml
- mating may X be random
List the 3 ‘ingredients’ for NS to occur:
- variation - pop comprised of indiv w diff in appearance/behaviour/physiology e.g. fur colour, beak length, wing pattern etc.
- heredity - phenotypuc traits passed down from parents to offspring
- selection pressure - some phenotypes must offer better chance at survival long enough to reprod + pass down advantageous traits
Selection acts on _ alleles faster than _ alleles.
Dominant alleles are _ fixed but recession alleles…
- dom / rec
- never / can be fixed (never fade from pop)
Outline the different types of NS
- directional/positive - favours indiv on one end
- stabilising - favours indiv in middle
- disruptive - favours indiv on opp ends (often drives speciation) e.g. specialised feeding - sml fish eat algae + lg fish eat insects
- artifical - result of human activity - esp. common in crop selection e.g. corn, brassica
Balancing selection favours…
heterzygotes → maintain heterozygosity in pop e.g. sickle cell disease
How to calculate relative fitness
- Div O by E to find O:E ratio
- Div each O:E ratio by highest O:E ratio
- Div W of most fit (w=1.000) by w of next fittest to find selective adv
e.g. 1.000/0.894=0.118→ 11.8% more fit
What was the impact of NS on Galapagos finches?
variation in beak size
heredity of beak size alleles
selection pressure due to 1977 drought
→ pos selection for inc beak size
What was the impact of NS on rock pocket mice?
variation in coat colour
heredity of coat colour alleles
selection pressure from predators in pale sandstone & dark volcanic rock environs
→ impact coat colour of pop (black mice in dark volcanic rock area + white mice in pale sandstone area)
Why do mutations occur?
damage/misreading of DNA seq → change to DNA code
Why are mutations called the ‘source of variation’?
mutations → change DNA code → intro variation into pop
The impact of mutation depends on…
- size + location in genome
- regulatory region → impact gene EXPRESSION to varying deg
- coding region → impact gene FUNCTION to varying deg
Smaller vs larger types of mutation
- smaller changes
- substitution
- indel
- frameshift
- larger changes
- duplication/inversion
- aneuploidy
- entire genomes/chromosome duplicated
Outline the two broader types of mutation
- somatic - transmitted via asex reprod → affects all daughter cells of parent cell
- germline - transmitted via sex reprod → affects gametes (egg/sperm)
How do mutations impact evolutionary processes?
- mutations can impact gene pool of pop over time → minor changes to allele, under selection pressure, can sig impact phenotypic expression of pop over time
e.g. small change ⇒ sickle cell anaemia (point mutation) + teosinte to corn (point mutation) OR lg change ⇒ down syndrome (aneuploidy) + crop domestication (whole genome duplication event)
Compare sexual and asexual modes of genetic info transfer
- asex reprod
- fission, fragmentation, budding, vegetative reprod
- prod clones
- no change to allelic composition
- sex reprod
- recombo via meiosis
- sperm + egg
- prod novel offspring
- changes to allelic composition
- can occur thru union of 2 sep orgs (typically male + fem) OR same org (hermaphrodites)
Explain why sexual reproduction is evolutionarily advantageous
- combo beneficial alleles → generate novel genotypes → ‘faster’ evolution under selection → able to adapt to new/changing environ better i.e. genetic variation = beneficial for species survival
Explain why asexual reproduction is evolutionarily advantageous
- reprod faster
- lower E req bc X need to search for mate
- X risk STIs
What is random mating?
prob that two indiv in a pop mate is same for all poss pairs of indiv w/in that pop
Compare assortive and disassortive mating
- assortive (pos assortive) mating
- mate w indiv w same alleles = ‘like w like’
- X change to allele freq
- genotypic iso → phenotypic iso → w selection can cause speciation
- e.g. Olivella biplicata - lg animals live further up shoreline than smler animals → mate w similar size orgs
- e.g. primates
- disassortive (neg assortive) mating
- mate w indiv w diff alleles - opp attract
- outcome = novel genotypes → maintains genotypic variation w/in pop
- e.g. wolves
Describe mating behaviours in primates
- outcome: genotypic dilution
- promiscuity
- outcome: genotypic differentiation
- monogamy
- polyandry
- polygyny
Describe inbreeding/self-fertilisation
- outcome: inc homozygosity in all loci of genome → problematic bc delet recessive alleles may become more dom in pop
- problem for hermaphroditic plants
Define genetic drift
random + directionless changes in allele freq w/in pop
occurs due to ‘sampling errors’
How does population size relate to genetic drift and evolution?
sml pop size → inc prob of GD bc less alleles to choose from → sml events have proportionally greater impact on pop than in lg pops
Outline two types of events that reduce genetic diversity
- bottleneck event = drastic reduce pop size → dec genetic div → inc prob GD bc less alleles to choose from → inc chance allelic fixation/change to allele freq
- founder event = sml grp moves away → dec genetic div → inc prob GD bc less alleles to choose from → poss speciation over time if selection pressure bc iso from parent pop
What are the long-term impacts of a genetic bottleneck?
pop # may recover but genetic div may be lost forever
→ allele fixation
→ inc homozygozity
e.g. cheetah
Do populations need to be infinite in size for allelic frequencies to obey HWE?
no - they just need to be lg enough that random sampling errors X sig impact allelic freq
Provide two examples of how small mutations can have a significant impact
- sickle cell anaemia (point mutation)
- teosinte to corn (point mutation)
Provide two examples of how large mutations can have a significant impact
- down syndrome (aneuploidy)
- crop domestication (whole genome duplication event)
Define gene flow
transfer of genetic info from one pop to another
can intro new alleles
occurs via mig, mvmt or hybridisation
What is the difference between migration and movement?
mig = long dist bw distinct pops vs mvmt = intermingling of sub-pops
For gene flow to occur, individuals…
must be able to interbreed to prod viable offspring
t/f mating systems influ amt/pattern of GF
More porous geographic barriers correlate with…
higher connectivity
Connectivity…
- influences GF - geog barriers
- dynamic - season/weather dep e.g. river dries up
Define genetic hybridisation
interbreeding of indiv of diff spp to prod viable offspring
Equation for change in populational allelic composition due to migration
Δp=m(x-p)
m = mig rate
x = freq of allele in migrants
p = freq of allele in residents
Define speciation
evol process where new spp emerges due to reprod iso (LT inhibited GF)
one evol lineage split into 2+
Outline the three types of reproductive barriers that drive speciation
i.e. LT inhibited GF
- pre-mating iso
- geog iso
- behavioural iso e.g. mating calls
→ mutation, selection, GD
- pre-zygotic iso
- mating time diff e.g. coral spawn
- eco diffs e.g. diff plants attract diff pollinators
- post-zygotic iso
- fertilised egg/offspring = X viable/sterile e.g. leopard frog x wood frog
What type of reproductive barriers result in allopatric speciation?
pre-mating
What types of reproductive barriers result in sympatric speciation?
pre-zyg
post-zyg
What is special about elk and deer speciation?
allopatric distrib - elk in Nth Am + deer in Eur/Asia
GF ended 9000yrs ago but can interbreed to prod viable offspring - diff spp???
Species boundary can be semi-permeable because…
occasionally hybrid offspring ≠ infertile
Define adaptive introgression in the context of hybridisation
intro beneficial traits from one spp into another
e.g. Müllerian (??) mimicry in butterflies - all diff spp but same wing pattern to convince pred they are toxic
Define introgression
mvmt of alleles from one spp/pop to another
Modern humans’ DNA may contain Neanderthal DNA because…
hybrid + introgression
Molecular genetics involves…
sequencing + analysing specific genes → understand function
Molecular genomics involves…
sequencing and analysing entire genomes
→ ID regions under selection/resp for phenotypes
Genomic analysis involves…
- collecting samples/recording phenotypes
- creating libraries + sequencing
- investig gene loci/entire genome
- ID SNPs + other areas of genetic variation
Example of a phenotype with continuous distribution
height
also e.g. of human polymorphism
Genome sequencing enhances…
our understanding of micro and macroevol e.g.
What is a Genome Wide Association Study (GWAS)?
process of assoc genotypes w measurable phenotypes
Types of GWASs
- med research
- e.g. case vs control analysis
- evol bio
- understanding adaptations
- agri
- traits of econ value
- disaster resilience
What is a selective sweep?
strong pos directional selection in specific locus of genome
e.g. lactase persistence in Eur + Afr (Tischkoff et al, 2007)
→ removes pop variation i.e. dec genetic div
Lactase persistence in Europe and Africa is an example of…
convergent evol bc same gene selected on after 2 diff mutation events, resulting in same phenotype
How does a reduction in population size result in reduced genetic diversity?
dec pop size → dec # indiv reprod → dec gene pool → dec genetic div
Genetic bottlenecks impact allelic frequency…
randomly
Random mating means…
pop structure absent + mating occurs in prop w genotype freqs
Insignificant p-value when 1df
p>0.5
