All language subtitles for 37031x_PR_Mendelian_Genetics_03_Setting_Up_Experime-en

PETER REDDIEN: So let's do some experiments now

to try to distinguish between our hypotheses.

So any suggestions?

Yeah.

STUDENT: You can see if the fly's offspring are paralyzed.

PETER REDDIEN: See if the fly's offspring

exhibit the same trait.

So we'll set up a cross with this fly.

So we'll take a paralyzed fly--

our paralyzed fly-- now, we only have one of it.

We found this one fly.

And we will then cross it, so this

will be my notation for a cross in this course,

meaning some mating that we are setting up as desired

between two individuals.

So we'll take some non-paralyzed fly.

So this non-paralyzed fly we're going to call wildtype, or wt

in short.

That's the phenotype of this other fly.

So we've got a paralyzed phenotype

and a non-paralyzed phenotype, or a wild-type phenotype.

And we set up a cross.

So we look at the progeny.

The offspring in an experimental cross

between two different individuals,

the first generation is called the F1 generation,

or the first filial generation, is on the board.

The first generation produced by interbreeding of two lines.

So we can look at the phenotype here and what we see

is that they're all not paralyzed.

What is this new information do for us with our hypotheses?

If anything?

What do you think?

- Overall, so the suggestion was to do another cross

that this is not necessarily excluding

that genetic hypotheses.

Often what you are doing is in science--

getting some observation where you see something happening,

you try to come up with reasonable explanations that

are possible with the data you have,

and then you're seeking to exclude certain hypotheses

to find data that would be inconsistent with predictions

of those hypotheses.

So that's often what we're doing as we're

walking through some genetic experiments as well.

So at this point I don't think we

can exclude any of our hypotheses that we had before.

So-- but the suggestion was good to do another cross.

So we'll take this F1 and we will set up

a cross between two F1s, siblings,

and we'll look at the next generation.

This will be the F2 generation.

And when we look at this F2 generation,

we will see that the paralyzed phenotype has re-emerged.

Some are paralyzed.

So this might exclude some of our hypotheses--

accident, or old age, something like that.

It seems to exclude those.

Maybe they still could be some kind

of virus that's popping around or something like that,

so we'll continue to do some experiments to try to resolve

all the possibilities.

But this is starting to support that there's

something heritable here, wasn't just some accidental thing that

happened.

Something has led to this being propagated

through these individuals.

Most will be wild type in phenotype.

All right, now we're seeing a-- this discrete nature

of this phenotype through these process where it's either not

paralyzed or paralyzed and it's seemingly

can not be visualized in some individuals

and then reappear in some of their offspring.

So this-- these are good traits to be working

with for some straightforward genetics when

you can have much more complex inheritance patterns that

will get into, where it's not quite as clear.

So now we're going to take two F2 individuals,

so F2 paralyzed cross an F2 paralyzed individual

and we can look at their progeny.

Any predictions?

Yeah.

STUDENT: 100% paralyzed.

PETER REDDIEN: 100% paralyzed and that's what happens.

Now, we could do some control crosses where we take wild-type

flies and cross wildtypes to one another--

not from the F2, these are from the wild.

So these are from the wild, let's say.

So we cross these to one another and we see 100% wildtype.

We could keep doing these crosses

and they will continuously give us the same outcome.

So from crosses like this what we can see

is that the trait we're looking at is so-called true-breeding.

A strain that when crossed always

produces the same phenotype.

So we have generated a set of animals

that are true-breeding now, that all have this phenotype,

and those individuals can be called a strain.

And we have generated two strains, a paralyzed strain

and a wild-type strain.

And working with true breeding organisms

is really important in genetics because you

can have traits that are--

what you'll-- will come to like these F1s in a heterozygous

state where you could see the phenotype emerge in different

generations.

So I'll come to that.

But what we're working with now are true-breeding strains.