Asexual and sexual reproduction | High school biology | Khan Academy
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Asexual and sexual reproduction | High school biology | Khan Academy


– [Instructor] Let’s talk a
little bit about reproduction. Now, on earth, and who knows
if we go to other planets we might find new ways that
organisms can reproduce. But on earth, there’s two primary ways that organisms reproduce. The first is, is that,
let’s say this is some type of unicellular organism,
it essentially just makes a copy of itself. So that’s it there, and
then that’s its copy. And in this situation they have
identical genetic material. So let’s say this is the
genetic material of the first one, and this is the
first one to begin with, and now you have the second one. Now this type of reproduction,
where one organism by itself can turn into two
organisms, this is known as asexual, asexual reproduction. Or another way to interpret
asexual is it is not sexual. So the next question is,
what is sexual reproduction? This is where two
organisms, or at least cells from two organisms, need
to get together in order to produce a third organism. Here’s a cell from one of
the organisms, let’s say that cell is from the mother,
it could be an egg cell. Here’s a cell from the
other organism, let’s call that organism the father,
this would be a sperm cell. And when the egg and the sperm
get together, when they fuse together, they have genetic
information from both parents. And that new cell can
become the offspring. And if sexual reproduction
sounds familiar, it’s because that’s how you came to be. Now, to make this a little
bit more tangible, let’s look at some cases of asexual reproduction and sexual reproduction. So right over there we
see a diagram of a type of asexual reproduction
known as binary fission. In general, if you hear the
word fission we’re talking about splitting something,
if people are talking about nuclear fission they’re
talking about splitting of the atom, but binary
fission we’re talking about one organism splitting into two organisms. And you can see that you
have its genetic material, the genetic material it
replicates, and then the organism splits into two identical
organisms, or at least identical from a genetic point of view. Now binary fission applies to prokaryotes that we talk about in other videos. These are organisms that don’t
have organelles, that don’t have a nuclear membrane,
they don’t tend to have multiple chromosomes. When we talk about eukaryotes
things that do have nuclear membranes, things that
have multiple chromosomes, things that have membrane-bound
organelles, you have a similar type of reproduction. This right over here, and
we’ll study it in depth in biology, this is mitosis. And mitosis you can view it as
the analog of binary fission but we’re now dealing
with eukaryotic cells. Eukaryotic cells are more
complex, so this process is more complex. But at a high level, they’re
both asexual reproduction. In both cases, one cell or
one organism in some cases, has turned into two organisms
that have the same genetic information. And it’s worth calling out
when you take one organism and you produce another
organism with the same genetic information, it has
a word associated with it, and that is a clone. And you might be familiar
with the term clone from science fiction movies,
and they usually use it in a somewhat related context. In Star Wars when they
talk about the clone wars all of those clones they all have the same genetic information as
the original bounty hunter from which they were derived. Now mitosis might also
seem familiar to you because this is how most of your cells in your body divide. And this is how you grow,
this is how you went from being a unicellular organism
to being a multicellular organism. Now you might be a little
bit confused at this point. I just told you that most of your cells have experienced or are
experiencing mitosis, but you’re also the outcome of sexual reproduction. Well what we’ll see in a
second is, as soon as sexual reproduction occurs, then
this newly formed cell right over here, through
mitosis forms the multicellular organisms, the types that
are you and me, but we also as we grow and develop, we
also produce what are known as gametes, that each have half
of our genetic information. For human beings, this
would be the egg produced by a female, and this
would be the sperm produced by a male, and when they
get together, the sperm fertilizes the egg, well
then, they can produce a viable cell that can
turn into an offspring. Now along the lines of binary
fission, you have another type of asexual reproduction
in which case a mother cell produces buds off
a smaller daughter cell. So like binary fission, it has
to replicate all of its DNA and then that DNA gets
inserted into the daughter cell but the end product you have a bigger cell and a smaller cell. And we would say that the
smaller cell has budded off of this larger one. And so this we call budding. Another form of asexual reproduction. When we think about
multicellular organisms there are some typical types of
asexual reproduction. For example, starfish are
famous for their ability to form a new organism
from a piece of an original organism, so let’s say
you were to cut that part off of the starfish for
many species of starfish that could then grow into a new starfish. The original starfish
would grow that back. And so this type of reproduction
is known as fragmentation. It’s pretty easy to,
fragmentation, it’s pretty easy to remember, you take a
fragment of it and it grows into another organism and
that’s how it reproduces. Now another fascinating
type of reproduction is known as parthenogenesis,
that’s a fancy word, partheno, parthenogenesis. And what happens here is
is you have an organism, and this is a baby komodo
dragon right over here, that can develop from an unfertilized egg. Remember in sexual
reproduction we talk about how a sperm from a father organism needs to fertilize an egg
from a mother organism and then once they fuse together
then that fertilized egg can go through mitosis to
produce a multicellular organism. But in parthenogenesis,
you have an egg on its own that can, that does not need
to be fertilized, that can turn into a multicellular organism,
like a baby komodo dragon. Now you might ask, well how can this be? Well, sometimes these mother,
these eggs, don’t have half the genetic material
like we’re used to with the eggs from sexual reproduction. For parthenogenesis, many times
this egg has a complete set of genetic information
and then it can just go and start doing mitosis
and turn to an organism or there’s even situations
where the egg does have half the genetic information,
we’ll talk about this in future videos, this
would be a haploid cell, it has half the genetic
information of its parent, but the haploid cell in
certain cases can develop into a full organism. And there are organisms
like komodo dragons that can reproduce both with
parthenogenesis which would be asexual, and in certain
cases with sexual reproduction. So I’ll leave you there, two
big categories, I’ll draw a dividing line here so
we don’t get confused. All the stuff that I drew
on the left, to the left of this yellow line, these are forms of asexual reproduction. Where for the most part,
one organism can make a copy of itself that has the
same genetic information. On the right we have sexual
reproduction where in order to produce a new organism,
an egg cell and a sperm cell need to get together. The sperm cell needs to
fertilize the egg cell and each of them would
have a sample of half the genetic information from their parents. Now, I’ll leave you with a
final question, we should always be asking this in
biology, is why do we think sexual reproduction emerged? It actually emerged much later
in our evolutionary history than asexual reproduction. Well one argument for it
is is it produces much more variation in its offspring. And if you have more
variation in your offspring, and if you have more
variation in a population, you have a higher likelihood
that certain variations will be better suited for the environment that you are in. I’ll let you think about
that a little bit more.

13 thoughts on “Asexual and sexual reproduction | High school biology | Khan Academy

  1. The intonation at the beginning of your sentences is different from before… You tend to drag them out with a hoarse voice in high pitch which sounds creepy. Well any change is creepy to humans. Great work.

  2. Hey khan organization im from kurdistan iraq , and i really get benefit from your organization , god bless all of you

  3. And then certain scientists want to make modular cells. Maybe it's possible, but we're not there yet. Although they made lipid spheres that can divide and contain working proteins. They can even get imagination working to get vessels with molecules and viruses into the cell.

  4. you're saving the life of this freshly-graduated high schooler from possibly failing college entrance exams, thank you

  5. Wrong the Kimono dragon produced sperm from Failed eggs and young were still diploid the eggs that did hatch well didn't hatch they never got passed embryonic stage

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