Cell division
Mitosis & Meiosis
Cell Review
• Cells have DNA, the information needed for
life.
• DNA is packaged into something called
chromosomes.
Cell division
All complex organisms
originated from a single
fertilized egg.
Through cell division the
numbers are increased
Cell then specialise and
change into their various
roles (blood cell, bone
cell, nerve cell, etc)
Why do cells divide?
• Growth
• Reproduction
• Replacement of dying cells – skin,
blood cells
Cell division in prokaryotes:
Binary fission
Bacteria have a single
chromosome (versus the 46
humans have).
1.Chromosomes replicate
2.Cell membrane pushes inward
3.Cell divides in two,
each with a chromosome
Types of cell division in Eukaryotes
• Mitosis:
–Growth, development & repair
–Asexual reproduction (yields identical
cells)
–Occurs in somatic (body) cells
–Produces 2 identical cells
• Meiosis:
–Sexual reproduction (yields different
cells)
–Occurs in reproductive cells (gametes)
A comparison of mitosis and meiosis
Paper Plate Models
• Each group will be in charge of making a paper
plate model of mitosis.
• Each person will find mitosis in the book and
model each stage on a paper plate with yarn.
– Yarn will represent the chromosomes.
• Then the cell stages will be strung together to
make a cell mobile.
Example
• Write the name of the
phase in back of the
plate
–
–
–
–
–
Interphase
Prophase
Metaphase
Anaphase
Telophase
Mitosis
• All daughter cells contain the same genetic
information from the original parent cell from which
it was copied.
• Every different type cell in your body contains the
same genes, but only some act to make the cells
specialise into nerve or muscle tissue.
Mitosis overview
Parent cell
Chromosomes are
copied and double
in number
Chromosomes
now split
2 daughter cells
identical to original
Mitosis
First step
• Interphase begins first.
– Chromosomes are copied
– Chromosomes appear as thread (chromatin)
1. Prophase
Mitosis begins
- Chromatin (DNA thread)
condenses, causing the
chromosomes to begin to
become visible (X’s).
- Centrioles appear and
begin to move to
opposite ends of cell.
- Spindle fibers, made of
microtubules, form
between the poles
- Nucleolus disappears
2. Metaphase
Chromosomes align
on an axis called the
metaphase plate
- Chromatids (or pairs
of chromosomes)
attach to the spindle
fibers
-
3. Anaphase
- Chromatids (or pairs of chromosomes)
separate at the centromere (center) and
begin to move to opposite ends of the cell
- Cell begins to elongate
4. Telophase
•
Formation of nuclear membrane and nucleolus
Two new nuclei form
Chromosomes appear as chromatin (threads rather
than rods)
Mitosis ends.
Formation of the cleavage furrow - a shallow groove in
the cell near the old metaphase plate
Cytokinesis
• Division of the cytoplasm
• AT THE END the daughter cells have the
SAME number of chromosomes as the
PARENT/MOTHER cell.
Mitosis Flip Book
• You will complete each page to illustrate the
changes that take place in a cell during cell
division.
• The first oval (or ovals) in EACH phase should
show the location of the organelles at that stage.
• Use the extra ovals to show the movement of
organelles between stages.
• Write a brief description of each stage on the blank
side of your page. Interphase is the
Interphase
stage where….
Mitosis Animated
animation
Mitosis
Mitosis in an onion root
Can you identify some of the stages of Mitosis here?
Interphase
Anaphase
Metaphase
Prophase
Meiosis
• Type of cell division that halves number of
chromosomes
– 1N is one chromosome
– 2N is two chromosome (sister chromatids)
• 2 divisions involved
• Product is gamete, essential for sexual
reproduction
1N
2N
Terms
• Homologous Chromosome: a chromosome that has
the same DNA (ex: 2 of the same chromosomes that
hold the DNA for hair color and eye color.)
• Crossing over: when the chromosome from the male
and from the female swap DNA.
Overview of meiosis: how meiosis reduces chromosome number
First
part
of
meiosis
In
I, I,
Homologous
chromosomes
Second part
In Prophase
Metaphase
Homologous
chromosomes
involvescross
separating
over
andto
swap
line
up next
eachDNA.
other
involves separating
This allows diversity in offspring.
homologous chromosomes chromatids
Homologous
Same chromosome
Overview of meiosis: how meiosis reduces chromosome number
First part of meiosis
Second
part
In Anaphase
InI,Telophase
Homologous
I, Homologous
chromosomes
chromosomes
involves
separating
Are pulled
areapart.
in separate cells.
involves separating
homologous chromosomes chromatids
homologous
Overview of meiosis: how meiosis reduces chromosome number
First part of meiosisIn Telophase II,Second
each of thepart
4 daughter cells
In Prophase
In II,
Anaphase
is have
no
II, chromatid
separates,
Inthere
metaphase
II,
should
one copy(2N)
of each
chromosome.
involves
separating
REPLICATION
moving
or Cells
Crossing
one
chromosome
over.
(1N)
cell.
involves
separating
Chromosomes
line
in the
2 cells.
areup
NOT
identical
dueper
to
crossing
over
homologous chromosomesandchromatids
swapping DNA.
The results of crossing over during meiosis
• Crossing over helps to
promote genetic variation.
• Two homologous
chromosomes can code for
the same traits, but the
variety in the traits may be
different.
– Example: single gene controls
the color of flower petals, but
there may be several different
versions of the gene.
Evolutionary advantage
• asexual reproduction (mitosis)
– easy, rapid, effective way to reproduce
– useful in stable environment
– lack of genetic diversity among offspring
• sexual reproduction (meiosis)
– promotes genetic variability
– useful in changing environment