Chapter 5 Cell Division 2003v
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Transcript of Chapter 5 Cell Division 2003v
Biology…is about us
…is about living things
…is about animal
…is about plant
Do you remember…during form 1
You have learnt about …
Cell is basic unit of life
Now we will learn new topic
Do you ready to start our lesson?
5.1 Mitosis 5.2 Meiosis
5.3 Appreciating
Watch the video carefully...
Pea plant movie
What about this picture???
allStagesButtons.gif
This is we called as...development
• What process or even occur which allow all of these happen????
Cell divison
CHAPTER 5:
Today we will learn about
5.1 mitosis
The necessity for cell division in living organism
What is chromosome?
The significance of mitosis
The necessity for cell division in living organism
• All living organism consist of cell
– Most of cell undergo cell division
Cell Division- mitosis
...splitting cell into two daughter cell which genetically identical to parent cell
Parent cell
Daughter cell
Why do cells divide?
• _______
• _______• _______
• _______
The cell divide for...
• The new cell formation allow:• replacement of dead cell
• body repair damaged tissue
• body growth and development
• reproduction in unicellular organism
Types of cells
– Somatic cell- all body cell (except reproductive cell) form trough mitosis
– Gametic cell- reproductive cell that formed trough meiosis
What is chromosomes
• The nucleus of cell contain chromosomes
• Each chromosomes contain DNA molecules which carries genes (genetic material)
• Genes- determine the individual characteristic of organism
DNA
Number of chromosomes
• The chromosomal number for certain species is constant and varied from one species to another.
Eg: human - 46 chromosomes
• Monkey- 48 chromosomes• Chicken- 78 chromosomes
Somatic cell – has two set of chromosomes. One set is inherited from each parent.
Two set of chromosomes = diploid= 2n
Gametic cell – has one set of chromosomes.
One set of chromosome=_______=_____
Gametic cell – has one set of chromosomes.
One set of chromosome=_______=_____
Diploid organisms receive one of each type of chromosome from female parent (maternal chromosomes) and one of each type of chromosome from male parent (paternal chromosomes)
Ploidy – refers to the number of sets of homologous chromosomes in a cell
● ______ – one copy of each chromosome
– designated as “n”
● ______ – two copies (= pair) of each chromosome – designated as “2n”
• In human (46 chromosomes in somatic cell)• Each set consist of _____ chromosomes
• the nucleus of human somatic cell has ______ chromosomes arranged in _____ pairs or 2n = ______ chromosomes
• Gametes contain only one set of unpaired chromosomes or haploid number of chromosomes (n)
2set (2n-diploid): ___ chromosomes (somatic cell)1set (n-haploid):___ chromosomes (gametic cell)
Trivia....
• A monkey sperm cell have 24 chromosomes, how many pairs of chromosomes does the cheek cells of the monkey have?
Homologous chromosomes
• Two chromosomes in each pair have the same structural features and are referred as the homologous chromosomes.
Homologue
• One form paternal origin whereas the other one is from maternal origin
Homologous Chromosomes
Homologous vsDuplicated
Karyotype
Significances of mitosis
• Each daughter formed through mitosis carries genetic material (DNA) inherited from the parent cell.
• This genetic information is passed on to new cells during division to produce two identical nuclei.
The important of mitosis
1. growth- the number of cell within organism increases by mitosis. Basic grow in multi cellular organism
Growth in human
2. cell replacement- replacement damaged cells and tissue
• 3. Regeneration – some animals are able to regenerate whole part of the body such as star fish, lizard tail
• 4. asexual reproduction – mitosis is the basis of asexual reproduction individual of species by one parent
What you need to know about cell divisions?
• What happen before division?
• What is chromosome, centromer, centriole, sister chromatids and homologous chromosome?
Packing for the move…
When cell is not dividing… ● DNA molecules in extended, uncondensed form = __________
● Cell can only use DNA to produce molecules when in extended state.
When cell is preparing for division…
● DNA molecules condense to form ______________ prior to division.
– each chromosome is a single molecule of DNA
– easier to sort and organize DNA into daughter cells
Structure of a eukaryotic chromosome
• __________ chromosome
arm armcentromere
Prior to cell division:• chromosomes (DNA) are replicated (duplicated)
duplicatedchromosome
• duplicated chromosome – attached at their centromeres – as long as attached, known as _________ ______________
daughterchromosomes
sisterchromatids
Karyotype• Karyotype is the ______
______ ___ _________ of a cell of any living organism.
• The chromosomes are arranged and displayed (often on a photo) in pairs, ordered by size.
• To the right is a typical karyotype of a human male.
arm armcentromere
Karyotype
Haploid, Diplod, Homologous, Replicated, Duplicated, Chromatids, Chromosomes…
What do you understand about development??? What happen to cell?
What is cell division?
allStagesButtons.gif
Cell cycle
Cell Cycle
2 major phases:
• __________ (3 stages) – DNA uncondensed (= chromatin)
• ________ (4 stages + cytokinesis)- Nuclear division & division of cytoplasm
– DNA condensed (= chromosomes)
My idea
• Before we continue, I want all of you to draw the cell in interphase phase base on you understanding
Interphase
non-dividing state
3 sub-stages:
___ – cell grows in size – organelles replicated
___ – replication of DNA – synthesis of proteins associated with DNA
___ – synthesis of proteins associated with mitosis
My idea (2 minutes)
• Base on the cell given, draw the cell in each sub phase base on your understanding
Mitosis 4 sub-phases:
1st – Prophase
2nd – Metaphase
3rd – Anaphase
4th – Telophase and Cytokinesis
ACTIVITY: JIGSAW1. Teacher will count student from 1 until
5 then it will be repeating until all of student finish
2. then all of you will sit in group and get the subtopic to be discuss from teacher.
3. after finish discussion in group (10 min), you need to distribute into another group and explain about the subtopic you get until they understand.(5 min)
Stages in Mitosis
PROPHASE
• Chromosomes in the nucleus condense and become tightly coiled. They appear shorter and thicker
• Each chromosomes consist of a pair of sister chromatids joined together at the centromere.
Prophase:nucleus disappears
centrioles migrate
chromosomes appear
METAPHASE
• Begin when centromere of all chromosomes are line up on the metaphase plate
• Two sister chromatids are attached the fibres by their centromere.
centriole
centromereSister chromatids
Spindle fibre
ANAPHASE
• Two sister cromatids of each chromosomes separate at the centromere
• Sister chromatid are pulled apart to the opposite pole by the shortening of spindle fibre.
anaphase
TELOPHASE• Begin when 2 set of
chromosomes reach the opposite pole of the cell.
• The spindle fibre dissapear and a new cell membrane form around each set of chromosomes
• Nucleolus also form in each of nucleus
• Chromosomes start to uncoil (chromatin)
APPLY YOUR IDEASAPPLY YOUR IDEAS
1. Answer all the objective question (individually)
2. I will call a number to write down the answer in front of class.
Lets plaaaay…
“Guess That Phase!”
Activities (20 MINUTES)Activities (20 MINUTES)
• Made model of MITOSIS using drawing paper, thread and plasticine in group of 5
• The chromosome number is 2n=2
• Made sure your model has the 4 phase of mitosis and show the daughter cell at the last.
Summary-Phases and Sub-phases of Cell Division
1. Interphase
2. Mitosis
a. G1
b. S
c. G2
a. Nuclear division
b. Cytokinesis
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
DEMOs: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html#
http://www.cellsalive.com/mitosis.htm
5.1 Mitosis
•Cytokinesis•Controlled mitosis
•Uncontrolled mitosis
Centrioles
Chromatin
Interphase
Nuclear envelope
Cytokinesis
Nuclear envelope reforming
Telophase
Anaphase
Individual chromosomes
Metaphase
Centriole
Spindle
CentrioleChromosomes
(paired chromatids)
Prophase
Centromere
Spindle forming
Go to Section:
Do you still remember this phase
Centrioles
Chromatin
Interphase
Nuclear envelope
Cytokinesis
Nuclear envelope reforming
Telophase
Anaphase
Individual chromosomes
Metaphase
Centriole
Spindle
CentrioleChromosomes
(paired chromatids)
Prophase
Centromere
Spindle forming
Go to Section:
Centrioles
Chromatin
Interphase
Nuclear envelope
Cytokinesis
Nuclear envelope reforming
Telophase
Anaphase
Individual chromosomes
Metaphase
Centriole
Spindle
CentrioleChromosomes
(paired chromatids)
Prophase
Centromere
Spindle forming
Go to Section:
Centrioles
Chromatin
Interphase
Nuclear envelope
Cytokinesis
Nuclear envelope reforming
Telophase
Anaphase
Individual chromosomes
Metaphase
Centriole
Spindle
CentrioleChromosomes
(paired chromatids)
Prophase
Centromere
Spindle forming
Go to Section:
Centrioles
Chromatin
Interphase
Nuclear envelope
Cytokinesis
Nuclear envelope reforming
Telophase
Anaphase
Individual chromosomes
Metaphase
Centriole
Spindle
CentrioleChromosomes
(paired chromatids)
Prophase
Centromere
Spindle forming
Go to Section:
Share your idea!!
You now that cell will divide into two daughter cell but how the cell will divide after the telophase????
You now that cell will divide into two daughter cell but how the cell will divide after the telophase????
How cell divide?
• 1.
• 2.
• 3.
• 4.
ACTIVITY: JIGSAW1. Please sit in group of five or four
2. Discuss in group the subtopic given in task sheet
3. after finish discussion in group (10 min), you need to distribute into another group and explain about the subtopic you get until your friends understand(5 min)
Cytokinesis:
• Cytoplasm of the cell and its organelles separate into 2 new daughter cells
• In animals, a groove called the cleavage furrow forms pinching the parent cell in two
• In plants, a cell plate forms down the middle of the cell where the new cell wall will be
What can limit cell growth?
• Think about what can limit your growth
• Hmmm….think about an ant, a tennis ball, and a basketball
• Space– Surface/volume ratio
• What could happen if cells continue to grow without any limits?
Cancer
• Cancer is one of the most common diseases in the developed world:
• 1 in 4 deaths are due to cancer• 1 in 17 deaths are due to lung cancer• Lung cancer is the most common cancer in men• Breast cancer is the most common cancer in
women• There are over 100 different forms of cancer
Cancer
• The division of normal cells is precisely controlled. New cells are only formed for growth or to replace dead ones.
• Cancerous cells divide repeatedly out of control even though they are not needed, they crowd out other normal cells and function abnormally. They can also destroy the correct functioning of major organs.
DNA mutations disrupt the cell cycle.
Mutations may be caused by:
1. radiation 2. smoking 3. Pollutants 4. chemicals 5. viruses
What can cause cancer?
1. a chemical in the coal dust caused damage to genes that regulate the cell cycle.
• Pott was probably the first person to associate a specific type of cancer (scrotal cancer) with a specific occupation (chimney sweeping).
• Pott believed the problem was the coal soot that caught in the skin folds of the scrotum. In 1918, coal tar was shown to cause skin cancer in rabbits, and in 1924 the causative agent was identified as polycyclic aromatic hydrocarbons, especially benzo (a) pyrene.
2.X-rays damages genes that regulate the cell cycle.
• Ionizing radiation is a well-known human carcinogen. The first reports of association between X-rays and cancer appear in the literature in the early 1900s.
• cancer developed among painters of luminescent dials in watch factories in the 1930s
• and radiation from nuclear tests and cancer (for example, children in the Marshall Islands exposed to radioactive iodine released from a nuclear test displayed a significant increase in thyroid cancer).
3.exposure to UV light damages genes that regulate the cell cycle.
• The relationship between sun exposure and skin cancer has been clarified greatly across the past century.
• In the late 1800s, observers noticed that sailors exposed to the sun developed a variety of abnormal lesions called "sailor's skin," and in the early 1900s, an increased risk of skin cancer was observed among farmers.
• By 1928, researchers had demonstrated the carcinogenic effect of UV radiation on the skin of laboratory animals. Today, scientists recognize excessive exposure to UV radiation (whether from the sun or other sources) as a key risk factor for skin cancer.
While normal cells will stop dividing if there is a mutation in the DNA, cancer cells will continue to divide with mutation.
TumoursTumours
Abnormalities can sometimes occur in cells which reproduce at a rapid rate, this in turn may lead to the formation of tumours.
Tumours of any type should be considered serious.
Although benign tumours do not usually cause a threat to a persons life, they can cause great inconvenience if not treated.
Applying your idea• Individually, answer all this question.
• Submit the answer at the end of the class.
Cytokinesis? (10 minutes)
• How cytokinesis occurs in animal cells?• How cytokinesis occurs in plant cells?• How many new cells formed? The new cells called as?• Compare size of new cells to each other?• Compare size of new cells & parent cell?• Daughter cells & parent cell genetically identical or
different? Give reason to your answer.
Controlled and uncontrolled mitosis (15 minutes)
• what is defined as controlled mitosis?
• Why the rate and timing of cell division important?
a._______________________b_______________________c_______________________• What cell continue divide throughout our life? • What cell do not divide at once they mature
• what is defined as uncontrolled mitosis?
• What factor can cause uncontrolled mitosis?
• What is tumour?
• What is benign tumour? Do benign tumour is dangerous?
• What is malignant tumour?
• Can cancer cell spreads through our body? If yes, how the cancer cell spreads?
Aplication of mitosis
The story story…
• You are a scientist which explore the forest to find out a rare plant species. One day, you find the plant after few month you are doing research in the forest. However, the people there not allow you to take out the plant out from the place but they allow you to take the piece of the meristem tissue of the plant. What can you do with the tissue so that you are able to replant and commercialized the plant.
Do you have watching this movie???
Or this???
• What do you know about
Cloning?
Chapter 5: Cell division
Mitosis- APPLICATION OF MITOSIS
Cloning
• Asexual organism reproduce clones.
• Clone has same genetic content and chromosomal number
• Cloning is the process to produce genetically identical organism
Cloning in plant
• Technique of cloning plant known as tissue culture
Tissue culture laboratory
How to do tissue culture?
Animal cloning
• Definition: The process of making identical genomic copies of an original animal.
Brief History of Cloning• 1952: Briggs and King clone tadpoles.
• 1953: Watson and Crick find the structure of DNA.
• 1962: John Gurdon clones frogs from differentiated cells.
• 1963: J.B.S. Haldane coins the term ‘clone’.
Brief History of Cloning• 1977: Karl Illmensee creates mice with
only one parent,
• 1984: Twinning- create genetic copies from embryonic cells.
• 1996: First animal cloned from adult cells is born.
The Cloning Process• 1978: Splitting embryos
• 1986: Embryo Cloning
• 1994: Embryonic cell line cloning
• 1996: Adult or Somatic cell cloning
Step of cloning-Stage 1
Cell collected from a sheep’s udder.
Stage 2
Nucleus is removed from unfertilized egg of second sheep.
Stage 3
Udder cell is inserted into egg with no nucleus.
Stage 4
Insertion is successful.
Stage 5
Electrical charge is supplied.
Stage 6
Cells begin to divide.
Stages 7 & 8
Dolly The SheepDolly The Sheep
Hello DollyDolly was the first mammal cloned from an adult cell.
She was born in 1996 and died in 2003.
She was 6 when she died, about half the usual age for a sheep
From National Geographic
• Scientists in Texas have successfully cloned a cat, opening the way to replicating pets and other valued animals once the technique is perfected.
The kitten, called CC (the old typist's abbreviation for carbon copy) and now almost two months old, appears healthy and energetic, although she is completely unlike her tabby surrogate mother, Mark Westhusin and colleagues at Texas A&M University, College Station, announce in the February 21 issue of Nature.
Read more on
• http://news.nationalgeographic.com/news/2002/02/0214_021402copycat.html
Advantages of cloning
• 1st presenter (5-7 minutes only)
Disadvantages of cloning
• 2nd presenter (5-7 minutes only)
Apply your idea
• Now divide yourself into 2 group
• Pro and con group
• Read the situation carefully
• Debate the situation by state the advantages and disadvantages of the cloning in this situation.
Situation
• A country use cloning to culture the a species of tomato. This clone species widely use throughout the country because there are big and have good taste. Government urge all farmer to grow this species of tomato and prevent other tomato species to be plant. Do you agree with this decision???
Conclusion
• Scientist and government group
• Farmer group
30 Cloned Human Embryos
• U.S. and South Korean scientists have cloned 30 human embryos. They said that this is a 'major step forward' in curing currently incurable diseases. The thirty human embryos each contain stem cells that can be used to create almost any human tissue. Diseases such as diabetes and muscular dystrophy damage this tissue.
Hargailah masa kerana masa itu berharga…
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This man and this woman had been marry years ago. Can you imagine the face or appearance of their child?
Do you think their child has exactly same face with their parent?
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Do you thinks they are brothers?Give reason to your answer.
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The answer is yes …
• They are brothers…
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They are…
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Sheikh Ahmad Shukor; Sheikh Taufik Shukor; Sheikh Mustapha ShukorSheikh Arwiz Shukor.
- Do you have exactly same appearance or face with your mother or father or sister or brother (except you are twins) ?
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• What happen if all cell in your body include reproductive cell only undergo mitosis?
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Objectives:
• State necessity of trait inheritance to continue life
• State necessity maintain diploid no. of chromosomes over generation
• State significance of meiosis
• Identify type of cell undergo meiosis.
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Necessity of trait in heritance in offspring
• All individual in same species have same chromosomal number.
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• If mitosis only the way cell can divide- each gamete will get a complete set of chromosome
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• Predict what happen after the gametes fertilize if the cell only undergo mitosis
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+ =
2n2n
?
• Predict what happen after the gametes fertilize if the cell only undergo mitosis
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+ =
2n=462n=46
92 chromosomes
Anotomys leander
• The Aquatic Rat, Ecuador Fish-Eating Rat, or Fish-Eating Rat (Anotomys leander) is a species of rodent in the Cricetidae family. It is the only species in the genus Anotomys. It is found only in Ecuador.
• Its natural habitats are subtropical or tropical dry lowland grassland and rivers.
• It has 92 chromosomes
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So, why meiosis important?
• After fertilization of male and female gametes, the offspring will have twice number of chromosomes
• Hence, in order to maintain the same chromosomal number of the offspring, the cell must undergo meiosis.
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Please fill this table in your bioscore book
Organism Chromosomal number
2n n
Cat 38
Monkey 44
Prawn 127
Human 23
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Significance of meiosis
• Meio means reduce
• Meiosis is process of nuclear division that reduces number of chromosome in new cells to the half number of chromosome in parent cells
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• Each gametes receive one chromosomes from every pair of homologous .
• So, gametes contain haploid (n) number of chromosomes
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• Similar with mitosis, meiosis is a continuous process and consist of two separate nuclear division
• Meiosis I• Meiosis II
• However, DNA of each chromosomes replicates once
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• Meiosis I
• Begin with single diploid (2n) parent cell
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• Meiosis II
• End with resulting of four haploid (n) daughter cell
• Each daughter cell genetically distinct from other and also from parent
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• During sexual reproduction, the fusion of two gametes will restore the complete number of chromosome and genetic material
• Diploid zygote will be form.
• The offspring inherit traits from both parent to ensure continuation of life
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• Fertilization of haploid gametes
• = =
• Will produce diploid zygote
• The number of chromosome will maintain for next generation
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Where does meiosis occur?
• Gametes are sex cells (sperm, eggs)
• Arise from germ cells
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testes
ovaries
anther
ovary
Where does meiosis occur
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SpermatogenesisSpermatogenesis
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Answer this question without referring book
• 1. State significance of meiosis
• 2.How many nuclear division do meiosis have? State the division.
• 3.How many daughter cell will produced by meiosis?
• 4. Describe the genetic content of the daughter cells
• 5. Where does meiosis occur (in plant and animal)? What type of cell produce in animal and in plant (state the cell) ?
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Concept correction
• Some organism can have same number of chromosome , however their arrangement of chromosomes are different
• Example: Canis familiaris (domestic dog) 78
Gallus gallus (chicken) 78
Rhesus Monkey 48
Orangutan 48
Deer Mouse 48
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Chromosome• How to count chromosome
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This I single chromosome or chromatid
This I single chromosome or chromatid
The number of chromosome
can count by the number of the
centromere
The number of chromosome
can count by the number of the
centromere
Sister chromatid
centromere
overview
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Interphase IInterphase I
• Similar to mitosismitosis interphase.
• ChromosomesChromosomes replicate (S phase).(S phase).
• Each duplicated chromosomechromosome consist of two identical sister chromatidschromatids attached at their centromerescentromeres.
• CentrioleCentriole pairs also replicate.
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Interphase IInterphase I
• NucleusNucleus and nucleolusnucleolus visible.
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nuclear membrane
nucleolus
cell membrane
chromatin
MEIOSIS I (4 PHASE )
-PROPHASE I-METAPHASE I-ANAPHASE I-TELOPHASE I
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Prophase IProphase I
• Chromosome condense, shorter, thicker and clearly visible
• Homologous chromosomes come together form bivalent through synapsis
• The bivalent visible as four-part structure known as tetrad
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• Tetrad- consist of two homologous chromosome. Each made up of 2 sister chromatids
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Prophase IProphase I - - SynapsisSynapsis
Homologous chromosomes
sister chromatids sister chromatidsTetrad
Homologous Chromosomes
• Pair of chromosomeschromosomes (maternalmaternal and paternalpaternal) that are similar in shape and size.
• Homologous pairs (tetrads) (tetrads) carry genes controlling the same inherited traits.
• Each locuslocus (position of a gene) (position of a gene) is in the same position on homologues.
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Homologous ChromosomesHomologous Chromosomes
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eye color locus
eye color locus
hair color locus
hair color locus
CONTINUE…Prophase I
• Non sister chromatids exchange segments of DNA in crossing over process
• Crossing over resulted new combination of gene on chromosome.
• Chiasmata (chiasma) Chiasmata (chiasma) are the sites of crossing over in which the segment of chromatid change
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Crossing Over - variation Crossing Over - variation
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nonsister chromatids
chiasmata: site of crossing over
variation
Tetrad
Prophase I
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centrioles
spindle fiber
• At the end-nucleolus and nuclear membrane disappear
• Centrioles migrate to opposite poles
• Spindle fiber radiate
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Metaphase IMetaphase I• Tetrad line up at metaphase plate.
• One chromosome of each pair attach to spindle fiber from one pole and its homologoue attach by opposite pole fiber
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Metaphase I
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metaphase plate
OR
metaphase plate
Anaphase IAnaphase I
• Spindle fiber pull the homologous chromosomes to Spindle fiber pull the homologous chromosomes to separate the homologous chromosome s move towards opposite poles.
• Sister chromatids Sister chromatids remain attached at their centromerescentromeres.
• So, although the cell started with 4 chromosomes , only 2 chromosomes move towards each pole
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Anaphase IAnaphase I
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Telophase I
• Chromosomes arrive at poles.
• Each pole now has haploidhaploid set of chromosomes in the chromosomes in the nucleusnucleus
• Spindle fiber disappearSpindle fiber disappear
• Nuclear membrane reappear. Nucleolus reappear in each Nuclear membrane reappear. Nucleolus reappear in each nucleus.nucleus.
• CytokinesisCytokinesis occurs and two haploid daughter cells are formed.
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Telophase ITelophase I
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• Cytokinesis occur simultaneously after telophase I
• Why we need meiosis II?
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MEIOSIS II (4 PHASE )
-PROPHASE II-METAPHASE II-ANAPHASE II-TELOPHASE II
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Meiosis IIMeiosis II
• No interphase II No interphase II
(or very short - no more DNA replicationDNA replication)
-chromosomes remain in condense state
• Remember:Remember: Meiosis II Meiosis II is similar to mitosismitosis
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Prophase IIProphase II
• same as prophase in mitosis
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• Nuclear membrane disintegrate
• Spindle fiber reform
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Metaphase IIMetaphase II
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metaphase platemetaphase plate
• Chromosome-still consist of sister chromatids
• Position randomly at metaphase plate with sister chromatids of each chromosome pointing towaard opposite pole
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Anaphase IIAnaphase II
• sister chromatids separatesister chromatids separate
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• Centromere of sister chromatids separate
• The sister chromatid now is individual chromosomes
• Chromosomes move toward opposite poles
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Telophase IITelophase II
• Nuclear envelope reappear• Nucleoli reform.
• CytokinesisCytokinesis occurs.
• Remember:Remember: four haploid daughter cells four haploid daughter cells produced.produced.
gametes = sperm or egggametes = sperm or egg
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Telophase IITelophase II
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Animation
Meiosis – mouse testes
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Parent cell
4 gametes
1st division
2nd division
Differences of meiosis I and IIMeiosis I Differences Meiosis II
-Homologous chromosome pairs up- crossing over between non sister chromatid
PROPHASE -no synapsis of homologous chromosome- No crossing over
-Homologous chromosomes align at equator
METAPHASE -chromosomes align at equator
-Homologous chromosome separate and move to opposite poles- siser chromatid attach at centromere
ANAPHASE -sister chromatid separate becoming daughter chromosome
-Produce 2 haploid daughter cell-each daughter cell has only one of each type of chromosome
TELOPHASE -4 haploid daughter cell produced-each cell have only one of the sister chromatid-Have same number of chromosome with haploid cell from meiosis I04/07/23Azuwin 2010
Breaktime…
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Differences of mitosis and meiosis
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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.
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• Meiosis I involves:– Synapsis – homologous chromosomes pair up.
Chiasmata form (crossing over of non-sister chromatids).
– In Metaphase I, homologous pairs line up at metaphase plate.
– In Anaphase I, sister chromatids do NOT separate.– Overall, separation of homologous pairs of
chromosomes, rather than sister chromatids of individual chromosome.
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Mitosis vs. meiosis
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Meiosis creates genetic variation
• During normal cell growth, mitosis produces daughter cells identical to parent cell (2n to 2n)
• Meiosis results in genetic variation by shuffling of maternal and paternal chromosomes and crossing over.
• No daughter cells formed during meiosis are genetically identical to either mother or father
• During sexual reproduction, fusion of the unique haploid gametes produces truly unique offspring.
Azuwin 2010
Study Questions1. What happens as homologous chromosomes
pair up during prophase I of meiosis?
2.How does metaphase of mitosis differ from metaphase I of meiosis?
3.What is the sole purpose of meiosis?
4. What specific activities, involving DNA, occur during interphase prior to both mitosis and meiosis?
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5. Compare mitosis and meiosis on the following points:a. number of daughter cells produced.b. the amount of DNA in the daughter cells in contrast to the original cell.
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5.3 Appreciating the movement of chromosomes during mitosis and meiosis
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Meiosis – division error
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Meiosis error - fertilisation
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Should the gamete with the chromosome pair be fertilised then the offspring will not be ‘normal’.
In humans this often occurs with the 21st pair – producing a child with Downs Syndrome
21 trisomy – Downs Syndrome
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Can you see the extra 21st chromosome?
Is this person male or female?
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Monosomy
• refers to lack of one chromosome of the normal complement.
• Monosomy of the sex chromosomes (45,X) causes Turner syndrome.
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trisomy
• Trisomy 18 known as Edwards Syndrome
• Trisomy 13 known as Patau Syndrome
• Trisomy of the sex chromosomes is possible, such as in (47,XXX).
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The end…
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HOW VARIATION OCCUR IN MEIOSIS
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Independent assortment
Number of combinations: 2n
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e.g. 2 chromosomes in haploid2n = 4; n = 22n = 22 = 4 possible combinations
In humans
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e.g. 23 chromosomes in haploid2n = 46; n = 232n = 223 = ~ 8 million possible combinations!
Crossing over
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Chiasmata – sites of crossing over, occur in synapsis. Exchange of genetic material between non-sister chromatids.
Crossing over produces recombinant chromosomes.
Harlequin chromosomes
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Random fertilizationAt least 8 million combinations from Mom,
and another 8 million from Dad …
>64 trillion combinations for a diploid zygote!!!
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Video 3Video 3Video 3Video 3
Video 2Video 2Video 2Video 2Video Video
11Video Video 11
CELL DIVISIONConcept map
Consist of
Occur in
Lead to
CELL DIVISION
Mitosis Meiosis
Controlled mitosisUncontrolled mitosis meiosis I meiosis II
Testis, ovary and anther
Sexual
reproductionSexual
reproduction Non-
disjunctio
n
Non-
disjunctio
n
Cloning (asexual reproduction, regeneration, healing)
Advantages and disadvantages of cloning
cancer
Radioactive and
Carcinogenic
substance
Comprises of
Lead toLead to
considering
Subdivides into
Cause by
www.sumanasinc.com/webcontent
Mah Chee Wai and Dr. Tina Lim Swee Kim (2009).Nexus vista SPM form 4 & 5: Biology. Petaling Jaya:Sasbadi sdn.bhd
www.accessexcellence.org/AB/GG/meiosis.php
Book
Internet sources
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2. Nurul Azuwin bt Yazid UPSI 2010