Transcript Unit 7 – Section 8.2 Mitosis

Unit 7 – Section 8.2 Mitosis
 When an organism grows larger it is because they
are adding more cells. Their cells generally remain a
constant size.
Reasons for Cells to Remain Small
Diffusion
- Diffusion occurs at a specific speed, the further
substances have to go the longer it takes.
DNA
- Nucleolus cannot keep up with the demand to copy
off instructions for all the new organelles.
Surface Area to Volume Ratio
- The inside volume of a cell increases faster
than the outside surface area. The inside
(volume) needs more nutrients than the outside
(surface area) can let in or out.
 No living organism or cell lives forever. They
must reproduce in order for life to carry on
(Cells come from pre-existing cells).
Reasons for Cells to Reproduce
Growth
- One of the characteristics of life is that all
organisms grow or develop over time. New
cells are necessary for this.
Replace / Repair
- Cells are dying and being damaged
continually, therefore they must be replaced.
Diffusion
- Cells become too big to function efficiently
(Nutrition & Excretion)
Unit 7 – Section 8.2
DNA Terminology
Chromatin
- What the DNA is called when it is uncoiled and
not easily visible (Its normal state – Interphase)
Chromosome
- What the DNA is called when it is coiled and
visible (During Mitosis & Meiosis)
Chromatids
- What each half of a double stranded
chromosome is called
Terminology continued . . .
Replication
- The process that copies and makes an exact
replica of all DNA strands (makes them
double stranded – Interphase)
Centromere
- The part where the two chromatids are held
together. It holds the two identical strands
together so they form an “X”.
Type of
Cell
# of DNA
Strands
# of
Homologues
Somatic
Body Cells
46
23
Gamete
Sex Cells
23
NONE
# of
Sets Names
2–
Diploid
1–
Haploid
1. The weeds in this garden are spreading rapidly. What effect
might this have on the flowers in the garden?
2. Suppose a change in a cell’s genes causes the cell to
reproduce very rapidly. How might this increased rate of
reproduction affect surrounding cells?
Cell Division - Mitosis
 Cells reproduce by dividing in half.
 The division of chromosomes (DNA) is called
Mitosis
 The division of the cytoplasm & the cell is call
Cytokinesis
* A cell’s life is continuous and follows a cycle
that repeats itself
* The Cell Cycle includes 3 Stages that
repeatedly follow each other:
Interphase – Mitosis – Cytokinesis
 Cells will grow as they live, double all of their
internal parts (organelles), and split or divide
equally into 2 Daughter Cells
 The Daughter Cells will repeat this process and
so will the next generation.
 This is the basis of the cell cycle.
* Different cells go through the Cell Cycle at
different rates
* Minutes – Hours – Days – Weeks – Month -Year
Interphase
 The cell spends over 90% of its life carrying
out its Normal Functions.
* This is also a Preparation time for the cell to
get ready for Mitosis
 Cell grows in size
 Replication occurs = This is the doubling of all
the DNA (DNA becomes “X” shaped).
 The organelles (Cytoplasm) is doubled.
* With out doubling the size – DNA – Cytoplasm
we would end up with 2 half cells that could
not function
Mitosis
Prophase (1st Phase)
 The Chromatin (DNA) is coiling up and becoming
visible Chromosomes.
 The Nuclear Membrane & Nucleolus dissolve and
disappear.
 The Centrioles move to opposite ends of the cell.
 Microtubules & Microfilaments form fibers which
create the Spindle.
* The Pathway for the Chromosomes to follow.
Metaphase (2nd Phase)
 The spindle and its fibers move the
chromosomes so they are lined up in the middle
of the cell between the centrioles.
 The spindle fibers attach the chromosomes to
the centrioles.
* The place on the chromosome where the spindle
fibers attach is the centromere.
Anaphase (3rd Phase)
 The centrioles on each opposite end of the
cell pull on the centromeres.
 They divide and each chromatid is pulled in
an opposite direction.
* This is very rapid and is the shortest phase.
Telophase (4th Phase)
 The two clusters of chromatids on each side
of the cell start to unwind and become
chromatin again.
 A new nuclear membrane starts to form
around the DNA clusters.
 The spindle fibers disappear.
* This phase is almost the opposite of Prophase
Cytokinesis
* This takes place immediately after Mitosis.
 The cell elongates and starts to pinch in the
middle.
 The cytoplasm divides itself as organelles are
separated to opposite sides.
* In plant cells a new cell wall forms down the
center dividing the cell in half.
 Once the cell has divided into two, they are
both in interphase and start the process over.
Importance of the Cell Cycle
(Mitosis & Cytokinesis)
 All organisms start out as a single cell, this
allows for Growth.
 In Humans, cells naturally die off at a rate of
approximately 50 million a second.
Therefore, these need to be Replaced.
 Injury and disease can cause extra cell loss
that needs to be replaced as well.
Mitosis Phases
12--White Pipe Cleaners are Chromosomes
2-- Tan Yarn is Nuclear Membrane
2-- Wooden Spools are Centrioles
12-- Red Yarn is Spindle Fibers
4-- Construction Paper is Organelles
* Using these parts show the stages of Mitosis
in an Animal with 4 Total Chromosomes (2
Pairs)
Meiosis
 A process of Nuclear (Chromosome) Division
creating daughter cells with the haploid (1 set)
number of chromosomes.
 Meiosis is used to create Gametes Only.
Male Gamete = Sperm
Reproductive Cells
Female Gamete = Egg
 Meiosis only occurs in the Reproductive Organs
(Gonads). Mitosis occurs throughout the entire
body.
Male Gonad = Testes
Reproductive Organs
Female Gonad = Ovaries
 Gametes must contain the Haploid # of
Chromosomes so when they unite the new
individual will contain the correct information
( 23 Sperm + 23 Egg = 46 New Individual )
 All cells in the Body contain the Diploid # (2 sets)
of Chromosomes.
 Meiosis is used to create Gametes from these cells
** Meiosis makes Gametes in the Gonads
 Meiosis has two separate divisions ( I & II ) and will
create four individual cells.
Human Female Karyotype
Human Male Karyotype
Mitosis
Purpose:
Make new cells or replace
worn out cells
Where:
Throughout the entire
organism (anywhere cells
are needed– Somatic Cells)
Genetic Significance:
The products (daughter
cells) are identical to each
other and to the cell they
originated from. Therefore
they are clones.
Meiosis
Purpose:
Make gametes (sperm &
egg cells)
Where:
Reproductive Organs
(ovaries & testes—
Gametes)
Genetic Significance:
The products (sperm & egg)
are genetically different
from each other, the
genetic material is
rearranged during and
after meiosis (end product
has genetic variation)
Mitosis
 Occurs everywhere in the




body (Somatic Cells)
End up with 2 Diploid Cells
Identical to the Parent Cell
Has only 1 Division
Mitoisis is part of a
repeated Cell Cycle
All Chromosomes move
independently
Meiosis
 Occurs only in the Gonads




(Gametes)
End up with 4 Haploid Cells
Different from the Parent
Cell
Has 2 Divisions
Meiosis is a one time
process for a cell
Synapsis occurs and forms
Tetrads (Prophase I )
Meiosis I
 This first division of DNA separates the
Homologous Chromsomes
(Diploid 2 sets  Haploid 1 set)
Interphase
- Replication occurs = Doubling of the DNA
(single strands become double “X”)
* There is no growth or doubling of the cytoplasm
like Mitosis. These cells have no “normal function”
except to be turned into Gamates.
Prophase I
- Chromatin is coiling up and becoming visible as
Chromosomes.
- Nuclear Membrane & Nucleolus dissolve &
disappear.
- Centrioles move to opposite ends of the cell.
- Spindle fibers start to form.
* Chromosomes find their homologue and pair
up, forming a Tetrad, this is called Synapsis.
Metaphase I
- The spindle fibers move the Tetrads
(Homologous Pairs) toward the middle of the cell
in a line.
- The spindle fibers attach one chromosome to
one centriole and the other chromosome to the
other centriole.
Anaphase I
- Each centriole pulls one chromosome of the
Tetrad in opposite directions.
( The two sets are being divided )
Telophase I
- Two clusters of chromosomes form on each end
of the cell & a new nuclear membrane forms
around each.
- Chromosomes may uncoil forming Chromatin
- Spindle fibers disappear.
Cytokinesis I
- The cell elongates and starts to pinch together
in the middle.
- The cytoplasm is divided into two separate cells
- Males: Equally but with only ½ the normal
amount.
- Females: Unequally, one cell gets all of the
cytoplasm.
Meiosis II
 This 2nd Division separates the Chromatids “X’s”
of the remaining chromosome
 There is no real Interphase between Meiosis I
and Meiosis II (No growth – Replication – or
Organelles made).
 Both cells from Meiosis I go through Meiosis II
 Prophase II, Metaphase II, Anaphase II, &
Telophase II are basically the exact same as
Mitosis.
 The only real difference is the chromosome #
is already Haploid and Organelle #’s are
different.
 End result is 4 Cells, each with only 23
(Haploid) Single-Stranded Chromosomes.
They are now Gametes.
 Spermatogenesis
46 Interphase
II
Oogenesis
46
XX
46
II
Interphase
Meiosis I
23
X
Meiosis I
23
X
23
I
23
I
23
X
23
X
Meiosis II
23
I
46
XX
Meiosis II
23
I
4 Haploid
Gametes
23
I
23
I
1 Haploid
Gamete
23
I
23
I
3 Polar
Bodies
Unit 7 – Section 10.2
 Forming Tetrads in Synapsis causes two genetic
events to occur, they are Crossing Over and NonDisjunction
Crossing Over
- Happens in Prophase I of Meiosis.
- When parts of Homologous chromosomes switch
from one chromosome to the other (Information
from the maternal chromosome is placed on the
paternal chromosome and vice versa).
- Crossing over causes more variety in the
offspring because it switches information
around between homologous chromosomes
* It is estimated that there are 2-3 cross overs per
pair of chromosomes during each Prophase I
Non-Disjunction
- Happens in Anaphase I of Meiosis.
- Failure of the Homologous chromsomes to
separate properly.
- One of the spindle fibers break and the whole
tetrad is pulled to one side.
- The result is gametes that have either 22 or 24
chromosomes. The zygotes that result from
these gametes will have 45 or 47 chromosomes
(usually the zygote doesn’t live)
** It causes Genetic Disorders or conditions
that usually have a negative developmental
effect such as:
Down Syndrome
Turner’s Syndrome
Jacob’s Syndrome
Patau’s Syndrome
Metafemales
Klinefelter’s Syndrome