Transcript Darwin`s finches - University of Birmingham

What would we tell Darwin?
H. John Newbury
David Attenborough
Linnaeus and ‘species’
This Swedish biologist established
conventions for the naming of living
organisms.
1707 – 1778
Implicit in his organisation of species
into classes, orders, genera etc was the
concept that some species are more
closely related to each other than others.
Scientists at this time were treating species as fixed
entities and there was not yet a suggestion that one
species could ‘evolve’ into another (or that more closely
related species had more recent common ancestors).
Darwin’s Theory of Evolution
During Darwin’ lifetime, some
biologists were thinking about existing
species being able to change into new
species by a process of ‘evolution’.
(12 February 1809
- 19 April 1882)
Darwin’s real claim to fame is his explanation of the
forces that drive evolution – and, critically, of powerful
role of Natural Selection.
Darwin’s Theory of Evolution
Evolution can be summarised as the inevitable result
of two processes:
1. Random changes in individuals that are
passed on to their offspring.
2. Natural Selection acting on individuals
resulting in the survival of the ‘fittest’.
Darwin’s Theory of Evolution
The result of these processes is that a species can
change its characteristics (evolve) over time.
If some members of a species change and others do
not then this diversification can lead to the
development of two different species (speciation).
What have we found out about this since
Darwin was alive?
The first part of Darwin’s process of evolution involved
random changes in individuals that are passed on to
their offspring.
It is in this area that there have been enormous
advances.
Important initial discoveries during
Darwin’s lifetime
Mendel and
Discovery of
Pasteur and
patterns of
inheritance
chromosomes
the discovery
of bacteria
in eukaryotes
Eukaryotic
genetics
Recognition that DNA is the
genetic material and
elucidation of the genetic code
Gregor Mendel
Gregor Mendel was an Augustinian monk
working in a monastery in Austria. He is
commonly referred to as the Father of Genetics.
He used peas as his model system and looked at
the inheritance of seven different characters. This
involved crossing and selfing and then examining
some 29,000 pea plants.
He developed generalisations which later became
known as Mendel’s Laws of Inheritance.
1822 - 1884
An example of ‘Mendelian inheritance’
Mendel proposed that invisible internal units of information
account for observable traits, and that these "factors" are passed
from one generation to the next.
The character here = seed shape. This can be round or wrinkled.
Round
X
Wrinkled
RR
rr
F1 seeds all round
Rr
selfed
F2 seeds ¾ round, ¼ wrinkled
Discovery of chromosomes
1882 Discovery of chromosomes and mitosis.
1887 Each species has a fixed number
of chromosomes; discovery of
meiosis during egg and sperm
production.
1900 Pairing of homologous
chromosomes during meiosis
1902/3 Egg and sperm receive one chromosome from each
pair from each parent.
Chromosomes
These discoveries were possible because of
improvements in technology: in microscopy and in stains.
Note that the stains bind to the bases (A,
G, C and T) in the DNA in the
chromosomes.
Chromosomes
The discovery that the pattern of inheritance of ‘Mendelian
traits’ was mirrored by the pattern of inheritance of
chromosomes led to the proposal that chromosomes are the
carriers of heredity. i.e. that Mendel's "factors" are located
on chromosomes.
Took some time to become accepted.
Some, like Bateson, rejected the idea.
1861 –1926
DNA, inheritance and Louis
Pasteur
Much later, it was shown that the ‘genes’
(as Mendel’s ‘factors’ had become known)
were regions of DNA within
chromosomes.
1822 –1895
Some of the seminal work that led to the discoveries
about DNA involved bacteria.
Louis Pasteur was responsible for the demonstration
that micro-organisms actually exist.
Pasteur and micro-organisms
He showed that a clear broth would start to ‘ferment’
if one left it open to the air.
If one boiled it and left it sealed, it did not ‘ferment’.
He proposed that micro-organisms were all around us
and that they were responsible for the ‘fermentation’.
This become known as the ‘germ theory (of disease)’:
cf the ‘spontaneous generation’ theory.
Bacteria and the DNA story
DNA is the genetic material
1877 - 1955
Oswald Avery showed that DNA is the
genetic material by demonstrating that it
was transfer of DNA from a virulent to an
avirulent strain of Streptococcus that
transferred the virulence.
Bacteria and the DNA story
The genetic code
The sequence of three
nucleotide bases (a codon)
that tell the cell which of
the 20 amino acids to put
into a protein was initially
determined by using E.
coli cell extracts and
synthetic mRNAs.
BUT the genetic code is
UNIVERSAL
Model organisms in Genetics
So, if Darwin was here today, we
could explain all this new
information about genetics and
DNA.
But what examples could we give that are relevant
to the theory of evolution through natural
selection?
Let us consider one of Darwin’s classic
examples of evolution
‘Darwin’s finches’.
Time line:
These birds were collected by
Darwin when HMS Beagle visited
the Galapagos islands in 1835.
The value of islands in evolutionary studies
Islands represent an isolated environment where there may
originally have been only a few species and there is a low
rate of invasion of new species.
In the Galapagos, the
proposal is that one species
of finch arrived at the islands
and subsequently adapted
into many different species.
Adaptive radiation
The major changes in the Galapagos finches have been in the beak
structure and this has been associated with the ease with which
different food can be accessed.
But has anything been discovered about the
inheritance of beak characters?
Work in various laboratories has
attempted to identify genes controlling
beak shape.
The Grant group from Harvard are
able to spend part of their time in the
field and part in the molecular
genetics laboratory
One of the Grant research
group in the Galapagos
A beak development gene
There is experimental evidence that some genes are involved in
controlling ‘craniofacial’ development in vertebrates: i.e. the
development of the structures in the area in which birds produce
beaks.
One of these is called Bmp4 and there is evidence that it controls
beak width and depth in birds.
Genetic engineering experiment
Chicken embryos were genetically engineered so that
they expressed Bmp4 more strongly.
At a stage before the structure of
the beak can be seen, an extra copy
of the Bmp4 gene was introduced
and strongly expressed in the
‘mesenchyme’ tissue that will
eventually form the base of the
beak.
Result
Embryos with the extra Bmp4 later produced wider and deeper
beaks.
The conclusion of the
authors is that, while other
genes may also contribute
Control
to the control of beak
development, Bmp4 is a
key gene in the evolution
of beak shapes in
Galapagos finches.
Extra
Bmp4
Another gene controls beak length
In a set of parallel experiments, a gene controlling beak
length (a Calmodulin gene) has been found.
Genetically engineering chick embryos expressing the
Calmodulin gene more strongly during beak development
produced longer beaks.
Control
Extra CaM
What other contributions has molecular genetics
made to evolutionary study?
... A P G X I V C C K R L E D ….
The new
‘missing links’
1... A P G M I V C C K R L E D ….
2... A P G M I V C C K R L E D ….
4... A P G K I V C C K R L E D ….
3... A P G M I V C C K R L E D ….
6... A P G K I V C C K R L E D ….
5... A P G K I V C C K R L H D ….
Application of sequence analysis to Darwin’s finches?
Using sequence data from a couple of proteins, one can propose the
evolutionary process that led to today’s surviving species. One can
also suggest the timescales over which these processes occurred.
What could we tell Darwin about recent
work on fossils?
Hell Creek is in Montana and very well-preserved fossils
have been found in the sandstone rock. One of these is
the 68 million year old Tyrannosaurus rex specimen
MOR1125.
Collagen found in fossil bones
If samples of the bones are
demineralised and then examined
using a specialised electron
microscope, fibrous structures can
be seen.
This looks like collagen, which is the
most abundant class of protein found in
bones (>90%).
Analysis of T. rex collagen
The collagen is present at very low concentrations, but
it is possible to obtain fragments of the protein and
identify the amino acids in these fragments.
An example of one of the amino acid content of one of
the fragments:
Gly Leu Pro Gly Glu Ser Gly Ala Val Gly Pro Ala Gly
Pro Ile Gly Ser Arg
Note that collagen has a high glycine content (about
33%) and this it is at the gly residues that it bends to
produce its helical shape.
What living organism has a protein that is most
similar to that in the T. rex bone?
If we go to the BLAST software, we can search the
international databases of DNA and protein sequence
to find out.
BLAST website: http://www.ncbi.nlm.nih.gov/BLAST/Blast.cgi
Amino acid sequence of protein fragment from T. rex.
grpgapgpagargndgatgaagppgptgpagppgfpgavgakxxxxxxxxxgsegpqgvrge
pgppgpagaagpagnpgadgqpgakgangapgiagapgfpgargapgpqgpggapgpkx
xxxxxxxxxxxgdgakgepgpvgiqgppgpageegkrxxxgepgptglpgppgerxxxxxxgf
pgadgvagpkgapgergsvgpagpkgspgeagrpgeaglpgakgltgspgspg
Result
The results show that several modern vertebrates have
collagen sequences quite closely related to dinosaurs.