MEIOSIS
Mrs. Kolobaric
Review

What is the purpose of mitosis?

_____________
_____________

Cells Themselves

Every cell has its own life span, all cells
eventually die, so all of them need to replicate
(go through mitosis)
Blood replaces all its cells in about 3 months
 Lungs will replace themselves in 5 years
 Neurons, will never

Mitosis As a Review


Mitosis looks at _______ and _______ of a
single organism
Also explains ___________ of single celled
organisms
An Issue?

What is the problem with having identical cells
as organisms?

Do you see a problem with having identical
organisms in the populations?
The Reality of It

Imagine a million Niki Minaj’s

I like her, she sings and raps well, but is there a
problem,
Is she perfect?
Susceptible to anything?


The Problem




__________________________________
__________________________________
Do we actually find populations that are
completely identical to each other?
________
What is the benefit of not being
Identical?

For ___________, reproduction went from
asexual (mitosis), to sexual (which has a great
deal of diversity)

__________ of the individual does not matter,
but survival of the __________ does
Steps of Mitosis

What are the four steps? What happens in each?

Prophase


Spindle Fibers Appear and Centrioles begin to move to the
different poles
Metaphase
Steps of Mitosis Continued…

Anaphase

Telophase



Nuclear envelope reforms
Cells begin to separate and become 2 different identical cells
Cytokinesis

The 2 _________________ move apart and the cycle begins
again
Cell History


Historically, mitosis evolved before meiosis
So how are you created?

Well you need a ______ and a _______
But….


How can a male with 46 chromosomes, and a
female with 46 chromosomes produce a child
with 46 chromosomes?
Half must come from the mother, and the other
half must come from the father to produce the
baby
The baby will then grow using
___________

Lets Get Started

Who can tell me what the purpose of meiosis is?

The production of ________ in male and _____ in
female, sex cells are called ___________

Lets look at the process of creating the sex cells
happening in both males and females
A Comparison

What happens to the genetic info before mitosis
begins?
It is replicated, two identical chromatids on the
chromosomes
 Well the same thing happens in meiosis

A Comparison

The process of meiosis is a modified process of
mitosis
The First Step

We have duplicated genetic info going into the
first stage of gamete production

What did we call the first stage of mitosis?


______________
What do you think we are going to call the first step
in meiosis

____________________
The First Step…

What happens in prophase of mitosis
The genetic info condenses into visible
chromosomes
 The nuclear envelope disappears
 The Centrioles move apart and start to form spindle
fibres


It happens in meiosis as well
Starts to Disappear
The Second Step

What happens in mitosis during metaphase

Chromosomes line up in the equator of the cell and each
chromosome connects to the spindle fibres

Here is where meiosis starts to change

If we are talking about a human, how many
spindle fibres do we have in mitosis

46, one for each duplicated chromosome
The Second Step

In meiosis, what are we trying to make?


sex cells, but when fertilization takes place, the genetic
material is donated half from mom, and half from dad, so
we are trying to make cells with half the genetic material
So how many spindle fibres form in a meiotic
cell

______
Lets back track a Bit

Because the spindle is forming with 23 fibres
only, and in a human cell there are 46
chromosomes, the 46 need to pair up the
chromosomes

They do this with their "look alike partner“

What do you think i mean by the words “look
alike” partner?
Why You Look Like That

Every sexually reproducing organism gets
_____of its genetic information from one
parent, and _____ from the other
So which parent gives you the information for hair color?
 Eye colour?
 Height?


In actuality, you get this from both parents
equally
Why You Look Like That

If that comes from both parents, we need some
genetic information from dad, and one from
mom,

Does it have to be the same information?
Why You Look Like That

Example, what if mom’s genes says blue, and dad’s
genes said brown eyes?

The information can be different, but its still
information about eye colour.

So the “look alike” partners have information
about the _______ _______, but do not
necessarily have the same identical information,
they talk about the same words
The Look Alikes

Look alike partners actually have a proper name
______________ _________________

What does that mean?
What does that Mean?

What does “homo” mean in Greek?


What does “logos” mean in Greek?


It means the ________
It means ________
Homologous = the same words (or information)
Homologous Chromosomes

Homologous chromosomes contain __________
information

We can think of the genetic material as ____ pairs of
chromosomes

Each pair containing the _________ information.

___ is therefore called the _______ number

___ is called the _________ number

This will be important later on in our discussions
Back To Prophase

The “look alike” partners find each other, or the
__________ chromosomes pair and they form
what is called a ______

The process of coming together is called _______,
so when the process of synapsis takes place, it
forms tetrads
Time for a Bio Break…for Math



Lets pause for a second we need to do some
math
lets take a look at an organisms that has one pair
of chromosomes
How many ways can u arrange the 2
chromosomes when they pair up, lets call one
mom and one dad?

Two ways first one can be mom, and then dad, the second
can be dad and then mom
Time for a Bio Break…for Math

Now, lets double the
mom dad
number of chromosomes mom dad
to two pairs

How many ways can you
arrange 2 pairs?
dad mom
dad mom
mom dad
dad mom
dad mom
mom dad
Time for a Bio Break…for Math

What about 3 sets of chromosomes


8 different ways
What is the relationship?

# of combinations = 2n

(n=number of chromosome pairs)
Time for a Bio Break…for Math




How many different combinations are there for
23 pairs?
223
223 = 8,388,608
Well hold on a second, its not a big number.
How many people do we have on the planet?
The Trick

6.5 billion, and I will bet, that no two individuals
are identical except for identical twins, triplets etc,
and there are not that many of them

So variation in the genetic information can not
only be due to the way the chromosomes line up,
there must be a way to mix up the genetic
information further
The Trick



We have to look closer at the tetrad
As the chromosomes of the tetrad come
together in synapsis, is there a possibility that the
2 chromatids that are on the inside may lie
across each other?
YES! That is a possibility
The Trick

Well what if identical segments
from dad and moms
chromosomes were exchanged?

Now you have ________
diversity, this event is called a
____________

It is a physical exchange of
identical pieces
Where it happens

Does it have to happen at the same place?
Epiphany


No wonder we have so many different people
on the planet with different genetic make ups.
We can have hundreds of thousands of cross
over spots which gives us a lot more variation
Metaphase


Lets move on to metaphase,
How many spindle fibres
did we say will form?


23, one for each pair of pair
homologous chromosomes,
Unlike metaphase of
mitosis, the chromosomes
line up as _________ pairs,
not in single file
Anaphase

What happens in anaphase of
mitosis?



the individual chromatids are
pulled apart by the shortening of
the spindle fibres
Think about a rope tug of war
between the 2 Centrioles
Homologous pairs lined up in
meiosis are pulled apart to
opposite ends of the cell
Daughter Cells

How many chromosomes does each daughter
cell have?

_______________________________

Remember the diversity, tons of combinations,
but what we have done is taken 46
chromosomes and created 2 cells with 23
duplicated chromosomes,
The major Step

Since 46 chromosomes became
23 duplicated chromosomes,
this particular process is going
to be called the _________
________ after telophase is
completed

Telophase is the same as in
mitosis
Are We Done?



We have taken the diploid number ____, and
reduced it to the haploid number___
Do you see any issues with these 2 product
cells?
Each of the chromosomes is still _________,
and contains _______the genetic information,
therefore we must separate the copies.
Another Difference

Meiosis has to go through the process again to
_________ the __________ in each
chromosome.

All we do is repeat prophase, metaphase,
anaphase and telophase the same as mitosis,
except with half the number of chromosomes
The Second Phase
The Second Phase
How we distinguish
MEIOSIS 1
MEIOSIS 2
Prophase 1
Prophase 2
Metaphase 1
Metaphase 2
Anaphase 1
Anaphase 2
Telophase 1
Telophase 2
The Final Tally

Mitosis produces _____ _________ daughter
cells (_________),

Meiosis 1 produces ___ daughter cells with __
_____________ chromosomes

Meiosis 2 _________ the duplicated
chromosomes to a total of ___daughter cells
with a _________ # of chromosomes
But aren't there 2 Kinds?

All organisms produce 2 types of sex cells, male
produces ______ and female, ______.

There are differences in the two processes that
produces these 2 types of gametes, lets look at
them
Spermatogenesis



Proceed through meiosis stage 1 and 2 as
described and at the end,
we end up with 4 haploid cells that are all the
same _____ that contain _____ the number of
chromosomes
Due to cross over they are ____ different,
Spermatogenesis

These cells will then continue to
mature inside the _______
growing a _____ for propulsion,
 a mid piece containing ________
to provide the energy for
movement,
 Package of ________ at the tip
called the _________ which allows
the sperm to penetrate the outer
layers of the egg and form a
tunnel, for fertilization

Oogenesis

Oogenesis is different in the sense that an ____
has to go through a large number of divisions
before it _______ in the uterus and receives
nutrients from the mother

The egg must be ______ and contain a large
quantity of _________.
Oogenesis

The first difference occurs in __________, there
is an _______ split of the cytoplasm where one
of the 2 cells gets the majority (_____) and the
other cell gets _____

even though the small cell has correct genetic
information, it does not have enough _______
to become an egg

It is called a _______ ________
Oogenesis


These two cells go through meiosis 2
The polar body splits into 2 small polar bodies

The large cell splits unevenly to produce the egg
and one polar body

The egg matures just like the sperm did, but in
the ovary and released during ovulation