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Chapter 8: Cell Division

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Yat-Long Poon

on 27 September 2018

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Transcript of Chapter 8: Cell Division


reproduction
at the cellular level
produces
two cells
from
one original cell
requires the
replication of chromosomes
(DNA)
each new cell gets a new copy of DNA
Cell division has many uses
reproduction for unicellular organisms
growth of multicellular organisms from a fertilized egg into an adult
repair and replacement of cells
production of gametes
Metaphase
Telophase
Mitosis
Cell Division
Prokaryotes reproduce
by binary fission
Cell Cycle
Interphase
Prophase
Prometaphase
Majority of a cell's life
Period between cell divisions
Cell is doing its job
Cell is growing
Cell is preparing for cell division
Two
centrosomes form
Chromosomes (DNA) replicated
in nucleus
Mitotic spindle
begins to grow out from the centrosomes.
The 2 copies of chromosomes organize so they can be separated
Nucleus breaks apart to release chromosomes
Mitotic spindle connect to the chromosomes
Mitotic spindle is fully formed
Chromosomes aligned along cell equator
Anaphase
Sister chromatids pulled apart
Mitotic spindle begins to pull the cell apart
Mitotic spindle disappears
Nuclei re-form around chromosomes to create two new nuclei
Chromosomes return to their original shapes
Cytokinesis
Cytoplasm is divided into separate cells

Usually occurs simultaneously with telophase.
Interphase has
3 phases
G1
(Gap 1): Cell is being a cell

S phase
(Synthesis): Cell replicates its DNA.
Centrosomes form
.

G2
(Gap 2): Cell goes back to doing its thang and preps for cell division
Cell division after sperm and egg unite
Cell Division
Chapter 8: Cell Division
Sexual organisms have two types of cells
Somatic cells
Cells that make up your body's tissues

Gametes
Cells that are involved in sexual reproduction
Unlike somatic cells, gametes are haploid
Haploid
: having only
1 set of chromosomes

Do not have chromosome pairs.
Meiosis:
the making of gametes
Meiosis is a type of cell division that
produces gametes
.
Both are
proceeded by interphase
and
replication of chromosomes
.

Mitosis
makes
2 identical cells
.
Meiosis
makes
4 potentially different cells
.

Mitosis
is only
one cell division event
.
Meiosis
is
two cell division events
.
Interphase
Basically the
same in both
meiosis
and
mitosis
.
Germ cell grows
Organelles replicated.
Chromosomes replicated
Somatic cells are diploid
Diploid
: having
2 sets of chromosomes

Every chromosome
is a pair
you have 48 chromosomes total
you have
two Chromosome 1's
,
two Chromosome 2's
, etc.

Human cells have
23 chromosome pairs
.

Chromosomes of a
matched pair
are called
homologous chromosomes
.
Allosomes
(1 chromosome pair)
determine
sex
X
and
Y
chromosomes in humans
differ
in size and genetic composition

Autosomes
(the other 22 pairs)
all other chromosomes
do not determine sex
each chromosome in a pair
same size and has same genes
but can have
different versions
of the same genes called
alleles
The
first cell division
is called
meiosis I
.
It produces
2 diploid cells
.
The
second cell division
is called
meiosis II
.
It produces
4 haploid gametes
.
Meiosis I
Prophase I
Meiosis I
Metaphase I
Meiosis I
Anaphase I
Meiosis I
Telophase I
Meiosis II
introduce genetic variation
into the gametes and into babies

one reason why children don't look exactly like their parents or their siblings

genetic variation is
important for evolution
to happen
Second cell division, but
without the replication of chromosomes.

Each new cell
only gets 1 set of chromosomes
.
Spindle form from centrosomes
Nucleus breaks apart
Homologous chromosomes pair to form
tetrads
Tetrads align at the cell equator
Homologous pairs separate and move toward opposite poles of the cell.
Unlike mitosis, homologous chromosomes remain attached.
Duplicated chromosomes have reached the poles.
Cytokinesis happens
But there's a twist!
Homologous chromosomes come together in pairs during
synapsis
.

In synapsis, homologous chromosomes sometimes
exchange segments of DNA
in a process called
crossing over.
Why do chromosomes come in pairs?
But there's another twist!
When the chromosomes line up at the equator, which new cell they will end up in is mostly random.

This is called
independent assortment
.
This means you can't be sure which new cell will have which parental chromosomes at the end of meiosis.
This produces combinations of genes that did not exist before.
Diploid cells
Meiosis produces
haploid cells
that may be
genetically different

Meiosis only occurs with special cells called
germ cells

Germ cells are
only found in your gonads
(e.g. ovaries and testes)

Other cells in your body do not perform meiosis
So inside your gonads...
Meiosis
Mitosis
Cell division that
is done by
somatic cells
produces
2 identical cells
from 1 original cell
makes somatic cells
DNA is stored in clumps called Chromosomes
Human
Genome
In each homologous pair,
one chromosome came from your mother
, the
other chromosome came from your father
.
These cells are now ready to become gametes!
Sections of DNA
that give
instructions for specific characters
Every human has the same genes but...
Each of us has
different versions
in
different combinations
What are Genes?
Two different types of Chromosomes
Lifecycle of a cell
Mitosis
vs.
Meiosis
What makes Meiosis special
From your daddy
From your mommy
Purpose for Crossing Over and Independent Assortment
But
why is there crossing over
during Prophase I?
And
why do chromosomes move randomly toward the different poles
during Metaphase I?
Sister Chromatids
Sister Chromatids
HomologousChromosomes
in new cells
DNA Replication
Homologous Chromosomes in old cell
Each chromosome moves to opposite ends of the cell
Sister chromatids
DO NOT
get pulled apart
Cell prepares for
cell division
Cell carries out
its functions
How to Make New Cells
First, we need to talk about DNA
DNA tells your cells what proteins to make.

DNA controls how an organism looks and functions.

So....
If you want your cells (and you!) to look and function right, you have to make sure your DNA is right.
Two types of Cell Division
Full transcript