Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

EVOLUTION
Key words:
Spontaneous generation: theory in which life develops from nonliving matter, e
...
, dust creates fleas
...

Microevolution: Changes in the frequency of a gene within a species, usually small changes over small time
periods and is observed during human time frames (life span)
...
g
...

Genotype: refers to the genetic makeup of an organism, complete set of genes
...

Macroevolution: change over time in the type and number of species over long periods of time between
species
...

Phylogeny: refers to the evolutionary history of species
...
E
...
calluses on fingers , larger muscle size , skills
like painting , singing , swimming , dancing
spatial diversification:

endemic: Unique to a certain place, not found anywhere else
descendent : someone that comes after
...

Gradualism: a theory that changes of organic life and of the Earth itself occur through gradual increments
Gap creationism= accepts the earth is old but accepts the bibles account of biodiversity
...
Accepts microevolution and parts of macroevolution
Theistic evolution = God invented the rules of genetics and mutation which resulted in natural selection and
evolution as part of a plan and let everything run
...

Autosomes :An autosome is any of the numbered chromosomes, as opposed to the sex chromosomes
...
Most importantly, they carry the same type of genetic information: that is, they have the same
genes in the same locations
...

Neutral mutation: Neutral mutations are changes in DNA sequence that are neither beneficial nor detrimental
to the ability of an organism to survive and reproduce
...
If they increase an organism's chances of surviving or reproducing, the mutations are likely
to become more common over time
...
For example, there is more than one possible trait in terms of a
jaguar's skin colouring; they can be light morph or dark morph
...
two groups of organisms are separated by a physical or geographic barrier
...

Cofactor: A cofactor is a non-protein chemical compound that is required for an enzyme's activity as a
catalyst
...
1 Greg Hurst)
➢
-

-

A change over time within a species (a change in their gene pool) a mutation arises which is
advantageous and spreads through the species over quite short time periods – microevolution in
observable time frames, normally within a species
...

Evolution theory is based on observation
...
g
...

Inference of macroevolution fossil records and ancient DNA provide evidence
...
Create phylogeny and infer how different species are
related and once shared a common ancestor
...


Why study Evolution? (1
...

Utilitarian = when we target things to kill like bacteria, they evolve to avoid it understanding of
evolution helps us with the management of drug/pesticide resistance
Evolution can be controversial as there are alternate views of biodiversity, may have problems with
the process of natural selection and our common origins as they may believe in creator theory

Pre-Darwinian ‘Organic Evolution’(1
...
Examples: calluses on fingers , larger muscle
size , skills like painting , singing , swimming , dancing

-

Charles Darwin and Alfred Russel Wallace(1
...
These advantageous phenotypes got inherited through generation
which led to a gradual change in traits within a population resulting in new species forming
Artificial selection can take a species to different phenotypes (breeds) if individuals with select traits
are chosen for breeding, if this were to happen naturally it would produce spatial diversification and
different species
3 conditions for natural selection = 1) individuals must vary in character 2) some of that variation
must be heritable and 3) mean numbers of variants differ in offspring produced
Darwin found that 50% of species on the Galapagos were endemic (unique to that places) and that
there was even variation between the islands

Darwin then proposed the idea of the One Tree of Life which suggested all species are interlinked and
share the same common ancestors
...
Processes like transcription and translation as
well as basic metabolism have been conserved
...
Its also important in a practical sense as
has allowed us to genetically modify organisms by extracting certain DNA sequences from one and
transferring them to another (e
...
creating insulin producing bacteria which aids treat type 1 diabetessame cell division processes and universality of DNA allow this to happen)
...
1 Greg Hurst) = Lamarck proposed that
individuals would form new habits in response to a change in their environment which would use them to use
a part of their body more or less to either strengthen or weaken it – change would happen during the course
of the individual’s lifetime and would be passed onto offspring as long as it mated with another who had also
gone through the same changes
...

These traits would be genetically passed on and become more and more widespread amongst the population
whilst the traits which didn’t aid survival slowly disappear
...


Lamarck did not believe species went extinct he only believed that they changed into other species on a
continuous journey to perfection- thought organism continuously evolved with increasing complexity and that
humans were the closest to reaching this said perfection
...


Similarities between Lamarck’s and Darwin’s theories(1
...
Both realised that species survived because
something in their makeup made them better able to get what they needed from their environment
...


Geological Evolution: (1
...
g
...
1 Greg Hurst)
-

YOUNG EARTH CREATIONISM views on diversity is a very literal Christian view in the sense that all
species were created separately in genesis designed by God 6000 years ago
...
Major cause of antipathy (dislike)
towards Darwin and his second book (the descent of man) which suggested we were the third

-

-

chimpanzee, our creation wasn’t special, but we were just another species as a result of biodiversity
...

OLD EARTH views accept that the earth is geologically ancient at 4500 million years old believe in
evolution and how biodiversity arose
...
Gap creationism=
accepts the earth is old but accepts the bibles account of biodiversity
...
Progressive creationism= accepts natural selection
and change occurring but has the belief that outside intervention is acquired
...
Theistic evolution = God invented the rules of genetics and mutation
which resulted in natural selection and evolution as part of a plan and let everything run
...

No necessity for conflict between faith and evolutionary biology
‘Through him all things were made; without him nothing was made that as been made (John 1:3) can
be taken literally (that god created all things individually) or metaphorically (theistic evolution- god
set life processes like evolution up in motion as part of a plan)
...
1 Greg Hurst)
-

If you believe in evolution and planetary processes that lead to biodiversity you lack faith in religion
which is the leading cause of the problems within society
...
There’s been attempts to
prohibit the teaching of evolution or try to force teach the religious philosophy on biodiversity
...
1 Greg Hurst)
-

Evolution is blind
External events produce new unpredicted trajectories
Evolution has no goal or orientation
Humans are not the pinnacle of evolution all species are on branches of the tree of life which link us
to a common origin
...
In terms of the planet humans are very young and new
According to molecular cladistics we are the third chimpanzee – Ardipithecus was a chimp/human
ancestor 4
...
2 Mark viney)
-

Evolution = the transformation of animals, plants, and other living organisms into different forms by
the accumulation of changes over successive generation (Oxford dictionary)
Genotype = the genetic constitution of an organism (oxford dictionary)
22 autosomes from each parent forming homologous chromosome pairs and sex chromosomes ( X or
Y) 6400 x 10^6 base pairs in humans (diploid genome) and between 20,000-25,000 genes
...
) and phenotypes
can change over time (e
...
, hair greying)

-

-

-

-

-

Discrete characters don’t have to be binary, and they don’t have to be equally represented in the
population
...
Antagonistic pleiotropy is the idea that the multiple
effects of a gene could be antagonistic in their effect – ageing which is beneficial in early life but
harmful in later life
One trait, many genes
Different genotypes vary I how they respond to the environment phenotype plasticity depending on
environment
Example = Human BMI is increasing which could have an environmental cause (an easier availability
to quick calories and having more sedimentary jobs)
...

The central dogma proposed by Francis Crick- the unidirectional flow of information from genotype to
phenotype (DNA to RNA to proteins) Changes in proteins cannot affect the DNA (shows how
Lamarck’s theory of evolution is wrong as he believed physical characteristics acquired during an
individual’s lifetime e
...
- muscle mass must be passed on through DNA to progeny) not everything in
central dogma is correct – for example epigenetic inheritance which means things outside of DNA
have power to affect phenotype and are inherited these are referred to as transgenerational effects
they are inherited chemical changes to the DNA - e
...
methylation and histones which turn on/off
gene expression
...
g
...
3 Mark viney)
-

-

Sources of change include mutation changing DNA and the recombination of alleles during meiosis
Substitution, duplication, and deletion of base pairs
Transition (A turns into G) when bases change from a purine to the other purine or a pyrimidine to
another pyrimidine- the most common mutation with small phenotypic consequence
Transversion (A turns into T) when bases change from a purine to a pyrimidine or a pyrimidine to a
purine – has a larger phenotypic consequence
Cytosine and thymine are pyrimidines, guanine and adenine are purines
Substitution, duplication, and deletion are caused by errors in copying DNA before cell division- the
proof reading is imperfect, so errors do occur
Mutations can have a small, large or no effect at all it can either be advantageous or deleterious
meaning either a loss or gain of function experience sometimes may be lethal it all depends on the
precision and where the mutation is
...

Synonymous (silent)mutations result in no change, nonsynonymous (missense) mutations change
amino acid sequence
Synonymous mutations are neutral for natural selection whereas non-synonymous mutations are
subject to selection
Only mutations in the germline are inherited- the cells that give rise to gametes (egg/sperm)
Accumulate somatic tissue mutations with age like cancer
...
000 UK births per year
4
...
76% originate from father as more gametes produced
by father – rate of mutation in children increases in parental age

-

-

-

External agents like radiation and UV can cause mutations too
Larger-scale chromosome effects also caused by errors during cell division- deletion, duplication,
inversion, translocation
...
Deletion results in loss of genes,
duplication means double expression, there will also be errors in mitosis and meiotic recombination
which are associated with some human diseases
Humans are diploid own 2 copies of each autosome meaning we have 2 alleles at a locus, errors in cell
division can alter thus e
...
, downs syndrome which is the trisomy of chromosome 21
...
Females are mosaic for inactivated for X
chromosome

Transmission of the genotype and consequences for the phenotype: (1
...
Produces 4 cells,
homologous chromosomes pair which there is a recombination between homologues
...
This zygote then grows via mitosis
...
Interphase DNA already replicated so each chromosome has a sister chromatid
attached at centromere
...
During the cross over chiasmata are formed which hold together the homologous
chromosomes
...
Anaphase 1
sister homologous pairs are separated and pulled to opposite ends of the cell due to kinetochore
microtubules shortening
...
Prophase 2 after a brief interphase new spindles form in each cell
...
kinetochore microtubules from opposite poles of the cell attach to each sister
chromatid
...
Telophase 2 nuclear membranes reform around 4 clusters of chromosomes
cytokinesis results in 4 genetically different haploid cells due to crossing over and random assortment
of chromosomes
...
strong natural selection acting on one phenotypic
trait controlled by one locus means the alleles at that locus will increase in frequency in the
population, therefore its linked alleles will also increase in frequency
In sexually reproducing species the whole unchanged parental genotype isn’t transmitted it’s a
recombined half by each parent that is inherited
Agametic (without gametes) organisms undergo budding or fission, offspring genetically identical as it
is a mitotic process
...


-

-

Mitochondria and chloroplasts are ancient prokaryotic symbionts both with their own circular
genome which is cytoplasmically inherited
Hardy Weinberg equations = p^2 + 2pq + q^2 = 1 (genotypes) p + q = 1 (alleles)
Allele frequencies increase due to natural selection of the phenotypic consequence of the allele,
linkage, or genetic drift
...

Heritability = the amount of variance in a trait that is attributable to genetic effects often tested
through twin studies- compare between MZ and DZ twins
Genome wide association studies have large samples and measure phenotype and use naturally
occurring genetic variants, aim to seek associations between variants and phenotype

Evolution of genes and genomes: (1
...

Genomes are dynamic – they evolve
When species become reproductively isolated genomes and chromosomes diverge
Vertebrate genomes have evolved by whole genome duplication
Gene evolution, genes duplicate and be recycled meaning they can evolutionarily and functionally
diverge (their affect on the phenotype changes)
Orthologous genes share a common ancestor but have separated with speciation
Paralogous genes are descendants of a duplicated gene within a species
Mobile genetic elements are DNA that move around the genome, also called transposable elements/
transposons
...
They can
jump into (transpose) into a gene and cause a mutation
...
7kilo bases long
...
Lot smaller 100-700 base pairs long
...
Euploid changes are when the number of complete sets of chromosomes changes
(2n to 3n)
...
g 46 to 47 –
Down’s Syndrome)
Animals and plants can speciate by changing ploidy and becoming polyploid (possessing more than
two complete sets of chromosomes – 2n)
...
Allopolyploid, chromosomes from different species coming
together and fusing genomes
...
6 Greg Hurst)
-

-

-

If variation exists in a population, some of which is heritable, some variants must survive better than
others then natural selection can occur
...
Eventually the
entire population is identical with the ‘best variant’ meaning there is nothing now for selection to act
on
...

Mutation and Mendel solve the genetic variance problem as mutation generates variation and
segregation maintains variation
...


-

-

Sometimes macromutation are key (e
...
, endosymbiosis- a bacterial cell engulfed by archaeal cell to
start the origins of eukaryotes or polyploidy events where whole genomes double)
...

The modern synthesis, Darwinian evolution theories in the light of our modern-day knowledge of
genetics

Altruism and the precision of adaptation: (1
...
Altruism could be
compatible with the idea of competitive struggle if they are helping relatives to survive/reproduce, or
actions have a deferred advantage
...

Hamilton’s rules: fitness benefits can be gained directly through producing and raising own offspring r
indirectly through helping to raise offspring of related individuals (kin selection)
...

Not all altruism involves relatives…
...
Population size limits mutation which is the main drive for genetic variation (therefore if
we reduce population size of something we can prevent it from developing resistance)
...
g
...


Genetic variation, and why we aren’t all the same (1
...
If you sequence the genomes of 100 people and look for variants we
would find one variant every 300 bases
...

Deleterious mutation ( reduce fitness), neutral mutation ( doesn’t effect fitness), beneficial/adaptive
mutation ( increase fitness)
A mutation event occurs that is a frameshift within a protein sequence, this mutation is deleterious
A mutation event occurs in the third base of a codon and does not change the amino acid encoded,
this mutation is neutral
Mutation increase the expression of a gene, beneficial mutation
...
99% of DNA changes do not affect gene
expression, therefore they have no phenotype
...
Drift
therefore causes loss of variation in small populations compared to large ones
Genetic diversity at neutral variants is therefore highest In large populations
...


➢
➢
➢
➢

Mutational meltdown……
...

Adaptation: is the adjustment of organisms to their environment in order to improve their chances at
survival in that environment
...

CHEETAH CASE STUDY:

Sexual selection and the natural history of sex (1
...
FOR SURVIVAL
Sexual selection: mode of natural selection, preference by one sex for certain characteristics in the
other sex e
...
long tails in birds
...
There is a variation in phenotype
...
some of this variation is
heritable
...
The phenotype is associated with ability to secure mates
...

Varies with mating systems: Monogamy: little capacity for sexual selection
...
Polyandry( many male partners): Lots
...

Intersexual female choice: Females choose males on basis of phenotype
Intrasexual ‘male-male competition’: male compete for access to females
...
g
...

Where sexual selection is strong, males die young e
...
Deer’s, sexual selection like this is in opposition
to natural selection
...
Sperm competition GEOFF PARKER
...


Female choice and sexual conflict: (1
...
g
...

Where males cannot physically monopolize access to females

➢ What do females choose: Arbitrary, direct benefits( food, territory), genetic benefits
...
Zebra finch don’t usually have bright legs band
...
E
...
in insects females will mate with
males that provide nuptial gifts ( food)
...


➢ Indirect (genetic benefits): exaggerated traits e
...
birds with long tails, are a way of telling males with
➢
➢
➢
➢

➢
➢

good genes from bad, represent honest signals of quality
...

Summary: female choice widespread, most female choice associated with direct benefits, some
female choices about genetic quality, human mate choice hard to study
...
Females may wish to re-mate to find a mate which is better;
current male prefers they do not
...
Male adaptation to manipulate female ( to mate with him, not remate with
rivals)
...
The forces
are strong and continuous = reproductive systems being incredibly diverse

➢
➢
What is a species: (1
...
In nature there’s discontinuity, some species are
related but separated
...

Mayr’s biological species concept- species can be defined as populations of individuals that can
interbreed with other members of the same population but cannot produce viable offspring with
members of other species
...

Pre-zygotic and post-zygotic barriers are either before or after fertilization and create genetic
isolation
...

Post-zygotic isolation involves reducing hybrid fertility meaning the offspring is sterile and reducing
hybrid viability meaning the offspring die
...
New species form by
speciation, in which an ancestral population splits into two or more genetically distinct descendant
populations
...


Macroevolution: speciation(1
...

Genetic isolation:
Reproductive isolation: The barriers that create genetic isolation by impeding gene flow
Prezygotic isolation: A barrier where the
Postzygotic isolation:
In allopatric speciation, groups from an ancestral population evolve into separate species due to a
period of geographical separation
...
Common examples of these barriers include mountain ranges, oceans, and even large rivers
In sympatric speciation, groups from the same ancestral population evolve into separate species
without any geographical separation
...
An
example of vicariance is the separation of marine creatures on either side of Central America when
the Isthmus of Panama closed about 3 million years ago, creating a land bridge between North and
South America
...
Generation of many species from one in short period of time, associated with
adaption to different niches
...
g
...
Adaptive radiation occurs in a new habitat and
when they’re isolated
...
Speciation
occurs when a group within a species separates from other members of its species and develops its
own unique characteristics
...

Speciation is an emergent property of isolation and divergence
...
10 Greg Hurst):

➢

➢
➢
➢

Why do we want to know the history of life: It tells us if particular lifestyles evolved repeatedly, it tells
us where pathogens emerged from ( which we may then try and prevent) we know which species
they come from and can prevent things such as trade of certain animals with the pathogens
...

Phylogenetic trees are now more usually DNA based, however they were more anatomy, physiologybased
...
Analogous rather than homologous structures
...

Timing, when things lived in the past: Fossils: preserved remains, Recent material: permafrost, ice,
caves, peat…
...

Fossils can be dated relative to one another by noting their positions in layers of rocks, known as
strata
...

Three reasons we study phylogeny: interest ( related to chimps) , transitions, emergence
Shared derived character: A character that two species share because of common descent; e
...
hair in
mammals
...
g
...

3 ways to date events:
Molecular clock: even rate of substitutions in DNA sequence over time = divergence allows time to
common ancestor to be estimated: good for old divergence, bit less accurate for very recent
divergence
...
Use up to c
...
248x10^4
...
ROCKS and fossils
Relate case studies linking fossil form to biology; dentition, sharp teeth for their diet e
...
cranium and
cognitive function
Conditions under which aDNA ( ancient DNA) is preseverd and the time over which DNA sequence
can be recovered: Cold , dry ( enzymes which break down DNA need water) ; up to 1 million years
What has aDNA told us about human origins? History of peoples, neanderthal biology, neanderthalhumans interaction; Denisovians
Hadrocodium: first mammal to evolve among dinosaurs , 220Mya
Mya:
Resurection genetics and its two potential forms: bringing extinct forms back to life…… bring parts of
the phenotype back e
...
hair, adiposity( storing fat)
Is resurrection biology a good idea?:

Reconstructing the biology of extinct animals (1
...
By looking at footprints we can deduce running speed, movement, pace
...


➢

➢
➢

➢

➢
➢

aDNA = ancient DNA, DNA can be preserved in the dry and cold
...
(Alas this does not actually work in amber as portrayed in
Jurassic Park)
...

Deeper in time to hominids such as Neanderthals who we have nearly complete genomes of so we
can infer their past biology
...
Share mutations with homo
sapiens for language complexity and the ability to taste bitter
...
aDNA provides direct evidence that Neanderthals and Denisovans
interbred to produce hybrids
...

We can obtain sequences from past forms such as a mammoth and use synthetic biology to recreate
whole genomes or take important bits of said sequence and use CRISPR-Cas to transfer it into an
extant relative – like an elephant (De-extinction)
...


Biodiversity on earth (1
...
Increased
oxygenation by 15% allowing aerobic life in large organisms, many of these creatures are not seen
today
...
Rudimentary vertebrae + well defined head +
tail
...

Life on land: plants- derived from green algae, 460 mya spores of bryophyte(moss)
...
270mya evolution of true leaves
...

Animals on land: 480mya fresh water arthropods
...

325mya dominant flying megafauna, massive wingspan – these organism were so big due to the
carboniferous which supplied great amounts of oxygen which means metabolism was extremely
sufficient
...
100mya
...
Amniotic egg ( egg that is on land as it
can now retain water and allow gas exchange)
...
Alteration in
excretion- uric acid
220mya mammals: derived from synapsids ( non-dinosaur reptiles)
160mya birds: derived from therapods, bipedal dinosaurs that commonly had feathers
...
5mya extinction of dinosaurs, expansion of mammals
...
11 Greg Hurst):
➢
➢
➢

➢

➢

➢

Darwin saw evolution as a gradual accumulation of changes over long periods of time
...

Darwin and gradualism = evolution progresses gradually, accumulation of small changes over a long
period of time results in large differences, he was wrong about macroevolution
Whereas Eldredge and Gould’s punctuated equilibria theory suggests from fossil records that species
histories are characterized by long periods of stasis with sudden changes into new forms
...
Continental movement alters climate as ocean/land interface impacts on climate
whereas the center of continent s commonly arid, changes number of shallow seas
...
Taxa are split apart (vicariance)
...
41% of south American mammals have evolutionary
origin in the north
...
Mass extinctions don’t hit evenly
...
Megafaunas are more likely to go
extinct too due to low reproductive rates, slow maturation and low population densities meaning
they recover very slowly from periods of high mortality or habitat fragmentation
...

3) biological innovations= evolutionary novelty alters balance in forms, amphibia were dominant until
the reptile form evolved and flying insects were dominant until birds
...
13/1
...

2
...

4
...

6
...

8
...

Independent replicators –> chromosomes
...

Prokaryotes –> eukaryotes
...

Protists –> multicellularity
...

Primate societies –> Human societies with language
...
Not major phenotypic transitions
...
These
transitions increased fitness
...

Transition 1 ( replicating molecules -> molecules in compartments): Self replicating molecules in
the first instance of life, thought to be RNA which is also catalytic (facilitate chemical reactions) ,
initially individual free “floating” molecules
...

Protects the replicating molecules
...
Keeps
together mutually beneficial RNA molecules
...

Transition 2 ( independent replicator -> chromosomes): independent replicating molecules (
transition 1) = genes……
...

Chromosomes are slower to replicate
...
Theoretically, chromosomes selected for when combinations of genes are needed for

➢

➢
➢

➢
➢
➢

➢
➢

➢

➢

➢

cell reproduction, advantageous when bringing genes together
...

Transition 3 ( RNA as gene & enzyme -> DNA & protein ) : transition from RNA to a genetic code
...

Disadvantage: need to evolve a translation system, translate the DNA into proteins
...

Transcription unwinds the DNA into mRNA, we then translate this mRNA into a polypeptide (
protein) this is done with the ribosome and ribosomal RNA
...
The tRNA:AA
association in translation is a relic of this ancient cofactor biology
...

Cofactor: A cofactor is a non-protein chemical compound that is required for an enzyme's activity
as a catalyst
...
Nucleus contains more than one chromosome
Multicellular Has two membranes: plasma and nuclear membrane
Diploid and haploid
Produce sexually and asexually
...

Cytoskeleton, maintains cell shape, internal membranes (nuclear), linear chromosome in
nucleus
Prokaryote: Nucleus is absent, nuclear material lies in the cytoplasm and is called a nucleoid
which has one chromosome
Has a single membrane surrounding the cell
...

Rigid outer cell wall, no internal membranes, single circular chromosome
...

Why was the cell wall lost? (hypothesis): Competitors evolved antibiotic ( which interfere with
cell wall synthesis)
...
All of life is competitive in many
aspects between all organisms
...

An advantage is that it allows phagocytosis (engulfing/ingesting particles including
microorganisms
...
This
compartmentalises the cell
...
As the
cell wall is lost NEW mechanisms are needed which lead to the evolution of MITOSIS (how
eukaryotic cells divide
...

Transition 5 (Asexual clones to sexual reproduction): Why do some organisms reproduce
asexually and some sexually? Sexual reproduction = meiosis, recombination, segregation and
syngamy (fusion of two cells)
...
Asexual progenies are
identical to each other and parent
...
Two- fold cost of sex is the argument that an individual reproducing asexually
can produce twice the number of offspring clones that sexually produced organisms because in

➢

➢

➢

sexual reproduction two individuals share reproduction
...
It is thought multicellularity came about when the products of
cell division remained together, or a cell had multiple nuclei or colonial-living organisms became
more integrated
...
Animal colonies include eusocial insects (ants, bees, wasps, and termites) and groupliving animals (meerkats, lions, and many birds)
...
The difficulty is that selection acts on
individuals so how can colonial living be advantageous- the solutions to this include kin-selected
altruism (the idea that by helping a relative to reproduce one is helping one’s own genes to be
passed on) , mutual benefit from living in a colony and avoiding cheating
Transition 8: Primate societies to human societies with language
...
14 Mark Viney)
...

We are 99% genetically similar to a chimpanzee but clearly not 99% phenotypically similar to them,
why? Small differences between genes can bring about large phenotypic differences
...

Early stages of vertebrate development = the haploid male and female gametes must fuse to form a
diploid zygote (fertilization)
...
The zygote
rapidly divides into many cells with no overall increase in size
...
Cleavage ends with formation of a blastula/blastocyst
which varies in structure among animal embryos
...
Cells from the three
primary germ layers interact in various ways to produce the organs of the body
...


Parasites and the evolution of parasitism (1
...

Parasitism is VERY common
...

Parasitic worm biomass = fish biomass
Parasitic worm biomass > birds (greater than birds)
What animals are parasites? Protozoa: single celled eukaryotes, Plasmodia
Worms: Nematodes, Platyhelminthes, Acanthocephalans
Arthropods: ticks, fleas, lice
Internal parasites: endoparasites
external parasites: ectoparasites

➢
➢

Parasite vs Pathogen ? Parasite : protozoa and metazoa ( worms and arthropods)
Pathogen : bacteria and viruses
Examples of worm parasites: Ascaris spp
...

Pinworms, such as Enterobius lives on rectum of humans
...

Worm: Schistosoma spp, causes bilharzia
...

Hookworms (nematoad): Live in hosts gut, feed on hosts blood, eggs pass out in host faeces, infection
by skin penetrating larvae
...

Hook worm life cycle
1
...
Egg ( pass out of host)
3
...
Infective L3 stage
5
...
Migrates via lungs
7
...

➢ How did nematodes evolve parasitism?
1
...
Eggs
3
...
L2 (dauer)
5
...
L4 ( dauer)
7
...
Evolved into an
infectious larvae stage
...

Evolved to parasite definitive hosts rather than intermediate
...


➢

➢

Surely it is advantageous to not harm ones host but rather continue to exploit it, parasites
evolve to become avirulence
So why are parasites virulence
Kill a host to allow transmission
...

Evolution is happening at the individual level
Different genotypes of parasites are competing for their individual evolutionary fitness
...

Virulence evolution and parasite control
Some therapies reduce how much harm parasites cause to a host
The evolutionary consequence is that parasites could then evolve to be more virulent (but
because of the therapy they still don’t kill their host, which gives them more room for
evolving to become more virulent)
Subsequent removal of the therapy would then leave more virulent parasites in an
unprotected host population
EXAMPLE, experimental anti-malaria vaccines



---