Inbreeding | Biomolecules | MCAT | Khan Academy
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Inbreeding | Biomolecules | MCAT | Khan Academy


So today, I want to talk to you
about the effects of inbreeding and how it’s not really
the best for a population. So before we do
that, let’s review the concept of
natural selection. And natural
selection is the idea that a member of
a population that has a special genetic
trait that’s advantageous is more likely to live to an
age where they can reproduce and pass on that special
trait to their offspring. And you should also remember
that a population can get a lot out of
having a big gene pool. And the bigger the gene pool,
the more genetic diversity the population has,
which allows the group to adapt to many different
environmental changes. So what is inbreeding, exactly? Well, inbreeding is when
people in a population will selectively have offspring
with a certain smaller group within that
larger population. And this can be for
a bunch of reasons, like religion or culture,
or maybe just because of preference. And when inbreeding occurs
with non-human populations, it’s almost always due to
geographical barriers, where the greater population
simply isn’t accessible. Now, when people usually
think of inbreeding, words like “incest”
come to mind. But inbreeding really
isn’t limited to members of the same family having
offspring together. Lots of small religious and
cultural groups in the world have some people
with common ancestors and are only distantly related. So you can see that the
effects of inbreeding can exist without close
relatives actually having children together. So why is inbreeding a
problem in the first place? Well, let’s look at an example. So Tay-Sachs disease is an
autosomal recessive disorder. And what that means
is that people with no copies of the genes
are unaffected by the disease. And I’ve drawn these
people in blue. People with just
one copy of the gene are not affected by the disease,
but are carriers for the gene. And I’ve drawn
these people in red. And people with two
copies of the gene are affected by the disease. And I’ve drawn these
guys in purple. So let’s say we have someone
who’s a carrier for Tay-Sachs. So he has just one
copy of the gene. If we’re looking at
the general population, we can see that the odds of the
person choosing a mate that’s also a carrier for the
disease are pretty low. And if he eventually has
some kids, none of them will be affected by the
disease, and only a few will even be carriers. It’s likely that the
copies of the gene will be so spread out
among the population that it would be quite
rare for two carriers to actually end up
mating together. Now if we look at
an inbred population where a bunch more people could
be carriers for the disease, the chances of our guy choosing
a mate that’s also a carrier are a little higher. So more of his children will
be carriers for the disease. But there’s also a chance
that some of his offspring may get two copies of
the gene and actually be affected by the disease. Now, we just talked
about an example with an autosomal
recessive disorder. But maybe you’re
wondering how inbreeding affects autosomal
dominant disorders. Well, let’s look at
Huntington’s disease, which is autosomal dominant. And since this disease
is autosomal dominant, if a person has no
copies of the gene, they’ll be unaffected
by the gene. And I’ve drawn these
people in blue once again. However, if a person has either
one or two copies of the gene, then that person
will be affected by the disease either way. And I’ve drawn both of
these people in red. The key difference
in this case is that no matter who the guy
has children with, even if that guy just has one
copy of the Huntington’s gene, there’s still a
chance that there will be children
affected by the disease. Now, of course, if our guy
has children with someone who was also affected
by the disease, then more of his children
would be affected. But there’s still a
chance either way. Now, one of the other reasons
why we’re less concerned about inbreeding affecting
autosomal dominant diseases is that carriers for
dominant disorders are generally aware that
they’re affected and are well aware of the risks of them
having diseased children. With recessive disorders,
carriers usually don’t have any symptoms at all. And they may not even
know that they’re carriers until they’ve
had a diseased child. And this makes it
much more important for people in inbred populations
to seek genetic counseling so that they are aware
of the risks of them having diseased children. So what did we learn? Well, first we learned that
certain inbred populations can have many more
individuals that may carry a diseased chromosome
than the general population. But we also learned
that this is mostly a concern with autosomal
recessive diseases, since those generally
go more unnoticed than dominant ones do.

14 thoughts on “Inbreeding | Biomolecules | MCAT | Khan Academy

  1. we all know inbreeding is most common in islands. Thats what made you pirates the most ugly people in Europe. Greetings from one of your former colonies. 

  2. You would expect that Evolution would balance this out with all the random mutations in existing specimens.

  3. i can't get past his fake NPR podcast voice. why not just talk normal? who came up with this sound?

    moving on to nikolai's videos.

  4. aa for the autosomal dominant should be unaffected. Pretty big concept to mess up on. Really confused me for a while.

  5. The explanation was amazing, right until he choose Purple, i can't tell apart Purple from Blue, Please next time use something like Yellow or another color more distinguishable from the others. Thanks for the great videos.
    A guy who's mom or dad didn't taught him the colors. Have a great day.

  6. That's why mixed race people have such an average (thus beautiful face) compared to children of homogenous populations who often look "weird" with common traits that are exaggerated!

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