Classification

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Classification
selection
evolution
and
Variation, overproduction, natural selection
Evolution
The Darwin-Wallace theory
Species and speciation
Artificial selection
Classification
5 kingdom classification
Round up
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Classification
selection
Variation genetic and environmental
evolution
Genetic variation arises through
Independent assortment of chromosomes during
meiosis
Crossing over of homologous chromosomes during
meiosis prophase I
Allele reshuffling
Random mating between organisms within a species
Random fertilisation of gametes
New allele production
Mutation
These are all changes in the genes that can be
inherited by the offspring
Environmental variation e.g. body mass due to
food availability, do not involve genetic changes
and are thus not passed on to the offspring.
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Classification
selection
Overproduction
evolution
numbers
Populations have the potential for exponential
growth but are normally checked by environmental
pressures or factors.
Biotic factors
e.g. predation, food supply, infection
Abiotic factors
e.g. water supply, soil nutrient levels.
myxomatosis
If the pressure of environmental factors is
sufficiently great the population may fall before
later possibly rising again.
Thus populations may oscillate about a mean over
a period of time.
Denser populations increase the probability of
disease transmission. Why?
Time (months)
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Classification
selection
Overpopulation
evolution
Lemmings
The chart below outlines the lemming population
changes over a decade.
The populations of most species show a far less
spectacular oscillation, but the pattern is
similar more young are produced than can
survive into adulthood.
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Classification
selection
Natural selection e.g. rabbits
evolution
What determines which rabbits will survive the
environmental or selection pressures?





Successful allele
Selection pressure
Alleles
Advantage
Brown (agouti) / white colour
Blends better with background
Fox predation
brown
Long / short ears
Better sound detection
Fox predation
long
Thick / thin tooth enamel
Limiting food
Teeth last longer
thick
Natural selection increases the frequency of
advantageous alleles.
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Classification
selection
Evolution Stabilising and directional selection
evolution
Stabilising selection
New Zealand tuatara no change in 200 million
years
The environment is not changing and only extremes
of the population are selected against

Stabilizing selection Selective pressures select
against the two extremes of a trait. For example,
plant height might be acted on by stabilizing
selection. A plant that is too short may not be
able to compete with other plants for sunlight.
However, extremely tall plants may be more
susceptible to wind damage. Combined, these two
selection pressures select to maintain plants of
medium height.
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Classification
selection
Evolution Stabilising and directional selection
evolution
Directional selection
The environment changes shifting the range of
variation in a particular direction. The
population shift is an adaptation to the new
environment

In directional selection, one extreme of the
trait distribution experiences selection against
it. Thus the population's trait distribution
shifts toward the other extreme and the mean of
the population graph shifts. Using the familiar
example of giraffe necks, there was a selection
pressure against short necks, since individuals
with short necks could not reach as many leaves
on which to feed. As a result, the distribution
of neck length shifted to favour individuals with
long necks.
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Classification
selection
Evolution
evolution
New alleles
New alleles are produced by mutation.
Nearly all mutations are harmful, conferring a
disadvantage on the individual.
Very occasionally advantageous mutations arise,
e.g. here, white coat colour
Hares possessing the allele are more difficult to
see and are less likely to be predated.
They survive to pass the allele on and over many
generations almost all hairs will inherit the
allele.
Such changes in allele frequency are the basis of
evolution
Mountain hare
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Classification
selection
Evolution
evolution
Antibiotic resistance
Some Staphylococcus bacteria produce an enzyme
called penicillinase which renders them immune to
penicillin.
C
Amp
P
1 resistant bacterium can produce 10000000000
descendants in 24 hours under favourable
conditions.
Strep
Tet
Similar antibiotic resistant strains of bacteria
are constantly emerging. The selection pressure
causing this is the presence of the antibiotic.
Petri dish with lawn of Staphylococcus bacteria
and antibiotic discs Which is the most effective
antibiotic against this sample of Staphylococcus?
The more antibiotics are used, the greater the
selection pressure to evolve resistance.
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Classification
selection
Evolution
evolution
Industrial melanism
Peppered moths
During the day the moth rests underneath the
branches of trees and relies on camouflage to
protect it from insect-eating birds
Until 1849 only the speckled variety was
observed. From 1849 (industrial pollution
getting worse) until the late 1960s the black
variety was reported in ever-increasing numbers
Speckled form
A single gene controls appearance. The alleles
are - C black, c speckled
Trees in unpolluted regions often had growths of
speckled lichen. This lichen was killed off in
polluted areas, causing bark to look much blacker
Selection pressure Bird predation. Successful
allele?
Black form
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Classification
selection
Evolution
evolution
Industrial melanism
The advent of clean air acts from the 1960s began
to reduce the level of industrial pollution
Edinburgh
Newcastle
Distribution of the pale and dark forms of the
peppered moth, Biston betularia in the early 60s
Manchester
Birmingham
London
Cardiff
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Classification
selection
Evolution
evolution
Sickle cell anaemia
HS HS Most people die from anaemia before
adulthood
HN HS Most people show no symptoms. Also,
reduces the chance of death during malaria by
about 20x
2 selection pressures on the sickle cell allele
Selection against those who are homozygous
Selection for heterozygous individuals malaria
resistant
The frequency of the HS allele in an area depends
on a balance between these 2 pressures
The malarial parasite, Plasmodium, cannot live in
sickle cells. Thus sickle cell confers immunity
to the carrier.
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Classification
selection
Evolution
evolution
Sickle cell anaemia
The frequency of the HS allele in an area depends
on a balance between Selection FOR (malaria
rersistance in heterozygotes) Selection AGAINST
(death due to anaemia in homozygotes)
There is selection pressure for both alleles to
remain in malaria-affected areas
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Classification
selection
Evolution
evolution
Artificial selection
The application by humans of selection pressures
to populations
For cattle desired features may include
docility, fast growth rates and high milk yields.
Chillingham White Cattle breed. Similar to the
original wild cattle which once roamed the
forests of Britain from earliest times.
Guernseys are bred for the production of large
quantities of fat-rich milk
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Classification
selection
Evolution
evolution
Fossil Evidence
Richard Dawkins explains the evidence for
evolution http//www.youtube.com/watch?vI-QWv_0M
jq0featureplayer_embedded
Fossils show the development of legs from fins
over 20 million years
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Classification
selection
Evolution
evolution
The Darwin-Wallace theory of evolution by natural
selection
Organisms produce more offspring than are needed
to replace the parents
Observation 1
Natural populations tend to remain stable in size
over long periods
Observation 2
Charles Darwin
There is a competition for survival a struggle
for existence
Deduction 1
There is variation amongst individuals of a given
species
Observation 3
The best adapted variants are the fittest and
survive to reproduce
Deduction 2
Alfred Russel Wallace
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Classification
selection
Speciation
evolution
Introduction
The Darwin Wallace theory did not attempt to
explain how new species could arise.
The mechanisms discussed in this unit explain how
new genes / alleles arise by mutation, and how
selection pressures determine the spread of these
through the population
An important question is how did different
species arise?
A species is
A group of organisms with
similar morphological, biochemical, physiological
and behavioural features which can interbreed to
produce fertile offspring, and which are
reproductively isolated from other species.
The feature that really decides whether 2
organisms belong to the same species is their
ability to interbreed successfully
(A problem is that the 2 organisms may be dead,
fossils, the same sex etc!)
How does a new species arise (speciation)? Here
are 2 models
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Classification
selection
Classification
evolution
The study of the classification of organisms is
called
taxonomy.
A key element in classification is the
identification of shared or homologous features
In vertebrates one such feature is the
pentadactyl limb.
frog
bat
reptile
horse
human
Each has the same basic design, suggesting a
shared or common ancestor.
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Classification
selection
Classification
evolution
Species which share many homologous features are
grouped into the same
genus.
e.g. horse, donkeys and zebras all belong to the
genus Equus, probably evolving from what was a
single species along time ago.
Every species is given a 2-word Latin name called
a binomial
Genus Species
e.g. zebra Equus burchelli . Note the italics
(if hand written, underlined)
This classification reflects the evolutionary
history of the zebra and its relationship with
other organisms.
Kingdom Animalia
Phylum Chordata
Class Mammalia
Order Perissodactyla
Family Equidae
Genus Equus
Species burchelli
The evolutionary history of living organisms is
called
phylogeny.
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Classification
selection
Classification - the five kingdoms
evolution
The system was proposed in 1988 by Margulis and
Schwartz.
The kingdoms are Prokaryotae, Proctista, Fungi,
Plantae and Animalia
Prokaryotae
Proctista
Fungi
Plantae
Animalia
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Classification
selection
Classification - the five kingdoms
evolution
Prokaryotae (Prokaryotes)
Escherichia coli. A rod-shapes gram negative
bacterium. Scanning electron microscope
Light micrograph of filamentous cyanobacterium
Cylindrospermum
Generalised bacterial cell
Prokaryotes Eukaryotes







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Classification
selection
Classification - the five kingdoms
evolution
Protoctista
Amoeba . A unicellular heterotrophic proctist.
Some species live in the sea, others in fresh
water. Some are parasites, e.g. causing the
disease amoebic dysentery
Spirogyra. A multicellular photosynthetic
protoctist found in ponds and streams
Fucus vesiculosis. A multicellular
photosynthetic protoctist. A seaweed!
Protoctists are simple eukaryotes. Some are
single cells, others multicellular. Some are
photosynthetic, others heterotrophic.
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Classification
selection
Classification - the five kingdoms
evolution
Fungi
Saccharomyces - yeast cells
Boletus. Growing on leaf litter
Fungal hyphae with inset drawing based on EM
studies.
Light microscopy photo of yeast cells,
Saccharomyces
Some fungi are unicellular, e.g. yeasts. Others
are multicellular containing mycelium composed of
hyphae. They feed heterotrophically, some are
saprophytes, others parasites (athletes foot).
They dont have chlorophyll and although they
have cell walls they are not made from cellulose
(usually chitin)
Different species of Aspergillus growing on a
lemon
Spores of of Aspergillus niger on decaying fruit
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Classification
selection
Classification - the five kingdoms
evolution
Plantae
A fern Polystichium setiferum
A mixture of moss species e.g. Eurhychium
crassinervium
A flowering plant - Ranunculus
Plants are multicellular eukaryotes that feed
using photosynthesis. The kingdom includes
mosses, liverworts, ferns, conifers and flowering
plants. Plants have cell walls containing
cellulose (bacteria have cell walls but not made
of cellulose). Many plant cells have
chloroplasts and often large vacuoles.
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Classification
selection
Classification - the five kingdoms
evolution
Animalia
The common house spider Tegenaria domestica. An
arthropod.
Orang-utan. Pongo pygmaeus. A mammal.
A jellyfish
Animals relatively simple organisms such as worms
as well as more complex ones such as birds.
Their cells do not have cell walls and they dont
contain chloroplasts. They feed heterotrophically
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Classification
AT THE END OF THIS UNIT YOU SHOULD BE ABLE TO
selection
REVIEW
evolution
describe one example of artificial selection
Explain how natural selection may bring about
evolution
explain why variation is important in selection
explain how all organisms can potentially
overproduce
describe the processes that affect allele
frequencies in populations with reference to the
global distribution of malaria and sickle cell
anaemia
explain the role of isolating mechanisms in the
evolution of new species
use the knowledge gained in this section in new
situations or to solve related problems.
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Classification
selection
evolution
PROCTISTA Amoeba
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Classification
selection
evolution
Fungi
Penicillium spores and hyphae
Aspergillus niger spores and hyphae
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Classification
selection
evolution
Fungi
Fungal hypha
Yeast drawing from EM
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Classification
selection
evolution
Migrations In Scandinavia, lemmings become
restless in years when their populations are
high. In the mountainous terrain of Norway, for
example, when lemmings begin to move they tend to
go downhill and get funneled into valleys. The
result is that large numbers eventually reach the
sea or a large lake. They may proceed onto sea or
lake ice or jump into the water, which has given
rise to the popular conception that they are
committing mass suicide to relieve a problem of
overpopulation. The Inuit have no legends about
migrating lemmings and it is difficult to believe
that they would have overlooked such an event,
especially if it occurred repeatedly. Spring
is a time of social upheaval caused by the
environmental changes associated with snow melt,
and the physiological changes associated with
onset of the breeding season.