Download Cell cycle to Sexual Reproduction

Chapter5:
The Cell Cycle and
Mitosis
The cell cycle and mitosis
happens in the nucleolus of the
cell (the dense section of
nucleus)
The Cell Cycle  A. The Role of Cell Division
Why do cells divide?
•
•
•
•
Growth
Reproduction
Replacement of dying cells – skin, RBC
Reproduction in multi-cellular organisms – gamete
formation (meiosis)
In the case of growth, why divide, rather than simply get
bigger?
•
Surface:volume ratio constraints
The Cell Cycle --> Interphase
1. G1 Phase  1st growth phase
2. S Phase  DNA duplicated
3. G2 Phase  Final growth phase
Purpose of the first three phases (Interphase) – to duplicate cell contents; 90% of
the cell’s growth cycle
4. Mitosis
Purpose of Mitosis – to divide the genetic material into exact two halves
5. Cytokinesis
Purpose of Cytokinesis – to divide all other contents (except nucleus) into two
cells
Interactive Cell cycle
• http://www.cellsalive.com/cell_cycle.htm
Create a concept map
• Use pages 153-155 to create a concept map
explaining the cell cycle.
– Start by drawing/tracing the drawing on page 153.
– Label each step with information about the step.
– Draw the arrows that separate each step and use colour
to colour in your cell cycle drawing.
– 4 marks for each step’s information (5 steps)
– 5 marks for colour and clarity.
– Due Monday /25
Important Notes
DNA wraps some special proteins to form more stable
structure called chromosomes
Chromosome are found inside nucleus
Human - 46 chromosomes, 23 pairs (1 set of 23 from egg, 1
set of 23 from sperm)
Gene is a segment of DNA that is responsible for controlling
a trait
Each chromosome contains thousands of genes (these make
up our traits)
Types of cell division
• Mitosis (this chapter):
– Growth, development & repair
– Asexual reproduction (creates identical
cells)
– Occurs in body cells
• Meiosis (next chapter):
– Sexual reproduction (yields different cells)
– Occurs in specific reproductive cells
Process of mitosis
Aim: Two identical daughter cells exact copy of mother cell
formed
Requirements – the whole DNA must be copied exactly
Phases of Mitosis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
1. Prophase
-
Chromatin condenses, this causes the chromosomes to
begin to become visible
-
Centrosomes separate, moving to opposite ends of the
nucleus
-
The centrosomes start to form a framework used to
separate the two sister chromatids called the mitotic
spindle, that is made of microtubules
-
Nucleolus disappears
2. Metaphase
- Chromosomes align on an axis called the metaphase plate
- Note: the spindle consists of microtubules, one attached to
each chromosome
3. Anaphase
- Each centromere splits making two chromatids free
- Each chromatid moves toward a pole
- Cell begins to elongate, caused by microtubules not
associated with the kinetochore
4. Telophase
•
Formation of nuclear membrane and nucleolus
•
Short and thick chromosomes begin to elongate to form
long and thin chromatin
•
Formation of the cleavage furrow - a shallow groove in
the cell near the old metaphase plate
•
Cytokinesis = division of the cytoplasm
Mitosis
Mitosis in an onion root
Asexual Reproduction
• Only one parent is
required to make offspring
• Offspring are genetically
identical to parents
• Genetically identical
organisms are called
Clones
• Mother cells create
identical daughter cells
Binary fission in bacteria
Not the best method of
chromosome division –
Cells Chromosomes replicate
then plasma membrane
grows inwards
Creates two identical daugther
cells
Happens in Bacteria
have a single chromosome
(versus the 46 human have).
Budding
• Some cells split resulting in mother and daughter cells
• Offspring is smaller than mother
• The buds grow into fully matured individuals which
eventually break away from the parent organism.
Fragmentation
• http://www.teachersdo
main.org/resource/tdc
02.sci.life.repro.asexu
al/
• In this form, the body
of the parent breaks
into distinct pieces,
each of which can
produce an offspring.
Regeneration
• In this form, if a piece
of a parent is detached,
it can grow back!
Grafting
• Used to propagate a
desired variety of tree
or shrub.
• Involves taking a twig
(scion) from a mature
plant and inserting it
into a cut stump (the
stock).
• Check it out
Vegetative Reproduction
• Method used by plants by sending a runner (underground
stems) to reproduce.
• A new plant will grow at end of each runner
• Some plants use other underground stems called rhizoids,
bulbs, or tubers to reproduce asexually.
Spore Production
• Some fungi and plant
species release cells called
spores
• Spores reproduce new
organisms via mitosis
• Spores can be carried by
water, wind or animals.
• Video
Asexual Reproduction
Advantages
Disadvantages
• Large number of offspring
produced quickly
• Large colonies can form
• Large numbers or
organisms may survive
• No energy is required to
find a mate
• Offspring are clones, no
differences and if
mutation occurs.. Uh oh!
• Too many individuals may
fight with each other to
survive
• Entire colonies can be
wiped out if not adapted to
environment
Asexual Reproduction Questions
• Use notes and handout
to answer questions
• Work in partners
Cloning Assignment
• Read pages 176-77
• What is the difference
between reproductive
(DNA) and theraputic
cloning (stem cells)?
• Do you have a
problem with either?
• Make notes for a
discussion….
• Do you find them
morally wrong?
Reproductive Cloning
Duplicate existing organism by removing nucleus of egg cell
and fusing with mammary gland cells
Theraputic Cloning
Embryonic Stem cells grown into desired organs
What is Sexual Reproduction?
• Genetic information from
two parents passed on to
offspring
• Both parents make special
cells called gametes
• Gametes contain only one
set of chromosomes
• (sperm and egg)
• When two gametes
come together (ask
your parents) this is
called fertilization
and form a new cell
called a Zygote
• A zygote will mature
and undergo mitosis to
become an embryo.
Diploid vs. Haploid
• Diploid (Di = two)
• Every cell in body
except gametes
(sperm/egg)
• Contain 2n or two sets
of chromosomes
• 2 sets of 23 = 46
chromosomes
• Haploid
• Gametes (sperm and
egg)
• Contain n or one set
of chromosome
• 23 chromosomes
How do cells become Haploid?
• Meiosis….
Meiosis – key differences from
mitosis
• Meiosis reduces the number of chromosomes by half.
• Daughter cells differ from parent, and each other.
• Meiosis involves two divisions, Mitosis only one
• End product is 4 haploid cells (1n) instead of 2 diploid
cells (2n)
• Occurs only in sex cells to produce gametes (sperm and
egg)
Methods of Genetic Variation
Crossing Over:
During Meiosis 1 nonsister chromatids will
exchange genetic
information.
Independent Assortment
Different combinations of
chromatids can end up in
each gamete (egg and
sperm cells)
Animation
Meiosis 1
First division of meiosis
• Prophase 1: Each chromosome duplicates and remains
closely associated. These are called sister chromatids.
Crossing-over can occur during the latter part of this stage.
• Metaphase 1: Homologous chromosomes align at the
equatorial plate. (Tetrads or two full chromosomes pair up)
• Anaphase 1: Homologous pairs separate with sister
chromatids remaining together.
• Telophase 1: Two daughter cells are formed with each
daughter containing only one chromosome of the
homologous pair
.
Meiosis II
Second division of meiosis: Gamete formation
• Prophase 2: DNA does not replicate.
• Metaphase 2: Chromosomes align at the
equatorial plate.
• Anaphase 2: Centromeres divide and sister
chromatids migrate separately to each pole.
• Telophase 2: Cell division is complete.
Four haploid daughter cells are obtained.
Mitosis vs. meiosis
Meiosis vs Mitosis
Mitosis
Meoisis
mitosis produces daughter cells
identical to parent cell. No genetic
variation
Meiosis creates: genetic Variation
1 cycle
2 cycles
2 diploid cells created
4 haploid cells (gametes) result
Both diploid cells are identical
All four haploid cells are different
from each other and different from
parent cells
All cells (except sex cells)
Truly unique offspring will be created
when male and female gametes meet
(Sperm and egg)
Only in sex cells (sperm and egg)
Review….What is Meiosis?
• Type of cell division that halves number of
chromosomes (e.g., 2N to 1N)
• Process of 2 successive divisions
• Product is gamete, essential for sexual
reproduction
A comparison of mitosis and meiosis: summary
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
Chromosome Mutations
• Gene mutations may have no effect on
organism because they are small differences
in genetic information
• When big chunks of DNA are lost,
duplicated or moved within a chromosome
or to an chromosome during Meiosis the
result can be drastic
• Chromosome mutations also occur from
mutagens.
• Fruit flies can grow legs where their
attenae’s should be, eyes growing out of
their wings etc…
Where mutations occur?
• Whole mutations can occur during Meiosis
I when homologous chromosomes (tetrads)
fail to separate or in Meiosis II when sister
chromatids fail to separate.
• One gamete will have two copies of
chromosome while the other will have none.
• Do you think these chromosomes are
genetic? Think about the result in people
when chromosomal mutations occur?
Chromosome Mutations
• Down Syndrome
– Chromosome 21 does not
separate correctly.
– They have 47
chromosomes in stead of
46.
– Children with Down
Syndrome develop slower,
may have heart and
stomach illnesses and vary
greatly in their degree of
inteligence.
Chromosome Mutations
• Cri-du-chat
– Deletion of material on 5th
chromosome
– Characterized by the cat-like
cry made by cri-du-chat babies
– Varied levels of metal
handicaps
Sex Chromosome Abnormalities
• Klinefelter’s Syndrome
–
–
–
–
–
XXY, XXYY, XXXY
Male
Sterility
Small testicles
Breast enlargement
Sex Chromosome Mutations
• Turner’s Syndrome
– X
– Female
– sex organs don't
mature at adolescence
– sterility
– short stature
Sex Chromosome Mutations
• XXX
–
–
–
–
–
–
Trisomy X
Female
Little or no visible differences
tall stature
learning disabilities
limited fertility
Karyotypes
• Geneticists can prepare a
picture of one’s
chromosomes called a
Karyotype
• Take chromosomes during
mitosis, cut and paste them
and paired by size.
• When analyzing, geneticists
can determine mutations and
treatment for genetic
disorders or syndromes
• Syndrome is a disease with
a specific group of
symptoms that occur
together (down’s syndrome)