- [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.
