Well I’m very pleased to be with you this morning and I would like to talk as it was just said on evolution.
Well biological evolution as well as cosmic evolution are very important things and philosophers, some thousands of years back
and people starting to create religions were thinking on where do we come from, where do we go to and what is our environment.
Nowadays we know a lot and it is in the 18th century that, sorry it is in the 19th century, 1860’s, 19th century
that in fact biologists like Gregor Mendel and Charles Darwin observed that individuals belonging to a particular species,
not always had the same phenotype.
And that was Mendel’s work, that some of these phenotypes got transferred into progeny,
the first one, second one, third one and so on.
That was the start of genetics.
And more or less at the same time Charles Darwin reflected on his observations which he made
that in some geographically isolated areas living beings populations belonging to a species
which was also found elsewhere had in general another phenotype.
So he reflected that natural selection favoured in fact that particular phenotype.
That for example on some island and other phenotypes favoured the development of another variant elsewhere.
One talked on variants and one had at that moment of course no idea as we have now on the basis of genetic information.
What I show here is scheme of neo-Darwinistic evolution which came in the middle of the, around 1940
which was the fusion between classical genetics and evolutionary biology.
You’ll see that genetic variation, I call it now genetic variation rather than phenotypic variation or mutation,
I use these same 2 terms for the same characteristics.
That these drive evolution.
Of course if there would not be any mutation in any of the living beings there couldn’t be an evolution,
couldn’t be a preference and selection.
Now on the other side you see natural selection, this is a complex phenomena
that the way how living beings deal with their encountered environments.
And we do know of course that an environment is composed mainly on physical chemical, non-living matter
and on biological environment.
That means all the other living beings which live together in the same habitat as the one we look at
can exert some selective influence on each other.
We do know that what we do in the laboratory, I’m a microbial geneticist
and I did most of my work with Escherichia coli bacteria, clearly defined, no other living beings around,
in a medium which was a good growth medium.
They had a generation time from 1 cell division to the next of 30 minutes, so everything was fast.
And one could easily see these things.
This is not what happens in nature, even in my body, I know now that not only me
but you all carry at least as many microbial cells in your body as human cells.
And you are not feeling sick by that, they help you actually in your life, we help them, we give them,
provide them as a host the possibility.
So we should consider – and this is quite important for medicine also – consider any living being higher organisms,
being it human beings, animals or plants, as in fact ecosystems with a multitude of different kind of organisms which cohabitate.
Then the rest is isolation, I mentioned already Charles Darwin’s observation
that on isolated islands maybe that influences the biological evolution.
So the general conclusion which you see here is without variation there wouldn’t be any evolution.
So genetic variation is the driving force of genetic evolution on biological evolution.
Natural selection, together with at any time available genetic variants
and the parental forms decide where the branches on the tree on evolution are growing.
That means the directions of evolution.
And isolation of course modulates the process.
The question is what are now the genetic variations, how do these variations occur.
In many text books still nowadays you see that in the DNA these are errors of replication or accidents happening to the DNA.
I wanted to invite you to give up that idea, it’s a wrong way of understanding nature.
That the process of evolution is so important and you shouldn’t accept that this is based on errors.
We will see how that works.
And in order to see how that works we have to think how do we investigate that.
On the lower part here in red I say individual processes of the generation of genetic variants should be studied case by case.
And of course with animals or human beings that’s very difficult because of the very long generation time,
on the very long genome.
You do much better if you study that with bacteria or even with viruses.
And I wanted to report to you results which were mainly obtained originally with microbial genetics.
However since about 2 decades we have more and more nucleotide sequences available, these are entire genomes
but you could also be interested to look in individual genes
or even in a small domain on a gene which is homologous in other genes.
And you could see groups of genes which sometimes collaborate with each other.
And that can be easily done, this kind of comparison of nucleotide sequences by bio-informatic tools.
So that’s also quite efficient.
It doesn’t show how the process occurs but it can validate what you conclude from microbial genetics
and that is quite beneficial.
Now the E-coli bacteria have interestingly just one single circular DNA molecule as a genome
which is almost carrying almost 5 million base pairs.
And the genes of course we all know that it’s few decades which are coding for gene products which often are enzymes.
These are mainly proteins, sometimes also RNA molecules.
And of course genes have expression control signals which are located at different sites
on which other proteins may interact, RNA may interact.
And if you now consider a mutation, not any longer as a change in the phenotype but change in the nucleotide sequence,
it becomes obvious that if you have a mutation within the reading frame of a gene,
you may or may not have an alteration in the gene product.
And if you have mutation in the expression control signal you may or may not have a different availability of that gene product.
With that knowledge let me just see, I said may or may not, why, because it became clear
and I think most of the biologists are in consent with that idea, that mutations,
novel mutations are only relatively rarely favourable, that means useful for the individual which suffered the mutation.
And providing a selective advantage in the encountered environment.
Much more often novel mutation is unfavourable, providing selective disadvantage
which can inhibit the life processes, sometimes very strongly so that in growing bacteria, dying bacteria, it’s just lethal.
But many other mutants have no immediate influence on life processes, they are called silent and neutral
and these may or may not at some later time together with additional novel mutations have some effect on the future evolution.
And we do know several reasons why some of the mutations are silent.
Under these conditions with rarely favourable mutants occurring spontaneously
we can conclude that we indeed have no good evidence for a directedness of spontaneous mutations.
My bacteria have no sensors to find out, oh I’m now in another environment,
I should change this particular gene in this particular way in order to ferment,
for example a sugar which was not present before.
That doesn’t happen.
It’s more random, by chance rarely this mutation, maybe in one cell or a few cells of the population
and then it becomes selectively favoured and can eventually overgrow the rest of the population.
And for the same reasons tolerable mutation frequencies in my haploid organisms
and you can extrapolate to do this to diploids also must be very low,
you don’t want per generation to accumulate many, many novel mutations in the genome because many are actually detrimental.
So we will have to see for ways how mutations occur and how nature manages to keep evolution rates at low levels
in order to tolerate life of a majority of the individuals in populations.
What you see here again is on the right hand side, the sources of genetic variation, that means genetic variation,
we have isolation there and natural selection.
But I now comment on the processes of genetic variation.
We do see that there are more than one, actually quite a number of different specific mechanisms
contributing to the overall genetic variation in the microbial populations.
And some of these occur during DNA replication, some of these are due to rearrangement intragenomically.
A part, a segment of that linear genome can be duplicated, can be deleted,
can be inverted and remaining at the same site, can transpose from one site to another and so on.
And these processes, all of these processes are experimentally explored
and we do know at least in some of them how nature manages to keep the rate at very low rates of these occurrences.
Finally there is also, it is also known that sometimes a gene or a group of genes or even functional domain
only can find its way from one type of organism into another type.
And then we will see how that can behave there and exert some influence.
So you see there are a number of different mechanisms and it is interesting
to know that if you study for example E-coli strains and then you compare with some other bacteria
you see that the specific mechanisms in these living beings are not always absolutely the same.
There may be other genes there.
But it is important to have such genes which help evolution and I will comment on those just in a moment.
Before going you can see in fact you can attribute any of these observed specific mechanism
to what I call natural strategy of genetic variation.
And I can identify 3 strategies, one is a local sequence change, the other is a DNA rearrangement
and the third one is DNA acquisition.
So I go back to that, here we already said E-coli has a genome of about 5 million base pairs.
If we compare that with our written language, where we put one letter after the next,
the local sequence change is corresponding to changes within one word.
You delete one letter in the word, you insert another one or you mingle up the sequences.
And these are very local changes.
The second one, you take a segment, maybe half a page which you duplicate and leave there
so that the further evolution can work on one without changing the other one.
Or you can invert that segment and so on.
And the third strategy you take one page for example or part of a page from one organism of a different type
and you bring it over into an organism which will be then the recipient organism.
That’s horizontal transfer.
I will come back at the very end, shortly to comment on this once more.
By the way the bible, old and new testament have not quite, in the German edition,
not quite 5 million letters, so E-coli is a book of the size of the bible.
We human beings have about 700 times more, that means an encyclopaedia of about 700 volumes.
And there are even living beings, including plants which go up to 1000 of these books in their genetic library.
I want now to comment just very briefly without,
I’m sorry in 30 minutes I cannot give you existing evidence for this what I say,
but what you see here is what Watson and Crick already commented on in the Cold Spring Harbour Symposium of 1953.
That in fact it was known from organic chemistry since quite some time
that isomeric forms exist from organic chemical compounds and that also applies to nucleotides
and the adenine which normally pairs with thymine.
In fact has a most stable form but a short living tautomeric form
in which one hydrogen atom is found not on the same place as in the standard form but slightly near to another nitrogen.
That influences of course the 3-dimensional configuration of that molecule
and it cannot pair any longer spontaneously with thymine.
But interestingly Watson Crick already mentioned that time, it could in principle pair with cytosine.
So then when the short living tautomeric form shifts back to the standard you have a mis-pairing.
So mis-pairings of course if you reflect shouldn’t be attributed to errors,
nature uses this kind of structural flexibility of bioorganic molecules to do something rarely.
It doesn’t make it, during replication on long molecules of DNA, perhaps only a few times.
But the longer the genome is the more that could bring you into problem because most of the nucleotide,
many of the nucleotide changes may be unfavourable.
And we do in the meantime know that in all living beings which have been studied so far,
in fact there are efficient repair systems able to identify these nascent mis-pairings very rapidly.
These enzymes largely, not quite all but largely can identify which is the parental strand
and which is the newly synthesised strand in which the wrong nucleotide was added for creating afterwards the mis-pairing.
And they can repair that.
Without that I think life of higher organisms wouldn’t be possible, even for bacteria.
So that's a wonderful thing.
And the repair is not absolutely 100%, if a repair would be 100% you wouldn’t have local,
this type of local nucleotide substitution which is an important contribution to biological evolution.
So I think in the course of long past evolution these repair systems have been fine tuned to do their work
so that those living beings which are among us, including us,
in fact profit from having the possibility to do that work in order to keep local mutagenesis very low.
There are other local mutants, for example local mutagenesis can also be due to the effect of chemical mutagens and so on.
But I have no time to go into all these details.
Rather I want to remind you that already in E-coli bacteria there are several systems of genetic recombination.
All enzyme mediated.
One is homologous recombination which is also called general recombination between sequence homologies
which may occur at different places of a certain length.
It has been shown also that transposable genetic, mobile genetic elements are carried,
various types of such elements are carried in the genome.
These have the size in general of a gene of about 1,000 nucleotides
and if more than one copy is in the same genome of course they can also serve for rearrangement
for making duplications by general recombination for inverting the DNA in between the site of these 2 identical mobile elements.
Transposition per se, of course it’s called transposition because enzyme driven,
they have their own enzymes which are called transposase, they are expressed at very low rates, all of that is controlled.
Most of the cells have no enzymes for these but once in a while this enzyme,
a few of these enzyme molecules may be synthesised, one may carry out the transposition
and transposition is taking an element, putting it elsewhere, sometimes copying an element
and putting the new copy elsewhere and so on and so forth.
Not all of these elements work really absolutely the same way.
And the third strategy is looking for so-called specific nucleotide sequences,
these must be largely homologous, actually we call them consensus sequences.
Experiments which we have carried out in our lab had these sequences of a length of 26 base pairs.
And it was seen that these work relatively efficiently and reproducibly.
So flip-flop systems which have been described are systems which any 1 or 2 generation,
a segment of DNA just gets inverted and after another 1 or 2 back and so.
So if none of the 2 orientations is lethal of course the bacteria can well survive.
And sometimes it occurs that the site of recombination is within reading frames and you have fusion of reading frames
when you make that and if one or even more identically 2 are of the same type then you get.
I see I’m a bit on the long side, I will speed up.
Because I wanted to say a few more words.
This is classical microbial genetics, transformation, conjugation and viruses contribute to horizontal gene transfer.
Gene transfer is considerably limited by various factors including restriction modification systems
and these are also enzymatically guided.
And because of the horizontal gene transfer, in fact I have no T-shirt for that
but you should probably think about also occasionally make a horizontal connector between some of the trees
because of allowing single genes or part of genes or small group of genes to transfer from one branch to the other
and that enriches.
Charles Darwin had said living beings have common origins and now we can say that’s still correct
but also present living organisms have a common future
because we don’t know when our progeny will profit from a horizontal transfer of genes which were developed elsewhere.
And this brings me, what is the qualitative difference between these different genes.
I just said that horizontal transfer, you may at some occasion acquire a foreign gene,
that sharing in successful developments made by others and by just one step of horizontal transfer.
Like for example if bacteria were antibiotic resistant, you may enormously profit from what others have developed in past times.
DNA rearrangements, I mentioned that gene fusions can occur,
operon fusion is fusion of a reading frame with an alternative expression control signal.
And finally the local sequence changes is an improvement, possible improvement of available biological functions.
And the molecular clock which is helping to see evolutionary times and differences is still valid
but it applies only to local sequence changes.
While the 2 other natural strategies could perhaps sometimes offer explanations for the emergency of novel properties
which evolutionary biologists always wondered how they could come about.
And I mentioned genes, recombination genes, these are variation generators.
I mentioned repair enzymes, these are modulators of the frequency of genetic variations, so are restriction enzymes,
they keep the rate of horizontal transfer between unrelated organisms relatively low, but not zero.
And always non-genetic elements contribute.
I mentioned the structural flexibility of nucleotides, that can be generalised probably to other reactions.
Then random encounter for example the effect of the environmental mutagen or being infected by gene vector,
bringing in a gene from another kind of organism and so on.
Natural reality, that’s a conclusion, natural reality takes actively care of biological evolution.
Because of these evolution genes we have to realise that in our genomes as well as in E-coli genome
there are 2 kinds of genes, genes to the benefit of my own life, for the fulfilment of my life
and other genes which in fact work for the evolution, expansion of life and they are the sources of biodiversity.
Just a few words.
I mentioned before these libraries.
And in genetic engineering recombinant DNA techniques can be serving to study particular genes,
for example if you have an organism which is under study you mutate a particular segment of the DNA.
For example by making a local sequence change or by deleting the whole segment, bringing it back,
the changed DNA into the living being.
And looking for changing in phenotype, you often can conclude
of what a particular part of the genome is actually good for in functions.
Or alternatively you can take from a donor cell a small part, half a page or a page
and insert it into a cell which is under your study or you want to use for production of that particular product.
And this, if you see this critically, you see that the strategies in genetic engineering are just very, very similar
to natural strategies which have always occurred in living beings since a long time.
And therefore we can predict that risks, even long-term risks of genetic engineering
are of the similar magnitude as long-term risk of natural biological evolution
as well as on the classical breeding of plants and animals.
That means this risks are very low because we know from long periods of observation
that in nature these risks are really quite minute if not completely zero.
And that allows you to see how that gives an advance and that's my last conclusion,
for any type of biotechnology classically you looked into nature, you found something
and you had to use that particular organism to use it to produce it.
Insulin had to be taken from animals or ideally from human beings,
if possible from very closely related animals, that’s not any longer needed.
You can take that insulin gene from good human being, insert it into another kind of living being,
being it a micro-organism, grow it up and harvest the product.
If you want you could also improve by site-directed mutagenesis,
that particular product before inducing into an appropriate organism.
And this is a possibility which comes from the conclusion of biological evolution.
Sorry I couldn’t give you any detailed really data but in the literature
you’ll find for all what I said really solid background information.
Thank you for your attention.
(applause).