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Chapter 5 Evolution
M13
M13.1 Know that DNA IS UNIVERSAL TO MOST
LIVING THINGS
 DNA is the fundamental chemical of all living
things
 All living CELLS contain DNA
Bacteria only have a single strand but this contains all
of the code required to replicate themselves- single
circular chromosome or plasmids/small loops of
DNA.
 Main role of DNA is to pass on hereditary
characteristics
 Act as the code for the production of other vital
molecules in living things-mainly proteins
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Evolution is one of the main areas of modern
Biology
Involves the transformation of life on earth
from its earliest forms to the vast diversity that
we see today.
Modern theory stems from Charles DarwinOrigin of the Species
The fact that there is actually such diversity of
life today, despite the origin and DNA
similarities is due to mutations
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DNA is said to have been circular in all first
organisms
As organisms got larger the strands broke
and produced several linear strands of
differing lengths
Several starting points existed along the
lengths making replication easier and quicker
DNA got bigger : one because of the number
of genes now needed and also because there
seemed to be developing lots of sections of
DNA which coded for nothing
These “bits “ of DNA that don’t appear to
code for anything, are junk or non coding
bits, called EXONS
When the exons are cut out by the m RNA
they are referred to as INTRONS
 The amount of exons seems to increase with
the complexity of the organisms
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 The packaging of DNA also became more
complex-proteins called HISTONES began
organising the wispy DNA to prevent
tangles during division which could have
proved that more mutations would occur
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M14.1 Understand that organisms have
common features attributable to commonly
shared sequences of DNA.
DNA is the genetic code
this means it is responsible for all features and
inheritable characteristics
Species that have similar features share many
common aspects of their DNA too.
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Evolutionary relationships have been
established on the basis of these structural
similarities- called comparative anatomy
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This means that structures in different
organisms may be used for different functions
but are fundamentally similar-suggesting a
common origin
These are homologous structures
Page 35 of the text shows that bats. Monkeys and
pigs have very similar structures in terms of
their bones in the wings or limbs, suggesting,
scientist believe a common origin
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Comparison of organisms also involves
comparing major organs- heart/lungs
And now DNA:
 this involves looking at the proteins
 Scientist sequence the amino acids in protein
molecules
If these sequences produce proteins, if the
sequences are similar then it is inferred a
common ancestry—again I see this as if it
works, lets just modify, not change it.
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PHYLOGENETIC Trees:
These are diagrams which show evolutionary
relationships based on their amino acid sequences
They use the sequence of a protein called
cytochrome c
This is a protein that is necessary in the respiration
pathways of nearly all living organisms
This protein varies from species to species: with
the degree of similarity indicating the closeness in
evolutionary relationship
Humans and Chimpanzees match at all 104 amino
acid positions
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If you look at the table/diagram on page 36
you will see we vary 9 from a rabbit.13 from a
turtle and 45 from yeast!
Compared with fossil and comparative
anatomy studies, along with amino acid
sequencing, scientist make their valuations as
to who’s related to whom in the Kingdom!
Sometimes the protein molecule of
haemoglobin is used in amino acid sequencing
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14.2 Explain why the greater the similarity
between the sequence of the nucleotides in
their DNA, the more likely it is that the
separation of the two species is recent.
Species that have a recent common ancestor
will usually have similar DNA and protein
sequences
The longer the time that species have been
separated from one another, the more chance
that mutations have occurred and DNA is less
similar
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Remember we said that this way of
determining evolutionary relationships has
been backed up by fossil evidence and
comparative anatomy studies
To be more sure it is better to actually compare
the DNA sequences in order and arrangement
of the nucleotides
This is time consuming & Labour intensive
So……. We use a method called DNA
hybridization
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DNA is heated from two different species to
the point where the complimentary strands
separate from one another
As they cool, the single strands of DNA will
recombine to form the double helix again
As the strands recombine we see how closely
the different species reattach to another
species…closer the match, less time they have
been separated on the evolutionary
relationship stakes
See page 37 -38Text, or 38-39 large text book