Selective Breeding – 4.8, 4.9B, 4.14

Hi. My name is Doctor. My Ivory.

I'm Electra in the School of Pharmacy and Farmuit sciences

in card of university.

And in series of talks today, we're gonna talk about genetic modification.

So we'll talk about some of the processes used so things like

selective breeding and some of the more modern techniques like

genetic modification.

And we'll talk about their impacts, so some of the ethical,

and scientific implications of their use,

and we'll talk about some tissue culture as well.

So, selective breeding has been around for many thousands of

years, and it's also called artificial selection.

So if you think about natural selection,

which is covered in a different talk, then that's a way that

nature kind of selects for the most,

the fittest animals, so survival of the fittest,

artificial selection, we pick, as humans,

we pick the characteristics that we want in organism,

and we artificially breed for those.

So it may be aligned with characteristics that help an

organism survive, so it might be things like

being able to survive in more extreme temperatures so they're

more hardy animals.

But quite often it's being more productive.

So if they're animals that we breed for food, then it

might be that we breed something like a sheep to

produce more milk.

And we can also breed sheep that produce more wool,

so that's more useful to us.

It might be that we breed plants.

So if we're looking for strawberries that are

particularly large in sweets, we can use selective breeding

to produce strains of strawberry that are much larger

and sweeter than you'd find in the wild and it can also be

that we breed our pets. So,

dogs there's lots of different varieties of dog and some of

them are bred for the way they look.

So things like pugs are bred to have very short snouts.

But a very gentle temperament.

So over time, we've bred dog varieties.

If they're gonna be kind of house pets that have very

gentle temperaments,

and we also have things like hunting dogs who are good at retrieving,

and finding animals, things like that.

Comparing it to to Mendel's work,

and there's a talk on the work of Gregor Mendel in genetic

outcomes when you breed two different organisms. We

artificially choose for the characteristics that we want so

we're discarding

certain genes. So if, a dog doesn't look the way that we're aiming for.

It might be that we don't use that dog to produce a new

litter of puppies.

And so it kind of removes that set of genes from the gene pool,

in the population.

So over time,

we're able to produce very markedly different traits to

those original wild animals.

And this is just like evolution in that it's not a rapid

process. It's very unlikely if you took a wild strawberry.

And produce lots of strawberry plant plants from it that you'd

end up with one plant that produced the perfect

strawberries chance are you're gonna have some plants with

slightly larger and sweeter fruits and you'll then

interbreed those with other plants with larger sweeter

fruits and then over many generations you get that

incremental change that ends up with the perfect strawberry

that you're looking for.

So we can also use it to produce new breeds of

animals or new varieties of plants that don't exist in the wild,

and it doesn't require us to use any lab equipment So all

you need is the the animal or the plant that you're looking

to selectively breed and the conditions in which they can grow.

So I mentioned some of the characteristics that we might

breed for. So in amongst that, we've got yield.

It might be that you breed for fast growth.

So if you're farming chickens and you can produce a breed of

chicken that grows twice as quickly as normal,

you'll be able to produce twice as many chickens

and as a farmer,

that's great for you and great for the people you're trying to

feed as well. It might be that you breed for flavor, so Some

natural plants are very bitter, but through selective breeding,

we've produced modern varieties that we can grow,

and taste nice. So we can use them for food.

It might be that you breed for disease resistance.

So if you've got individuals that are better able to resist disease,

then you might breed them and you'll have a much harder population.

It might be that you breed them to be suitable for the

environmental conditions that they live in.

Or it might be that you're doing scientific research and

you want animals that you can perform studies with that have

certain characteristics.

And so you breed for animals that have that characteristic,

and then you can have a much more controlled population.

So if you breed for, let's say, aggressive mice and

you're looking to do some behavioral studies,

if all of your mice are aggressive to start with,

that a much easier study to run than if you've got some that

are aggressive and some that aren't.

So it's all about designing a good, well controlled experiment.

There are some implications that come with selective breeding though.

It's not just something that we can do without any impact whatsoever.

So it will alter the genetic variation within a species. So

as I mentioned before,

if you're selecting for one positive trait,

chances are you're gonna select out all of the versions of the

gene for that trait that don't have the characteristics.

So you're selecting out negative characteristics.

So that might be great for you.

But it might be that that gene is associated with other

characteristics of an organism as well.

It might be that having a a shorter snout in a dog has

effects on other systems in the body,

and if you think about pugs,

they tend to have breathing difficulties.

And so natural selection wouldn't have

kind of prioritized that trait.

Because if they're less able to breathe,

then if they have to hunt for food or if they have to escape from a predator,

they're not gonna be able to breathe as well and chances are

they're not gonna be able to escape as well.

So that can have a negative impact that may be unforeseen.

It does also reduce the genetic diversity in a population as

well. So

especially if you've got real inbreeding going on in the population.

So you're just taking a very small number of animals and

using them to produce a wide, a high number of offspring,

and then interbreeding these offspring as well,

you're gonna have lots of recessive traits and we'll talk

more about that in another talk,

that come to the fore.

So what might be very rare genetic conditions normally

become much more common, and lead to unhealthy animals or,

deaths in the population.

Can also be that changes in environmental conditions can

put a population at higher risk. So especially with things

like crops, where,

people have spent generations and generations developing

these selectively bred, varieties

if you've got a new disease that emerges, so, let's say a

bacteria evolves to affect your crop, or there's a new pest, an

invasive species perhaps,

If all of your plants are exactly the same genetically,

because they've been selectively bred,

or have very narrow genetic diversity,

then they're gonna be at risk that that whole population

either succumbs to the disease or is eaten by the pest,

and because they don't have the resistance that you might find

in a few individuals in a more genetically diverse population.

So essentially what we're doing is just stopping survival of

the fittest and kind of tailoring animal populations

to our own needs. And so it is similar in a way to

genetic modification,

and we'll talk later about the controversies that exist with

genetic modification.

But it is something we've been doing as a species for for many

generations just with a little bit less kind of precise

technology than we'd use in genetic modifications where

we're altering the genome. Organisms directly.

So moving on to tissue culture then, and this is a way that we

can develop organisms and if we are looking at producing

clones of plants,

then tissue culture is a way that we can do that.

So if we let's go back to our strawberry analogy. Or example,

that if we had our perfect strawberry plant,

there's only one of them,

and we wanted every offspring of that plant to have those characteristics.

If we bred them through sexual reproduction with another

strawberry plant, using pollen,

then you're gonna have diversity because there's gonna

be a variety of genes.

Some of them might have the the perfect characteristics,

but some of them might have the characteristics of the other

plant that you've used. And so you won't get

a broad population that has the characteristics.

So we might instead want to clone the plant

So what we can do is

use plant tissue culture.

And if you wanna think about it as of a an artificial version

of asexual reproduction,

so producing genetically identical offspring from an

individual And the way that we do that is we start off with

our plant, so let's say our very tasty strawberries,

and we isolate a small piece of the plant it's normally a root

or shoot tip and if you watch the talks on plant structure,

you'll understand that the stem cells in those tissues make

them ideal for use,

in cloning plants.

So you take this tissue,

this plant tissue and you put it on some growth medium,

it might be a liquid broth or it might be agar jelly,

which is a bit more solid. And then you put in some nutrients,

so the stuff that cells need to help them grow and multiply.

And then you also put some growth hormones in there as well.

And it's important with any tissue culture that you

maintain aseptic conditions because you've got a growth

medium with lots of nutrients in it.

And so anything that kind of floats in there. So,

there's lots of bacterial spores in the air.

There'll be fungal spores. If those get into your culture,

then they're gonna grow because you've got really nice

conditions for cells to grow.

And it could affect the growth of your plant.

So aseptic means nice and sterile.

Apart from the thing that you're trying to grow in there.

So when you've got these growth hormones and you've got the

nutrients in there,

the plant tissue that you've put into the culture will

produce roots and shoots of its own.

It'll do so based on the signals delivered by the plant hormones.

And these, when they get to a big enough size,

you've got established roots and shoots,

you can then transport this tissue into soil as you

normally would and grow up these clones and these clones

will then grow into full size adult plants that you can use

to grow all the strawberries that your heart desires.

So it's really useful if you do wanna create those genetically

identical copies of a plant It's much faster than selective

breeding and much less variability in the results.

And the advantage as well that you can also because it's

performed in a lab. You can do it at any time of the year.

You've got very small bits of plant that you're using to kind

of start growing these clones,

and so it's quite space efficient as well rather than

trying to breed full size plants.

So as well as culturing plant tissues using tissue culture,

and we can also use animal tissue culture.

And it tends to be used for slightly different purposes.

So instead of growing entire organisms,

on in tissue culture,

We tend to use animal tissue culture for medical research purposes.

And so instead of growing the range of cells that you'd have

in a normal multicellular animal,

you grow a single type of cell,

and this allows you to do lots of nice experiments where you

can study that single cell type in isolation.

So

the data that you produce is less complex because you don't

have any other cells there. So if you're just looking at,

let's say, cardiac myocytes, which are heart muscle cells,

If you're doing a study of a drug on those cells,

you don't have to worry about all of the other cells that

normally be in the body that might interact with those cells

and change the way they behave.

You can look at the cells in isolation.

There's also less ethical issues as well.

So if you're using whole organisms with all their

different tissues there,

there's gonna be lots of ethical implications.

So animal testing is obviously used widely and it's very

important in drug development, but it should only be used,

when absolutely necessary.

Obviously there's a cost of animal life.

There's a financial cost of doing it,

and there's the ethical issues around it. So if you can form,

studies with animal tissue culture,

that quite often removes the need for animal studies as

well. So kind of benefits across the board. Practically,

the way you do is that you take a sample of the tissue that

you're interested in.

So let's say in this case,

we're interested in cardiac myocytes,

so we take a small sample of the muscle from the heart. We

then separate the cells from one another.

So we want them broken up.

So we've got individual cells and we do that using enzymes.

So once we've split apart our cells,

we then culture them either on or in medium.

So it might be that it's a liquid medium or it might be

that it's a solid medium.

And again, like we did with plants, tissue culture,

it'll have all the nutrients that the cells need to survive

and to grow and multiply,

and any other substances

that out alongside nutrients

that the cells need.

So it might be that you put a hormone in there that causes

the cells to multiply,

so that you have a higher number of cells to work with.

If you're using these kind of signaling molecules or if you

have cells that are naturally proliferative,

which means that they reproduce on their own to produce lots of

copies, then whatever medium you put them in,

let's say you put them in a

a flask, so you've got a liquid with cells in it.

If they're growing and growing,

they're gonna cover the area of your flask,

and then you're gonna get to a point where there's no

available space left for them.

So what you need to do is periodically split the cells.

So you take, say,

you split them into two and you transfer half of the cells into two new flasks,

So they'll have twice as much area because you've only got

half the cells in each flask.

And this ensures that you don't have overcrowding and you don't

have cells dying because there's not enough space or

nutrients available for them.

Can also be possible that you might want to freeze cells.

So if you produce lots of cells,

and you don't necessarily need to use them all immediately,

you can freeze a proportion of those cells and then when it

comes time to do a study,

defrost them and they will wake back up and be ready for use.

I mentioned kind of one of the scenarios where you might want

to use animal tissue testing and particularly cell culture.

If you're testing a new drug and you wanna see the effect of

that drug on cells of a specific organ,

it might be that you do combine or more different cell types to

see the way that they interact.

And if you've got cells in culture,

you can use things like microscopy to observe those

interactions in real time.

Things that you couldn't do if you're using a whole organism,

you can't really put a mouse on a microscope and see what's

happening on a cellular level.

Cell culture is also really useful for studying viruses.

So we'll talk more about viruses in another talk.

But they can't grow outside of sells. So they need cells

to grow and to reproduce in. And so if you want to grow

up a number of virus particles,

you need to use cell culture and to give them the machinery

to be able to reproduce and to make lots of copies of themselves.

Lots of cell lines are developed from cancer.

So I mentioned about having to use chemicals to get some,

cells to reproduce. Cancer cells don't need that signaling,

and we'll talk more about this in the cell division talk that

cancer cells reproduce an unlimited amount.

And so if you have a culture of cancer cells, then you can,

just put them into cell culture. They will merely, reproduce,

and you'll end up with lots of cancer cells that you can use

for your studies.

So obviously lots of work going on at the moment to develop new

treatments for cancer.

And so using cancers, cancer cell lines you can look at

those cells and work out mechanistically so what

mechanisms they use to survive,

and what drugs you can use to disrupt those systems to either

stop cancer growing or to kill cancer cells.

And it's really important because you want a treatment

with cancer that's gonna affect cancer cells,

but not affect related cells in the body that aren't cancer

because obviously you need all of those cells to survive.

And then last but not least, you could also,

this is quite an emerging field.

So kind of watch this space that there's work ongoing at

the moment that if you could create an artificial scaffold,

so kind of a structure for cells to grow on.

That if you populate that scaffold with all of the

different cells in a organ or a tissue, then you might be able

to transplant that tissue into a patient.

And there's hope that one day it might be possible to grow

organs and so you wouldn't need to use organ donation

potentially you could grow up tissues from a person's own cells as well.

So you wouldn't have the issues around transplant rejection.

So it would be a really lovely technology if it was possible,

but because of the complexities of growing all of these

different cells and getting them to attached to a

scaffolding and interact like they would in an organ,

not yet possible.