All language subtitles for 37031x_MH_Overview_03_Gene_DNA_definitions_v1-en

MICHAEL HEMANN: Let's think broadly.

We're going to start with this issue of, what is a gene?

And this is an issue that people have sort of struggled

with for the past 150 years.

And there are actually multiple definitions of what a gene is.

And over this next number of lectures, four or five

lectures, we're actually going to go

through a number of these possible definitions, right?

And the first one is a gene is just a sequence of DNA.

And that's what we'll talk a little bit about today, just

a stretch of nucleic acids.

The second, which is really an earlier definition and perhaps

now even still the predominant definition,

is a gene is a functional unit.

So, essentially, a gene corresponds to a phenotype.

So we have the gene for ACHOO syndrome

or the gene for cilantro's soap taste.

And that's what we refer to things,

generally, in a population, do you have the gene for this?

And, again, it's one of the early definitions where

we were thinking about phenotypes before we

knew anything about a gene or a DNA sequence.

So a third definition is an independently segregating unit.

And this is really Mendelian genetics,

which we'll talk about in a couple lectures.

So the idea that we actually have the segregation,

generally, of phenotype.

So it's sort of the interplay of definition two and definition

three that we can actually see the segregation

of different phenotypes.

And so, presumably, we have these independently segregating

units.

We can look at second generations

and see things that we don't see in, first generations.

So there's a particulate sort of component of this

that we'll talk about.

And, finally, a gene is a location in the genome.

And this is actually a very important definition.

So all of our mapping studies involves

placing genes or markers next to one another, right?

So we identified genes, essentially, by proximity

to other genes.

We map them to their locations based

on what chromosome they're on, what arm of what

chromosome they're on and, again, their location next

to one another, one another.

And prior to our understanding of the gene

as a sequence of DNA, it was actually unclear

what a gene meant in terms of space at all.

So perhaps it was just sort of a point in the genome.

And so all of these mapping studies

actually preceded any notion of what a gene actually

is in a physical sense.

So, as I mentioned we knew a lot about genes

from a period of time dramatically before we actually

knew the sequence of DNA.

So we understood inheritance patterns with work of Mendel

that we'll talk about.

We understood that DNA was the genetic material about 100

years ago and really foundational studies,

biochemical studies.

But it was really only in 1953 through the work

of Rosalind Franklin, who did the crystal structure of DNA,

and Watson and Crick, which sort of took her work

and elucidated the structure based on her work,

that we understood what DNA was really as a physical entity.

So as you all know, DNA has this double helical structure.

And it's a really beautiful structure.

But the importance of this was not that it

was a beautiful structure.

It was that it actually provided a way

that we can carry information from one

generation to the next.

It provided a strategy for copying information

based on base pairing.

And so, as you all know, we have adenine and thymine base pairs.

We have guanine and cytosine base pairs.

This base pairing actually is a templated process

that directs the transmission of information

from one generation to the next.

And so we'll talk just a little bit

about the physical structure of DNA here or the basic processes

that it regulates.