Transcript how closely related 2009

WHEN DID EVOLUTION
CAUSE SPECIES TO
DIVERGE?
Evolution & Homeostasis
2011
Phylogeny
• Over time, scientists have used different methods to
determine how similar different organisms are to each
other.
• This is used to construct cladograms (also called
phylogenetic trees), which show which organisms evolved
from common ancestors, and when.
• Cladograms can be constructed using various
characteristics
• Structural similarities- anatomy & physiology
• DNA hybridisation
• DNA sequences
• Protein sequences
• Immunoglobulins
• Mitochondrial DNA
• The cladogram may be different depending on which
characteristic is used
Biochemical evidence
• The more differences between the DNA or proteins of two
species, the more distantly related they are, and the further
back in the past their ancestors diverged.
DNA hybridisation
1.
2.
3.
4.
5.
DNA is extracted from cells from 2 different species.
The DNA is cut into fragments with enzymes.
DNA is heated so that the 2 complementary strands
separate.
Strands from the 2 different species are hybridised
together, but in some places the sequence is different so
there are mismatches.
The number of mismatches can be calculated by
measuring the temperature required to separate the
strands- the more mismatches, the lower the temperature
required.
DNA sequencing
• Now molecular
biology &
computers can
be used to find
& compare DNA
sequences
directly.
Comparisons of the bhaemoglobin gene
Mitochondrial DNA
• Mitochondria contain their own
DNA, separate & different from the
cell’s genomic DNA.
• mtDNA is only passed down from
the mother.
• Hence it is possible to determine
the maternal lineage.
mtDNA as an evolutionary clock
• mtDNA mutates at a known rate.
• Hence differences in the sequence of mtDNA can be
used to determine when species diverged.
• Fewer differences between species indicates that they have a
recent common ancestor.
• More differences indicates that the species diverged earlier in their
evolutionary history.
Protein evidence
• Studies of the amino
acid sequence of
proteins such as the
globin family
(myoglobin/
haemoglobin) show
how long ago species
diverged from a
common ancestor.
Immunoglobulin evidence
• Relationships between living species can be determined
by studying reactions between antibodies from one
species & proteins from other species.
• Example:
• Protein from a human is injected into a rabbit.
• The rabbit produces antibodies against the human protein.
• Blood is taken from the rabbit, and the serum containing antibodies is
separated from the blood (anti-human serum).
• If the human protein is added to the serum, antibodies bind to the protein
& a white precipitate forms.
• If chimpanzee protein is added to the rabbit
serum, only some of the antibodies
recognise the protein enough for some
precipitate to form.
• The more distantly related the species are
from humans, the more dissimilar the
proteins are, and fewer antibodies bind to
them.
• Thus a family tree can be built up based on
the structural differences between proteins.