- [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.