Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences
at the University of Oxford, and we're right in the middle of this very serious corona virus crisis right
now. And my students are all stuck at home and we want to keep them in touch with biology
and keep in touch with us. And so we're going to make a new series of videos and they're going to be called back garden
biology.
Well, welcome to this week's episode. I'm going to be looking at this flower,
not the primroses underneath, which is where I started this series, but at these purple flowers
that are hovering above them. The primrose is just seated themselves into this bit of lawn.
But I actually planted a little dry, fragile bulbs of these
four artilleries myself. And these are now a few years old and they're thickening up nicely
and they're just growing in the grass and they're quite happy to do that. The proper name is a snake's
head for artillery, and that's the county flower of Oxfordshire. So they're
quite common in Oxfordshire. You find them growing in very wet meadows. This part of the lawn
is quite where to me. I'm pretty happy here, although it's not a proper water meadow. So they're not as fussy
as that sometimes made out to be. The colour is, well, not
everybody's cup of tea. They've often been described as mournful and melancholy. And that
used to be one of their traditional names, the melancholy fairy. They've even described as
Fergus purple colours, not to everyone's taste. If you look inside them, you can see the classic
arrangements of anthers and the stigma in the middle and the bees
like them. So they do get visited by my pollinators. Now, this is the normal
form, the purple form. But if we move sideways a little bit, you'll see
there's a light form there. And in every population of snakes had
fraternities, there are always white ones. Perhaps 10 or even 20 percent of the flowers
are white. Now, that's pretty unusual,
actually. It's not that uncommon to occasionally have a white form of some
plants. But to have it at such a high frequency, to have 10 or 20 percent
of them be white, that requires a special explanation. So we're
trying to understand how the white fertility is able to persist at around one
in 10 individuals. Well, that's my estimate for my own garden. And to understand that, we're
going to have to think about its genetics and to understand that I'm going to start with some Lego.
This is a Lego spaceship from the Star Wars series that my son made. And
we bought him a kit and the kit came with all the bricks inside and an instruction manual.
And here's the instruction manual. And this tells you exactly how to put all the bricks together
so that you can make the starship that you want and organisms, whether they're humans or
fertilises, also have an instruction manual. We can't see it, but it's inside
them and it's inside their cells and we call it a genome. And what's unusual
about the instruction manual, the genomes of most organisms is it's actually doubled up.
So you actually have two copies of the manual that work together seamlessly.
And you've got one copy of the manual from one of your parents and you got the other copy from the other parent.
And that's exactly the same for the fraternities. All right. So you have two copies
of the instruction manual. That means you have two copies of every single instruction. And
the single instructions are called genes. And I want to think about that gene that
makes the purple pigment that makes those flowers purple. So let's focus
in on that. So I'm going to imagine that
this is what the instructions, the genes look like for the purple individual. So they have
two copies of an instruction or a gene that makes that purple pigment
and they have two copies of that one from each parent. Now, sometimes when individuals
are born, there are mistakes in one copy of the manual. Mistakes just arise all the time
we call those mutations. This mutation is called a loss of function
mutation because this gene doesn't work anymore and it can't make the purple
pigment. That might not be too bad for this individual because it still has a copy of the gene
that does allow it to make the purple pigment. So it may look entirely normal. We sometimes call
these individuals carriers that carrying broken genes, but they don't have any visible effect.
But those individuals may be passing on genes, which means that sometimes an individual
is born with two broken copies of a gene and that can be very serious for
that individual. In this case, what it might mean is that the fraternity is white
because neither copy of that gene can make the purple pigment and say that the
flower ends up white. Now, what about the fitness of these individuals? How successful
are they going to be? Well, if the red and the purple white were exactly the same
fitness and that and these ones always looked purple, then we'd actually expect the
white ones to fit around 25 percent. That's a bit too high. I don't think they're quite as common
as that. More like 10, which suggests that the white ones are not quite
as successful as the purple. So that's why push them down a bit. Perhaps they don't produce as many seeds. Perhaps
they don't attract as many pollinators. And if that's true, actually, we would
expect the white one to become really quite rare, because every time there's two copies of the of the
non-functional gene together, that individual doesn't do very well. So those genes are not passed
on. So it's a little bit too high frequency to imagine that this is what's happening.
So the key to this lies in these individuals, in the carriers. So we seem to hear that
they are just as good as the individuals who have two copies. It
may be that they're even worse, that they have a disadvantage, in which case this non-functional
gene will be lost very rapidly from the population. And these individuals will be really rare.
But just sometimes, these Kariya individuals can actually be more
successful than the individuals with two functional copies of the gene. And you may know
the condition in humans called sickle cell anaemia. When this happens, it's
the haemoglobin gene, Notter Purple, which is still a pigment gene, but something that's very important in humans for carrying
oxygen around the body. And if you live in an area with lots of malaria, then having
a normal haemoglobin gene and one sickle cell gene can protect you against malaria,
despite the fact that you get two copies of the break, Gene, you're really in trouble.
And so it's entirely possible, although I have no idea. And I'm just guessing that this is what's
happening with the snakehead fertility. Perhaps those individuals with one functional gene or one
broken gene are actually more successful than those ones. And if they are, then they
would be able to maintain the white fertilises as a higher frequency in the population.
And this is just a general mechanism that can go on. Nobody's studied the flotilla is well enough to know
about what's happening here. Okay, well, we're going to go back outside and
think about a second mechanism that might also maintain those white for tanneries.
The second explanation about why those wait for artilleries are able to persist at quite high
frequency. We need to think hard about what that purple pigment that the purple for terrorism
making really does. And it is a type of pigment called an MFA on.
And most plants produce those. And this Aissa is an example of a plant that's producing it
right now. And I hope you can see that the leaves are not green. These are the brand
new leaves coming out in spring. And they're heavily tinged with reddish purple
colour. And that is caused by ANFO silence. And if you look around your garden
now, lots of plants that are putting out new leaves, whether it's paeonies roses,
they're often very heavily red and purple. They don't really look green at all. Some of them,
why are they producing those pigments which are probably expensive for the plants to produce?
Well, it seems that they have some protective function. They can protect the new leaves against all
kinds of things. Frost, for example, which can happen later in the year unexpectedly,
but also damage by insects and pests, possibly even diseases.
So once we know that, that might help us to understand that patellar is a little bit better. So I'm just
going to go next to those now and have a think about that.
So these purple for Artillery's, the purple colouration is not confined to the flower. I won't
try to zoom in on this too much, but this stems because it's difficult to see. But
the stands are also quite heavily purple. Whereas the white one doesn't
have any of that. So it just can't produce those anthocyanins, it seems.
So the question is that could be a benefit to the white ones. The anthocyanins are expensive
to produce. So if it doesn't produce them, it might actually be more successful than the purple
ones. But that might only work when it's red. Okay.
And if we just take a look at the whole population now, imagine that the purple
ones, because they're producing the signs, are resistant to a pest or a disease
that might sweep through that population. And the white one at the moment, because there's only one
of it can hide amongst these resistant ones. It's benefiting from something
that we call herd immunity. And you might have heard a lot about herd immunity in the context
of the corona virus. Now, the problem for the white one is that, okay, at the moment
it's fine and it might even be doing better than the purple ones. And it's frequency might then increase.
But if it increases to March, you'd have a lot of white ones and only a small number of purple
ones. And the herd immunity is now lost and a disease or a pest might sweep through
that population and kill all the white ones or severely damage them. And so
you get this thing called frequency dependent's. When the white one is rare, it might
have an advantage, but if it becomes too common, it then gets a disadvantage.
And that is a general mechanism that can keep a second type of individual
in a population at a low frequency. And that might be what's going on with these
white fertilises. I honestly don't know because I don't think anyone's studied it carefully enough,
but it's definitely a possibility. So let's look at the population again and just think about that herd
immunity concept, because you're probably hearing a lot about the white vulnerable individual
here can benefit from the herd immunity. Now, we as a population are like we're
like a big population of white for is at the moment. None of us have ever had corona virus. We're
all vulnerable. But as that disease comes through the population and you can imagine
the white fertilises turning purple as people get the disease recover
and become resistant. And that's what we're trying to build in the population. We're hoping
that enough of us get it and recover from it and become resistant, that we
can offer protection to the very vulnerable to the white fatalities amongst us who
perhaps just aren't are so vulnerable, because if they got it, it'd be so dangerous
for them. And the government initially decided they'd just try to let that thing happen naturally. The
problem for us with Corona virus is it's too dangerous even for people who are
apparently healthy. You just can't know if you get it. Will you just recover and
be fine and now resistant or will you end up in hospital? And so they're having to manage
the course of this disease, keep us at home, try to delay the transmission
so that the NHS can actually cope with the number of sick people. But in the end, that's what we want to do.
And, of course, the very best way to build resistance and turn us all into purple for Artillery's is
to have a vaccination that is by far the safest way to have herd
immunity in a population. So let's all keep our fingers crossed for all those hardworking people
out there who are trying right now, including some of my colleagues at Oxford University, to develop
a safe and effective vaccine. So just to finish, what can you be looking out for in your garden
this week? We'll have a look around, and I bet you'll be able to find quite a few white versions
of various common plants in my garden. There are white Forget-Me-Not.
In amongst the blue ones, there are white snakes at facilities and amongst the purple.
And there are white bluebells in amongst the blue ones. Gardeners
really like having unusual colours of plants and those loss
of function mutations that knock out the unthaw signs are quite common,
creating white forms of different flowers which gardeners then seise upon and grow.
If you're really lucky, you might find an even more unusual colour mutant. And some people have made a lot
of money out of that by then selling it to the garden industry. So worth keeping your eyes peeled.