Meiosis II is composed of the same phases. Very familiar
operations. Prophase II, metaphase II, anaphase II,
telophase II and then certainly cytokinesis.
So in prophase II we have two daughter cells
resulting from prophase I that now have different
genetic content than the parent cell because we have
separated homologous chromosomes. Right? So we have
reduced chromosome number. Think about this for a moment.
We started with 46 chromosomes. We lined them up in
pairs down the metaphase plate in metaphase I,
and we separated each of those into two new nuclei.
So we have 23 in here, and 23 in here.
Now, we are going to separate sister chromatids.
So, in metaphase we will see that, in metaphase II,
we're going to see that the chromosomes align on the
metaphase plate. As they align on the metaphase plate,
you can see there is some genetic recombination that has
occurred. And we see them lining up again single file.
So, don't you think that metaphase II of meiosis looks
fairly similar to metaphase of mitosis right?
Think for a moment. What is the difference here?
How is this different than mitosis?
We have a reduced chromosome number. So if we were
looking at a human cell here, rather than 46
sister chromatids sets lined up down the center, we've
already reduced it by half. We had 23 here. 23 here.
So we have half the number of chromosomes lined up down
the center of the cell. By the way, each sister chromatid
is one molecule of DNA. So one long molecule of DNA
has been copied into another long molecule of DNA
and these are all tightly supercoiled. So in the
sister chromatids, we have two molecules of DNA,
two molecules of DNA. And those two molecules are about
to separate in anaphase. This stuff should be quite
familiar by now, right? So as we move forward,
in anaphase we see that the sister chromatids
are pulled apart. Again, language is critical here.
Just as in anaphase of mitosis, anaphase of meiosis II
we're separating sister chromatids. Think back.
What was the difference during metaphase and anaphase I?
What were we pulling apart during anaphase I? We had
homologous chromosomes aligned, popped them apart.
We were pulling apart replicated homologous chromosomes.
So the language again, very important to understanding
and being able to answer exam questions on meiosis and
mitosis. So telophase, we all know what happens.
The nuclear envelope reforms. We now have
four distinct cells or four distinct nuclei,
and then cytokinesis will follow. We'll have four
distinct cells. Now the cool thing is
here they are genetically recombined and genetically
shuffled. So unlike mitosis, the resulting cells
from meiosis are genetically distinct from either of
the parent cells. Whether it's sperm being produced
or eggs being produced, those are genetically distinct
from the parent cells that produced them.