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Cell and Evolutionary Biology – Autumn Term
Life is Diverse, similar and adapted – Why? – caused early thinkers problems
Diversity – many different organisms
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Adapted –
organisms fit into their ecology (e
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carnivore’s carnaceal teeth, fish fins, birds wings)
Great Chain of Being – Plato, tried to order life importance – low – not alive – air  middle – living –
Lowest –slug, Highest – Man Highest – supernatural – gods
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Diversity – many different kinds of organisms on earth – massively different – e
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3 nocturnal
mammals – cats (sense eyes, interacts front paws), Bat (sense eyes, interacts – mouth), owl (sense
eyes, interacts feet)
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Similarity – even massively different organisms similar – e
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lions, cheetah, horse (breast feed),
snake, lizard (scales), heron, owl (feathers and flight)
Similarity means organisms can be organised by hierarchy
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E
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Homo sapiens – human (both plural + singul)
Adaptation primates – live in trees – grasping hands and feet to hold on, forward facing eyes to see
where going
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g
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BUT need
mechanism for this change
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Ds grandpa) – could not
think of mechanism
Jean – Baptiste Lammarck – thought of mechanism – organisms aquire characteristics in life – passed
onto offspring – driven by environment BUT demonstratably incorrect – proved wrong
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Collected flora and fauna, spoke about species problem, studied barnacles – proved animals not
plants – wrote “species theory” but hid it because it was against the churches beliefs
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organisms vary (some big,
small, tailed, no tail, even vary within species – Variation
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organisms look like parents – Heredity
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Organisms produce more offspring than can
survive (Malthus) pop outgrows resources, resources linear, pop exponential
MUST BE A STRUGGLE FOR EXISTANCE – competition, organisms that survive better – reproduce
more – make more copies, more organisms produced with beneficial variations
Differential Reproduction – best adapted organisms more offspring due to surviving longer
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g
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(used descent with
modification, not evolution
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CD thought finches were diff birds – realised NS caused finches to change over time to fill all niches
in Galapagos
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Diff between living and fossil – organisms became extinct, all living look diff to fossil
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Darwin didn’t know - where variation came from – if everyone same no NS, variation must occur for
NS to occur
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Must be particulate
inheritance
Mendel – monk pea plants – discovered how characteristics are passed down through generations –
traits disappear and re-emerge – NOT blending Yell + Green  Yell (Blending would = intermediate)
green reappears in later generations
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Genes cause characteristics! Genes cause NS!
Implications of Evolution - species naturally change over time, not fixed
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Similar organisms – species share common ancestors, inherit characteristics from ancestor
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NS predicts transitional fossils should occur – have characteristics of before and after
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Back limbspaddle like handsnostrils move backankles like artiodactyls haveliving cetacean
Evidence for recent/occurring change- peppered moth, Warfarin resistant rats, heavy metal resistant
plants, Galapagos finches, HIV, guppies
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E
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Comparitive Biochemistry – compare proteins - the products of genes
See how similar proteins used to be/are to each other
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DNA - compare DNA bases of living organisms – all have same DNA type, all from 1 origin of life,
genetics confirm relationships inferred from morphology
Point of evolution – copying – as soon as copying possible, it continued
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NS acts on genes, genes copy themselves
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Organisms are the tools/ways genes can copy themselves
Eat  Energy  movement  copying
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2nd Mechanism for change – sexual selection – dependant on mate
choice, males signal – females choose, females must be choosy
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Sexes may be separate (verts/insects)
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Female – Large, not motile, few made, Parsemonious (egg)
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Females invest more – reproduction, incubation so must be choosy
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Primary sexual characteristic – internal + external anatomy, organs for facilitating mating (claspers),
organs for young nourishment
2nday sexual characteristic – nothing directly to do with eggs+sperm/nourishment of young
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Males heavier – Northern elephant seal M3x larger, claim best territory if bigger, females map onto
resources
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Ornamentation – birds of paradise – male brightly coloured plumage female drab
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Dimorphic Behaviour – courtship rituals – dance e
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peacocks, sing
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Weapons – best wep, fight off other M get access to F, F want best territory – kudu horns, stagbettle
mandible
Mechanisms for sexual selection – Inter-sexual – selection produced by 1 sex preffering some
characteristics of other sex
Inter-sexual competition – more important for the sex which is reproductively limited by access to
other
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If M provides parental care, F may need access to other (seahorse)
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Both
provide care – usually monogamous species (bald eagle)
Choosing a Mate – low young investment – less choosy (usually M)
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Mate lots  more
copies  change in pop over time
High variance in pop  high competition to be a successful mate
Low variance in pop  low competition, reduces selection pressure
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Polygamy – Some individuals mate with several others – Polygyny – 1M SevF, Polyandry 1F, SevM
Polyandry very rare – occurs in strange circumstances due to limiting factors
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Mate competition – Monogamous – nearly all mate unless sex ratio skewed, this is corrected in next
generation
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M + F care for young (Albatross, Owl Monkey)
Polygynous species – some males breed a lot, some breed little or none – high comp between M,
high dimorphism – M larger/ornamated, F care for young
Polyandrous species - leads to high intrasexual competition between F for M, low dimorphism but F
may be bigger/ornamated if completion high, M or F+M care for young
Sexual selection = behaviour – requires that choosiness is always present, behaviour must evolve,
evolved behaviour = instinct
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Instinct – CD recognised behaviour evolved as instincts, looked for links between humans and other
animals in behaviour, emotions in particular emotions are evolved instincts
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Result of external predator pressure – follow rulessurviveemergent property
Fight or Flight – unconscious threat response – every organism has increased pulse + breath
– more O to muslces, dilated pupils – see more, fat into blood – energy
Good Fight/Flight = more copies
Altruism – problem – behaviour is to help another at cost to yourself
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Does help closely related organisms – help copies of your genes
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Biological Species Concept – an interbreeding pop whos members can produce fertile offspring but
cannot interbreed with other pops, Reproductively isolated
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E
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coelacanth – all same size unchanged for years
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Species changes over time e
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peppered moths,
resistance to pesticides – can lead to speciation
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How do new species arise – microevolution (evo at small level) small changes add upchange so
great new species identified
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Series of changes when lineage does no
split – no splitting event
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Exist
together, caused by splitting events, splitting events – cladogeneic event – causes splitting in lineage
If only anagenesis only occurred, there would only be one species alive now
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Variation in environment – some individuals prefer to live in slightly diff part of habitat, 2 diff areas
 2 diff pops – change over time
Variation in behaviour – want to mate at different times
Emigration, (founder effect) – individuals move, cannot get back, cannot mate reproductivley
isolated  2 species (grand canyon squirrels, split by canyon formation  2 daughter species)
2 directions of change – Divergent evo – similar animals – different adaptation – chimps + us
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53M not 314M)
Cladogenic Speciation – splitting events, allopatric or sympatric
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Sympatric – same place speciation – still diverge – behaviour/niche change
Isolating Mechanisms – offspring – reduced fitness/infertility,
Mating does not produce offspring – gametes do not fertilise each other, resulting offspring does not
develop properlydeath
Mating cannot occur – isolation (geographically/habitat), behaviour (different –mating times/dance)
mechanism (bits don’t fit)
How do new species arise – reproductive isolation – no/reduced gene flow, diff selection pressure
and drift lead to divergence over time – breeding cannot occur
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Microevolution/Macroevolution – same thing
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But what constitutes a new adaptive zone? – SUBJECTIVE!
Cladistics – branching diagrams of evolutionary relationships – clade = branch, based on branching
diagrams
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Fundamental tennets – things that need to be applied, classification should reflect phylogeny,
phylogeny should be determined by derived traits - synapomorphies(e
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shared derived shape,
changes that have occurred in evolutions course, share novelties – group together e
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birds
feathers, mammals mammary glands),
Arrangement of taxa within most synapomorphies is most likely
Common ancestor and descendants grouped accordingly to shared characteristics
Cladogram used – no time or higher/lower, taxa at same level – shows how closely related
organisms are – same level because everything has been evolving for the same amount of time
Organisms – cannot be primitive or derived, only characteristics can be primitive or derived, every
organism alive has a mix of primitive or derived characteristics e
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1 finger, more derived than 5
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Closest relatives are included, they are each others closest relatives, share characteristics, no
exclusions so no info lost
Paraphyletic – ancestor + some descendants – bad grouping – does not make a clade
Polyphyletic - some groups, no ancestor, ancestor missed out – groups are not each others closest
relatives
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THIS caused cladistics to be ignored till 1970’s – then show cladistics produces replicable + scientific
trees – 40% of characteristics evolved convergently – life finds answers multiple times – homoplasy –
converged traits
Genetic info can now be used to prove that in most circumstances morphology was right – genetics
incorporated with cladistics to get best arrangements
Darwin didn’t know where variation came from – how inheritance worked
No new variation – nothing to select – no natural selection
No inheritance – no passing on of traits to offspring – NS breaks down
Variation - new variation needed for NS to select, breeders report sports, organisms showing
variation – mutated, variation is mutation
Mutation - macro – wingless fly, micro – sickle cell anemia (small change – 1 base big effect Death
– no copies left)
Gregor Mendel - austrian monk – gardener + maths – investigated pea plant crosses
Chopped off stamens of pea plant (no self feritilisation) covered plant (cannot be pollinated by air)
Mendel then chose when to pollinate – knew genotype of peas this way as original plants
Homozygous for colour – produced 1 allele of each colour per egg/sperm
Purple + white  first gen purple – purple dominant – shows particulate inheritance (not mixing)
2 First gen purple  75% purple + 25% white! – all 1st gen carried recessive white allele
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Punnet/Mendelian Squares – DOMINANT and recessive, show genotype and phenotype of offspring
Law of Segregation – true breeding parents have identical alleles, gametes produced by 1 parent –
same allele – offspring has 1 allele from each parent
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Test cross – find genotype of a purple plant – mate with white plant - if all purple PP parent, if ½
white Pp parent
Linked/Separate characteristics – test for linking – 2 alleles per gene system – 4 alleles in each seed
Do test cross with true breeding plants – mate f1 gen – know genotype DrDr (phenotype dominant)
If linked – F2 generation 3:1 ratio of offspring, if not linked – 4 possible combinations of alleles
Mendel – did 100s of test crosses, to obtain ratios – found colour + texture are independently sorted
– genes are on diff chromosomes
Blending Inheritance – visible in carnations – Red + White  Pink!, looks like blending, due to
partial/incomplete dominance/codominance - neither allele completely dominant – intermediate
occurs – phenotype always = genotype
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Polygenic inheritance – several genes responsible for a characteristic, e
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height – 6 genes7
genotypes, looks as if continuous distribution – looks non particulate – actually individual particulate
polygenic inheritance
Mendels work ignored, CD work ignored – didn’t know how inheritance worked
Thomas Hunt Morgan – mutationist – though CD ideas interesting but not testable, sceptic of CD due
to inheritance knowledge, didn’t think inheritance explainable, worked with Drosophila
Melanogaster (fruit fly) – 2 gen in 1 week – quick, not much food/space needed – only have 4 large
chromosomes – visible under microscope
Repeated Mendels work – rediscovered mendels rules, tried to publish, mendels work found
Morgan documented mutation  variation of generatins of fruit flys – believed mutation needed
only, thought NS a weak force and not needed
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Morgan – showed genes carried on chromosomes – discovered sex cells + body cells
different (haploid ½ + diploid 2 ½ 1 from M, 1 from F)
Sex linked inheritance – 1 pair of chromosomes determine M (XY) or F (XX) – some characteristics
only found on sex chromosomes
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Used to map mutations without knowing which chromosome mutated, used to discover info stored
on chromosome
X/Y system not only – social insects have Hap/Dip
Transmission of sex linked recessive genes – recessive gene hidden in 1 sexes chromosome (usually
female) – produce pattern – some individuals carry  unaffected phenotype
Because on sex chromosome – 1 sex never shows, 1 sex shows sometimes if allele combination right
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Organisms – vary due to mutation, reproduce exponentially, pass on traits via heredity
Sexual selection – occurs as well as NS – intra – between same sex for mate, inter – one sex picks
other
Genes – inherited in particulate manner, located on chromosomes in nucleus, find approx position
on chromosome from crossing over maps
DNA – codes for AAsproteins create phenotypic traits
Alleles in pop – allele frequency - frequency allele shows in pop, x% of individuals that posses that
allele, changes over time
Hardy – Weinberg Theorm – null model for no change, if conditions met allele frequencies will stay
the same in subsequent pops – no change – no evolution, pop in equilibria in terms of alleles
Conditons needed – 1 – infinite population size – non infinite pop causes genetic drift – not everyone
repdroduces due to chance NS occurs, bottleneck effect – very few individuals reproduce – rare
alleles rarely used, surviving pop have different allele frequency
Occurs close to extinction – cheetah – kill parents for cub, pop plummets, remaining pop reproduce,
pop now very closely related, increased genetic disease  offspring deaths
2 – no immi (in) or emigration (out) – gene flow – if organisms come in/leave – gene flow, new genes
brought in/some lost as leave
3 – no mutation – introduces new genetic material – changes allele frequency over time e
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macro –
4 legged duck – micro – plumage colour change
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BUT proximity issues – cant reach all, even in sessile
organisms sperm and egg must meet – more likely if nearby
5 – no selection – no organisms better/worse at what they do than others – BUT struggle for life so
organisms are better/worse off
Hardy Weinburg theorm hardly ever occurs change occursevolution occurs continuously + at all
times everywhere
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If alleles recessive – only
cause death with homozygous recessive e
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sickle cell anemia – recessive + lethal, rods made not
spheres – don’t carry O2  death, should be low allele frequency, present in high frequency in
malaria zones
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Sickle cell hetero + malaria  
Sickle cell homo death, Sickle cell not present + malaria  death

No malaria – decrease in sickle cell frequency
Natural selection – cannot look forward/back/other places – explains adaptation
Lineages – split = clado, no split – ana
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Individuals selected for/against
Allele frequencies/pops change over time



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