Biotechnology Lecture Part 5


Another interesting use of biotechnology is
DNA fingerprinting, and this is when you use DNA to identify specific individuals. So if
you’re a murder mystery TV show fan like me, you know that we use DNA all the time to try
and identify individuals at a crime scene, or if you watch bad TV in the mid-afternoon,
you know that we use DNA fingerprinting to figure out who the dad is… so law-enforcement
and paternity are one of the main ways that we use DNA fingerprinting, although there
are other ways that we do use it. So here’s the steps that you go through in order to
do DNA fingerprinting. First you isolate a sample of DNA. Then, you are going to subject
that DNA to some restriction enzymes, and these are just specialized molecular scissors
that cut the DNA in regular spaces. So it may look for CCAATTG and it will cut every
time it reaches that particular segment. Then, you subject those pieces of DNA to a process
called PCR – polymerase chain reaction – and what it’s going to do is rapidly make millions
of copies of those pieces of DNA. So you’re going to run your DNA through these three
steps. Denature – the DNA comes apart, that’s by putting it at a very high temperature,
but only for a minute, because we don’t want the DNA to completely fall apart. Then you
cool it down, you add some RNA polymerase and a primer, and it starts to build more
DNA … annealing … extension … and then you stop again, denature … anneal … extension,
denature … anneal … extension. You only give it enough time to copy small segments,
but if you do this for 30 cycles, you’re going to end up with 2 billion copies of those
DNA fragments. And now you have enough pieces of DNA to actually physically see differences
in the sizes of those little pieces. Then we’re going to take those little pieces
and run them through a gel electrophoresis. The DNA is injected into a gel, and this is
like a clear piece of Jell-O, made of agar. We’re going to run an electric current through
the gel. DNA is a negatively charged molecule, so it’s going to move towards the positive
charge. But here’s the key, large pieces of DNA move more slowly than smaller pieces.
And so all those different fragments are going to get separated out by their size. And what
this is going do is create a distinctive banding pattern. Here’s an example of the results
of a gel electrophoresis. So we’ve injected DNA down at the bottom here. We’ve run electricity
through. And all these different bands represent different fragments of DNA. The ones that
are up here are going to be the shortest, and the ones down here are going to be the
largest. You then can compare unknown samples of DNA to known samples of DNA fragments.
It turns out that, because we each have a unique DNA code, the size and number of different
fragments that are produced by those different restriction enzymes are going to be unique
to each individual. Typically, with humans, we look at about 12 or 13 sections of the
DNA, and those will be unique for each person. So here’s an example. Here is the DNA that
we collected from a crime scene, and here’s the DNA from three suspects. We have all these
banding patterns, and now we can just match up the bands. So there’s a band here, this
individual doesn’t have it, this one does, this one does. So, we can let Suspect 1 go.
We’re going to keep looking. Notice, there is a thick thin thick, thick thin thick. This
one doesn’t quite have that, so we can release Suspect 3 and we’re going to arrest Suspect
2 based on the DNA evidence. This kind of DNA fingerprinting is about 99% accurate.
I think many people think DNA fingerprinting means we’re actually matching the individual
genome code of an individual to a sample, so notice here, we are NOT matching A, T,
C’s and G’s. If you were able to do that, then this would be 99.99999% accurate. Instead,
we’re just chopping your DNA up into pieces and matching it to a sample of DNA that’s
been chopped up in the pieces. However, even 99% is very, very high accuracy. The last
topic in biotechnology is genetic testing. And you can watch this video that talks about
some of the kinds of testing and some of the implications of it. There are different kinds
of genetic tests out there. So the company 23andMe is a private company that you can
go to their website and they will give you the option to get a kit. It’s probably about
$99 for their basic kit. You can a spit in it. It’s going to go to their lab, and they’re
going to give you information. That information is going to look at your genome and look at
probabilities of having certain diseases. Now this is classic correlation science, where
they’re going to say “oh you have this particular gene which gives you an 18% increase in the
chance of having heart disease” for example. Does that mean you’re going to get heart disease?
No. It’s just looking at the broader population of people and who tends to get heart disease
more than others. It doesn’t say anything about what you’re eating or if you run every
day, and so remember that genetic analyses are just one one piece of understanding your
health, and it’s best if you’re getting that kind of genetic information to work through
it with a genetic counselor so that your understanding the real implications of whatever information
you gte. And it’s interesting for you to think about right now – are you someone who
would rather know an increased risk of a particular disease? Or is that not something that you
would want to know? So everyone’s different about how they feel about genetic testing
and what they want to know. There are other programs like this personal genome project.
And this is a public effort that Harvard is trying to do to gather millions and millions
of personal genomes and start to create a database from which scientists and doctors,
so they can analyze specific diseases, specific genotypes, and try and make connections that
maybe aren’t obvious about who may be susceptible to certain genes [diseases]. It’s sort of
a neat project and it will certainly contribute to the public good, but there are concerns
about privacy and what kind of information will be found and who will be shared with.
So there’s really an ongoing debate about genetic information and if that should be
shared or not. About six or seven years ago, Congress passed a law that said it is illegal
to discriminate against someone based on their genetic information. There was a lot of concern
that if you got tested, for example, for the breast cancer gene, that may be would be able
to get insurance because insurance companies would look at you as a future risk. That’s
been made illegal, but it’s a brand-new world of having all this information and so no one
is quite sure how this is going to play out. Finally, there’s another level of genetic
testing, which is not testing so much you as an individual and potential diseases, but
looking at what part of the planet your ancestors came from. You can look at mitochondrial DNA,
you can look at other specific parts of the DNA that are good indicators of your ethnicity.
They can really pin down the particular parts of the planet that you’ve come from. Again,
this is something where you spit in a test tube and send it off, and they will send back
this information, giving you sort of approximately what part of the world your ancestors came
from. There is a professor at Harvard, Henry Louis Gates, who is the head of African-American
studies, and he actually is a TV show on PBS that goes through this kind of activity. He
got himself tested and he certainly identifies as an African-American man, but when he got
tested found out that he was actually 55% to European, and that he was more white than
he was African-American. But he was also able to identify where in Africa that side of his
ancestry came from. And it sparks some really interesting conversations about race and genetics.
I haven’t done this yet, but I’m very curious about it as I am German Irish and my husband
is Chinese Filipino, and so my kids are going to have dots all over the world map, and I
think it would be kind of fun to see how that would come out. So genetic testing encompasses
very serious disease related conversations and also about race and ethnicity and ancestry
and how we fit into the global human population.