So, now that we have established mitosis from
meiosis, I'd like you to recall which division
is the reduction division. Where does the cell
become haploid? The key here to remember, I can't
emphasize it enough, is haploid happens at
meiosis I, right. So keep that in mind.
Let's compare mitosis to meiosis very quickly. We
know that meiosis has two phases and mitosis
has only one phase. We know that meiosis looks
very much like mitosis in meiosis II
because we're separating sister chromatids. Meiosis I
doesn't look anything like mitosis because
we're separating homologous chromosomes. I mean it
looks something like it because we're separating,
I mean we have all the same spindle fibers and all
the apparatus is the same, but meiosis I
is very different because of the homologous chromosome
pairing. Now, also we end up with identical cells
at the end of mitosis. And at the end of meiosis we
end up with four genetically distinct gametes
or sperm and eggs. So we can go all the way through
meiosis I, and it's not until meiosis II that things
start looking the same. Many questions you will run into
here concern the chromosome number. How many of what
are in prophase. How many of what are aligning on the
metaphase plate. So, diagram these processes,
compare and contrast, think about the number of
chromosomes and how many molecules of DNA end up in
meiosis I and how many molecules of DNA end up
in each cell at the end of meiosis II.
And compare and contrast those to what's happening
during mitosis. Who pairs on the metaphase plate
is the critical question. If you understand that, you're
really set up for success. So in this lecture,
we recalled the language of chromosomes. And I hope you
can see how important it is to really have a great
understanding of those, of that language. And in
addition to that, we started to distinguish
features of meiosis. One of those was the genetic
recombination. We have pairing of homologs
and synapses. So we have crossing over, exchange of
genetic information. We also have
arrangement of chromosomes on the metaphase plate.
It's random. So, we mix things up during meiosis.
We also should be able to summarize how genetic
variation occurs during meiosis.
So those were the mechanisms to acquire that.
And also relate meiosis to gamete formation.
So how does meiosis reflect in the female reproductive
system versus the male reproductive system.
And finally, really good idea to be able to line these
three events up and compare and distinguish between
mitosis versus meiosis I and then meiosis II. So
hopefully this lecture clarified for you
some of the details of what's going on during meiosis
and why meiosis is important for sexual reproduction.
Thanks so much. I look forward to
seing you in a future lecture.