MITOSIS

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MITOSIS MEIOSIS
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TERMS TO KNOW

• Chromosome contain genetic code/DNA.
• Gene found in chromosomes. They determine an
  individuals characteristics such as eye colour
  nose shape.
• Diploid a cell with the full number of
  chromosomes.
• Haploid cell with half the number of
  chromosomes.

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MITOSIS

• See Atwaroo-Ali for info on chromosome number,
  cell cycle importance of chromosome number.
• One way in which cells divide Mitosis
• Is the process in which one eukaryotic cell
  divides into two cells identical to the parent
  cell
• Mitosis occurs during growth asexual
  reproduction
• Two daughter cells are produced identical to
  parent (i.e. same type of chromosomes)
• Occurs in all body cells divide except sex cells

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MITOSIS

• http//www.sumanasinc.com/webcontent/animations/co
  ntent/mitosis.html
• In order for identical daughter cells to be
  formed the dividing cell must do 2 things
• Must copy each chromosome before it divides.
  Hence, each daughter cell will have a copy of
  each chromosome
• Cell must divide to ensure that each daughter
  cell receives one copy of every chromosome
  otherwise it wont contain all the genes.

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IMPORTANCE OF MITOSIS

• Growth
• Repair
• In asexual reproduction necessary for
  maintenance of species number identical
  combination of genes in daughter cells.

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ASEXUAL REPRODUCTION MITOSIS

• Examples (see Atwaroo-Ali pg 226)
• Binary fission
• Vegetative propagation
• Cuttings
• Grafting
• Tissue culture

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• CLONING
• the processes used to create an exact genetic
  replica of another cell, tissue or organism. The
  copied material, which has the same genetic
  makeup as the original, is referred to as a clone
  

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• Fusion cell cloning
• Fusion cell cloning involves replacing the
  nucleus of an unfertilised egg with the nucleus
  from a different cell. The replacement nucleus
  can come from an embryo, but if it comes from an
  adult cell, it is called adult cell cloning.
• Dolly the sheep was the first mammal to be cloned
  using adult cell cloning. She was born in the UK
  in 1996 and died in 2003. Here's how she was
  produced
• An egg cell was removed from the ovary of an
  adult female sheep, and its nucleus removed.
• The nucleus from an udder cell of a donor sheep
  was inserted into the empty egg cell.
• The fused cell then began to develop normally,
  using genetic information from the donated DNA.
• Before the dividing cells became specialised, the
  embryo was implanted into the uterus of a foster
  mother sheep. The result was Dolly, genetically
  identical to the donor sheep.

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• Learn advantages and disadvantages of cloning
• Do you condone cloning?
• Do you think that humans should be cloned?
  Explain your answer
• What are some concerns with cloning humans?

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GROWTH AND MITOSIS

• Growth increase in of cells. Done via
  mitosis.
• Irreversible increase in mass
• Development increase in complexity, as cells
  differentiate into tissues carry out specific
  functions.

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GROWTH IN ANIMALS

• Growth in animals occurs via the production of
  many cells.
• Continuous process until organism reaches a
  certain size as an adult.
• In some organisms, this increase is not easily
  seen e.g. grasshopper w.r.t. its length. However,
  the increase in mass in a grasshopper is constant.

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• This difference is due to exoskeleton of
  grasshopper. When this skeleton gets too small
  shedded.
• New one is initially soft allowing grasshopper to
  inflate body to stretch it.
• Skeleton hardens at inflated size, leaving room
  for the insect to grow.
• Process is called ecdysis or moulting.

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• Human growth shows gradual increase until
  adulthood.
• However, different parts of body grows at
  different rates at different times.
• Boys girls grow at same rate until teens.
• Girls have an adolescent growth spurt before boys
  reach adult body size at an earlier age.
• Boys are bigger than girls when adults.
• These growths caused by secretion of sex hormones
  which stimulates pituitary gland to secrete
  growth hormone. Growth stops _at_ adulthood.

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GROWTH IN PLANTS

• Growth also involves an increase in cells
• Only cells in certain places (meristems) divide
  via mitosis
• Meristems occur at the ends of shoots roots.
• Thus most plants grow in a branching shape
• See Chinnery and Atwaroo Ali for more info

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• In flowering plants, there is an initial growth
  period after fertilisation
• This results in formation of an embryo within a
  seed germination
• Germination needs the following conditions
• Oxygen - why?
• Water why?
• Suitable temperature why?

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• A seed contains an embryo plant
• Embryo radicle (root) plumule (shoot)
• Food (starch, lipids protein) is stored for the
  embryo in cotyledons. Cotyledon also contains
  enzymes.
• Cotyledons surrounded by testa prevents damage
  to embryo bacteria fungi from entering seed.
• Testa has a tiny hole (micropyle). This hole is
  near to hilum (scar) where seed is joined onto
  the pod (See Chinnery).
• Learn draw seed structure

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• Uptake of water through micropyle initiates
  germination as metabolic reactions begin
• Seed swells, testa bursts, plumule radicle able
  to penetrate testa
• At germination, enzymes digest food into soluble
  substances
• Starch to?
• Proteins to?
• Lipids to?
• What enzymes do the above?
• Plumule grows above ground allowing what?

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TYPES OF GERMINATION

• Hypogeal

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• Epigeal

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• Primary growth
• This occurs when there is growth behind the ends
  of the root shoot and ends of any side branches
  (all regions called apical meristems).
• Mitosis within cells occurs
• New cells elongate to cause growth

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• Secondary growth
• Shoots roots - thicker longer as they grow
• Rings of cells develop in roots shoots

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• Plants and animals grow and differentiate their
  tissues in different ways. The main differences
  are outlined in the table on the next slide.

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Feature Plant Animal
Where growth occurs Mainly at shoot and root tips and in special growth zones like buds New cells can be made by most tissues
How growth occurs Size increase often caused by increasing the size of cells by absorbing water into the vacuole Size increase is brought about by increasing the number of cells
Cell specialisation Most plant cells can differentiate into different cell types Only stem cells can differentiate into different cell types. Other animal cell functions remain fixed
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REFERENCES

• http//www.nlm.nih.gov/medlineplus/cloning.html
• http//bruceleeeowe.wordpress.com/2009/11/07/human
  -cloning-surrogate-mother-and-why-is-it-wrong/
• http//news.bbc.co.uk/2/hi/science/nature/371378.s
  tm
• http//science-education.nih.gov/home2.nsf/Educati
  onalResourcesTopicsGenetics/BC5086E34E4DBA0085256
  CCD006F01CB?OpenDocumentHighlight0,clonedandsh
  eep
• http//videos.howstuffworks.com/hsw/5995-the-impor
  tance-of-meiosis-video.htm
• http//www.vcstulsa.org/Portals/25/Editors/Teacher
  s/mitosis2.ppt256,2,The Importance of Mitosis
• http//www.biology-questions-and-answers.com/cell-
  division.html
• http//www.sci.sdsu.edu/classes/bio100/Lectures/Le
  ct05/lect05.html
• http//www.rapidlearningcenter.com/biology/genetic
  s/04-Mitosis-and-Meiosis.html

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• http//www.bbc.co.uk/schools/gcsebitesize/science/
  edexcel/genes/reproductionandcloningrev4.shtml
• http//www.bbc.co.uk/schools/gcsebitesize/science/
  add_gateway/living/cloningrev4.shtml
• http//www.bbc.co.uk/schools/gcsebitesize/science/
  21c/genetics/cloningstemcellsrev2.shtml
• http//www.bbc.co.uk/schools/gcsebitesize/science/
  add_gateway/living/growinguprev1.shtml
• http//www.bbc.co.uk/schools/gcsebitesize/scien
  ce/aqa/evolution/reproductionrev1.shtml
• Hypogeal Germination http//encyclopedia.farlex.co
  m/_/viewer.aspx?pathhutnamec01094.gif
• Epigeal Germination http//www.uq.edu.au/_School_S
  cience_Lessons/9.112.GIF
• Epigeal http//store.tkc.go.th/multimedia/webprodu
  cer/p01/html/cell2/bodyhtm/image/pic42.gif
• http//www.ornl.gov/sci/techresources/Human_Genome
  /elsi/cloning.shtml
• Secondary growth http//www.biologie.uni-hamburg.d
  e/b-online/library/plant_biology/surecell.html
• http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
  Tilia1_to_3.gif
• http//fig.cox.miami.edu/Faculty/Dana/16002_12.h
  tml
• Primary growth http//www.uic.edu/classes/bios/bio
  s100/lectf03am/lect18.htm

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MEIOSIS

• Most cells of the human body have 46 chromosomes
  (diploid/2n number) in 23 pairs except gametes.
• Each gamete has 23 chromosomes (haploid/n number)
  (23 chromosomes in each egg sperm)
• Only cells in reproductive organs to produce
  gametes
• Meiosis occurs in the ovaries testes of humans
  and anthers ovaries of plants

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• When a human egg cell sperm cell fuse to form a
  zygote, their chromosomes combine to give the
  zygote 46 chromosomes in 23 pairs.
• Zygote continues to divide via mitosis to form
  more cells with 23 pairs of chromosomes each.

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WHY IS MEIOSIS IMPORTANT?

• Meiosis ensures that the haploid number of
  chromosomes is maintained in the gametes so that
  the original number of 46 chromosomes is restored
  when the gametes fuse.
• Allows for genetic variation because crossing
  over brings new gene combinations on chromosomes.
• Process by which gametes are prepared for
  fertilisation.

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PROCESS OF MEIOSIS

• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter3/animation__how_meiosis_works
  .html
• http//highered.mcgraw-hill.com/sites/0072495855/s
  tudent_view0/chapter3/animation__unique_features_o
  f_meiosis.html
• Each chromosome from the mother pairs up with a
  corresponding set from the father. Called
  homologous chromosomes.
• At the start of meiosis, each chromosome divides
  forms 2 identical chromatids joined by one
  centromere.

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• These homologous chromosomes come together
  (called bivalent) causing four chromatids to be
  close.
• Genetic information is now able to pass from one
  chromosome to the next. This is called crossing
  over.
• In metaphase I, the homologous chromosomes align
  randomly on the equator, then separate, then move
  to opposite ends of the cell to allow for cell to
  split into 2.

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• Again the chromosomes align along the equator of
  the cell but this time the chromatids separate
  4 daughter cells have genetic info from
  original chromosomes

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SEX DETERMINATION

• Gender is determined by chromosomes
• Sex chromosomes X or Y chromosomes, named based
  on shape of chromosomes
• Females have 2X chromosomes, males have an XY
  pair
• However, only one chromosome will be present in
  the gamete

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• Gametes fuse during fertilisation to form a
  zygote with 2 sex chromosomes.
• The combination of XY determines the sex of the
  baby.
• One X one Y ?
• Two X chromosomes ?

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• See pages 236 237 of Atwaroo-Ali

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• http//activity.ntsec.gov.tw/lifeworld/english/con
  tent/gene_cc5.html
• http//www.biology4kids.com/files/cell_chromosome.
  html
• http//highered.mcgraw-hill.com/sites/007249585
  5/student_view0/chapter3/animation__how_meiosis_wo
  rks.html
• http//www.sumanasinc.com/webcontent/animations/
  content/meiosis.html
• http//www.biologycorner.com/bio1/celldivision-chr
  omosomes.html