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Meiosis (Core)

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For the IB Biology course. If you want the editable pptx file, please make a donation to one of my chosen charities. More information here: http://sciencevideos.wordpress.com/about/biology4good/

For the IB Biology course. If you want the editable pptx file, please make a donation to one of my chosen charities. More information here: http://sciencevideos.wordpress.com/about/biology4good/

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  • 1. Meiosis (Core)
    Stephen Taylor
    4.2 Meiosis (Core)
    1
    http://sciencevideos.wordpress.com
  • 2. Meiosis
    A reduction division of nuclei to form haploid gametes.
    4.2 Meiosis (Core)
    2
    http://sciencevideos.wordpress.com
  • 3. Meiosis
    A reduction division of nuclei to form haploid gametes.
    Somatic cell nuclei (body cells) are diploid (2n).
    They contain an homologous pair of each chromosome. Humans have 23 pairs of chromomes(n=23).
    A diploid (2n) cell therefore contains 2x23 = 46 chromosomes.
    In this example cell we see two pairs of homologous chromosomes.
    It is a diploid cell of n=2.
    4.2 Meiosis (Core)
    3
    http://sciencevideos.wordpress.com
  • 4. Meiosis
    A reduction division of nuclei to form haploid gametes.
    Somatic cell nuclei (body cells) are diploid (2n).
    They contain an homologous pair of each chromosome. Humans have 23 pairs of chromomes(n=23).
    A diploid (2n) cell therefore contains 2x23 = 46 chromosomes.
    These chromosomes replicate in the S-phase of interphase to make pairs of sister chromatids, joined at the centromere.
    Each chromosome has replicated.
    It is still diploid but now they are know as pairs of sister chromatids.
    4.2 Meiosis (Core)
    4
    http://sciencevideos.wordpress.com
  • 5. Meiosis
    A reduction division of nuclei to form haploid gametes.
    Somatic cell nuclei (body cells) are diploid (2n).
    They contain an homologous pair of each chromosome. Humans have 23 pairs of chromomes(n=23).
    A diploid (2n) cell therefore contains 2x23 = 46 chromosomes.
    These chromosomes replicate in the S-phase of interphase to make pairs of sister chromatids, joined at the centromere.
    Meiosis is a process of two divisions.
    Meiosis I separates the homologous pairs – this is the reduction division.
    The homologous pairs have separated but the sister chromatids remain attached.
    4.2 Meiosis (Core)
    5
    http://sciencevideos.wordpress.com
  • 6. Meiosis
    A reduction division of nuclei to form haploid gametes.
    Somatic cell nuclei (body cells) are diploid (2n).
    They contain an homologous pair of each chromosome. Humans have 23 pairs of chromomes(n=23).
    A diploid (2n) cell therefore contains 2x23 = 46 chromosomes.
    These chromosomes replicate in the S-phase of interphase to make pairs of sister chromatids, joined at the centromere.
    Meiosis is a process of two divisions.
    Meiosis I separates the homologous pairs – this is the reduction division.
    Meiosis II separates the sister chromatids.
    The end product of meiosis from a single somatic diploid cell is four haploid gametes.
    4.2 Meiosis (Core)
    6
    http://sciencevideos.wordpress.com
  • 7. Homologous Chromosomes
    same structure
    Somatic cell nuclei (body cells) are diploid (2n).
    They contain an homologous pair of each chromosome.
    One of the pair is paternal – inherited from the father.
    The other is maternal – inherited from the mother.
    Homologous chromosomes are the same size and structure. They carry the same genes at the same loci.
    Alleles carried at each locus may vary.
    22 of the human chromosome pairs are homologous. The other pair, the sex chromosomes, are non-homologous.
    Banding pattern
    Centromere position
    size
    4.2 Meiosis (Core)
    7
    http://sciencevideos.wordpress.com
  • 8. Interphase
    In preparation for the reduction division of meiosis, the chromosomes replicate.
    This occurs in the Synthesis phase (S-phase) of meiosis, through DNA Replication.
    Each single chromosome becomes a pair of sister chromatids, physically joined at the equator.
    The centromere is a junction between the sister chromatids.
    4.2 Meiosis (Core)
    8
    http://sciencevideos.wordpress.com
  • 9. Prophase I
    The homologous chromosomes associate with each other.
    The nuclear membrane breaks down and centrioles migrate to the poles.
    4.2 Meiosis (Core)
    9
    http://sciencevideos.wordpress.com
  • 10. Prophase I
    The homologous chromosomes associate with each other.
    Crossing-over between non-sister chromatids can take place.
    The nuclear membrane breaks down and centrioles migrate to the poles.
    This results in recombination of alleles and is a source of genetic variation in gametes.
    4.2 Meiosis (Core)
    10
    http://sciencevideos.wordpress.com
  • 11. Metaphase I
    The bivalents (homologous pairs) line up at the equator.
    Random orientation of these homologous pairs (the way they face) leads to massive genetic variation in the gametes.
    There are 223 possible orientations in humans – well over 8 million!
    4.2 Meiosis (Core)
    11
    http://sciencevideos.wordpress.com
  • 12. Anaphase I
    Spindle fibres contract.
    Homologous pairs are separated and pulled to opposing poles.
    This is the reduction division.
    Non-disjunction here will affect the chromosome number of all four gametes.
    4.2 Meiosis (Core)
    12
    http://sciencevideos.wordpress.com
  • 13. Telophase I
    New nuclei form and the cytoplasm begins to divide by cytokinesis.
    The nuclei are no longer diploid.
    They each contain one pair of sister chromatids for each of the species’ chromosomes.
    If crossing-over and recombination has occurred then the sister chromatids will not be exact copies.
    4.2 Meiosis (Core)
    13
    http://sciencevideos.wordpress.com
  • 14. Interphase
    There is no Synthesis phase in Interphase II.
    4.2 Meiosis (Core)
    14
    http://sciencevideos.wordpress.com
  • 15. Prophase II
    The nuclei break down.
    No crossing-over occurs.
    4.2 Meiosis (Core)
    15
    http://sciencevideos.wordpress.com
  • 16. Metaphase II
    Pairs of sister chromatids align at the equator. Spindle fibres form and attach at the centromeres.
    Random orientation again contributes to variation in the gametes, though not to such an extent as in metaphase I.
    This is because there is only a difference between chromatids where crossing-over has taken place.
    4.2 Meiosis (Core)
    16
    http://sciencevideos.wordpress.com
  • 17. Anaphase II
    Spindle fibres contract and the centromeres are broken.
    The pairs of sister chromatids are pulled to opposing poles.
    Non-disjunction here will lead to two gametes containing the wrong chromosome number.
    4.2 Meiosis (Core)
    17
    http://sciencevideos.wordpress.com
  • 18. Telophase II
    New haploid nuclei are formed.
    Cytokinesis begins, splitting the cells.
    The end result of meiosis is four haploid gamete cells.
    Fertilisation of these haploid gametes will produce a diploid zygote.
    4.2 Meiosis (Core)
    18
    http://sciencevideos.wordpress.com
  • 19. Outline the Process of Meiosis
    4.2 Meiosis (Core)
    19
    http://sciencevideos.wordpress.com
  • 20. Outline the Process of Meiosis
    4.2 Meiosis (Core)
    20
    http://sciencevideos.wordpress.com
  • 21. Outline the Process of Meiosis
    4.2 Meiosis (Core)
    21
    http://sciencevideos.wordpress.com
  • 22. Non-disjunction
    Normal meiosis produces
    four haploid gametes.
    Meiosis I
    Reduction division
    4.2 Meiosis (Core)
    22
    http://sciencevideos.wordpress.com
  • 23. Non-disjunction
    Normal meiosis produces
    four haploid gametes.
    Meiosis I
    Reduction division
    Meiosis II
    Meiosis II
    Separation of sister chromatids
    n
    n
    n
    n
    4.2 Meiosis (Core)
    23
    http://sciencevideos.wordpress.com
  • 24. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    4.2 Meiosis (Core)
    24
    http://sciencevideos.wordpress.com
  • 25. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    Meiosis I
    Reduction division
    4.2 Meiosis (Core)
    25
    http://sciencevideos.wordpress.com
  • 26. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    Meiosis I
    Reduction division
    4.2 Meiosis (Core)
    26
    http://sciencevideos.wordpress.com
  • 27. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    Meiosis I
    Reduction division
    Meiosis II
    Meiosis II
    Separation of sister chromatids
    n-1
    n-1
    n+1
    n+1
    4.2 Meiosis (Core)
    27
    http://sciencevideos.wordpress.com
  • 28. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    Meiosis I
    Reduction division
    4.2 Meiosis (Core)
    28
    http://sciencevideos.wordpress.com
  • 29. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    Meiosis I
    Reduction division
    4.2 Meiosis (Core)
    29
    http://sciencevideos.wordpress.com
  • 30. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction can occur anaphase I or anaphase II.
    In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole.
    Meiosis I
    Reduction division
    Meiosis II
    Meiosis II
    Separation of sister chromatids
    n+1
    n
    n
    n-1
    4.2 Meiosis (Core)
    30
    http://sciencevideos.wordpress.com
  • 31. Non-disjunction
    Non-disjunction leads to changes in chromosome number.
    Non-disjunction in Meiosis II
    Non-disjunction in Meiosis I
    Animation from BioStudio:
    http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20II.htm
    Animation from BioStudio:
    http://www.biostudio.com/d_%20Meiotic%20Nondisjunction%20Meiosis%20I.htm
    Half of gametes affected.
    All gametes affected.
    4.2 Meiosis (Core)
    31
    http://sciencevideos.wordpress.com
  • 32. Non-disjunction & Trisomy Disorders
    Non-disjunction produces gametes with an abnormal number of chromosomes.
    Fertilisation adds the homologous chromosomes…
    n
    n+1
    4.2 Meiosis (Core)
    32
    http://sciencevideos.wordpress.com
  • 33. Non-disjunction & Trisomy Disorders
    Non-disjunction produces gametes with an abnormal number of chromosomes.
    Fertilisation adds the homologous chromosomes…
    n
    n+1
    Resulting in a zygote and somatic cells with a trisomy of one chromosome. This can be fatal or cause disorders.
    4.2 Meiosis (Core)
    33
    http://sciencevideos.wordpress.com
  • 34. Down Syndrome
    Trisomy 21
    Non-disjunction in anaphase I or II
    leads to an extra copy of chromosome 21 in the gamete (usually the egg).
    Fertilisation by a sperm adds the homologous chromosome 21, leading to trisomy.
    Down Syndrome has very distinctive physical characteristics and patients have a slightly shortened life expectancy, learning difficulties and a generally happy nature.
    Computer-enhanced karyogram (adapted):
    http://www.smd.lt/bureliu_upload/genetika/karyogram.gif
    NSW Down Syndrome Video:
    http://www.youtube.com/watch?v=tDjnNDRP_2o
    4.2 Meiosis (Core)
    34
    http://sciencevideos.wordpress.com
  • 35. Maternal Age and Down Syndrome
    Risk of Down Syndrome is strongly correlated with maternal age.
    Use this graph to generate your own data analysis questions.
    http://ibis.health.utah.gov/indicator/view/BrthDefDownSyn.BrthPrevAge.html
    4.2 Meiosis (Core)
    35
    http://sciencevideos.wordpress.com
  • 36. Maternal Age and Down Syndrome
    Girls are born with the precursors to all the eggs they’ll ever need in their ovaries. Beginning with puberty, these eggs start to mature and go through meiosis. This continues until menopause.
    Mother’s age is a high risk factor in Down Syndrome. Think about how long those eggs might have been there! However, many cases of Down Syndrome are with younger mothers.
    Generally women over the age of 40 are advised to have a karyotype of their fetus analysed. This can give the woman information she needs to decide whether to continue the pregnancy and if she decides to continue, how to prepare.
    There is some risk to the pregnancy of carrying out the tests. This is outlined on the chorionic villus sampling or amniocentesis page.
    Risk of Down Syndrome is strongly correlated with maternal age.
    Use this graph to generate your own data analysis questions.
    http://ibis.health.utah.gov/indicator/view/BrthDefDownSyn.BrthPrevAge.html
    Ethics and Discussions:
    • What are the laws about termination of a pregnancy where you are?
    • 37. What are the ethical issues regarding pre-natal testing and abortion?
    • 38. “Forewarned is forearmed,” Discuss.
    4.2 Meiosis (Core)
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    http://sciencevideos.wordpress.com
  • 39. Karyotyping
    Pre-natal test used to check for gender and trisomy disorders.
    Extract fetal cells by amniocentesis or chorionic villus sampling.
    Culture cells and stimulate mitosis.
    Stop division in metaphase.
    Banding pattern
    Take a photograph under the light
    microscope or scan with a computer.
    Arrange chromosomes in homologous pairs based on size, banding patterns and centromere positions.
    6. Check for gender (XX or XY) or trisomy disorders.
    Centromere position
    size
    Karyotype animation:
    http://learn.genetics.utah.edu/content/begin/traits/karyotype/
    Step-by-step animation:
    http://www.mwit.ac.th/~bio/assets/karyotype_mutation.swf
    4.2 Meiosis (Core)
    37
    http://sciencevideos.wordpress.com
  • 40. Chorionic Villus Sampling or Amniocentesis?
    Amniocentesis animation from:
    http://www.medindia.net/animation/amniocentesis.asp
    Chorionic villus sampling animation from:
    http://video.about.com/pregnancy/Chorionic-Villus-Sampling.htm
    Amniocentesis:
    • After 15 weeks
    • 41. Via abdomen
    • 42. Risk of miscarriage: around 1 in 1,000
    Chorionic Villus Sampling:
    • 10-12 weeks
    • 43. Via cervix or abdomen
    • 44. Risk of miscarriage: up to 1 in 100
    Find out more: what are the differences between 12-week and 15-week fetuses and how might this affect the mother’s decision making?
    4.2 Meiosis (Core)
    38
    http://sciencevideos.wordpress.com
  • 45. Nuchal Translucency Scans
    Non-syllabus
    Amniocentesis and CVS cell extraction run a risk of miscarriage.
    The non-invasive nuchal translucency scan allows doctors to determine whether there is need for a karyotype.
    If the nuchal fold is large and fluid-filled, it can be an indicator of Down Syndrome. If it is normal, Down Syndrome is very unlikely.
    Nuchal translucency scan – is it positive or negative?
    http://www.youtube.com/watch?v=Jt3cX2vuMyM
    Find out more about Down Syndrome and screening from the UK’s NHS: http://www.nhs.uk/news/2008/11November/Pages/DownssyndromeQA.aspx
    Can you see the difference between these two scans? What advice would the doctor give?
    http://www.babycentre.co.uk/pregnancy/antenatalhealth/scans/nuchalscan/
    4.2 Meiosis (Core)
    39
    http://sciencevideos.wordpress.com
  • 46. Explain how inheritance of chromosome 21 can lead to Down Syndrome.
    3 marks
    4.2 Meiosis (Core)
    40
    http://sciencevideos.wordpress.com
  • 47. Explain how inheritance of chromosome 21 can lead to Down Syndrome.
    3 marks
    “…inheritance of chromosome 21”
    • Eggs are produced through meiosis. Non-disjunction can occur.
    • 48. This is when a homologous pair of chromosome 21 fail to separate (anaphase I) or a pair of sister 21 chromatids fail to separate (anaphase II).
    • 49. It can occur in anaphase I or II.
    • 50. The resulting gamete will contain two copies of chromosome 21 instead of one.
    “…lead to Down Syndrome”
    • Fertilisation leads to a trisomy of chromosome 21 (causing Down Syndrome in the child).
    4.2 Meiosis (Core)
    41
    http://sciencevideos.wordpress.com
  • 51. Analyse this Karyotype
    Gender:
    Trisomy:
    Computer-enhanced karyogram:
    http://www.smd.lt/bureliu_upload/genetika/karyogram.gif
    4.2 Meiosis (Core)
    42
    http://sciencevideos.wordpress.com
  • 52. Analyse this Karyotype
    Gender:
    • Male
    Trisomy:
    • 13
    Computer-enhanced karyogram:
    http://www.smd.lt/bureliu_upload/genetika/karyogram.gif
    4.2 Meiosis (Core)
    43
    http://sciencevideos.wordpress.com
  • 53. Analyse this Karyotype
    Gender:
    Trisomy:
    Karyogram from Tokyo Medical University:
    http://www.tokyo-med.ac.jp/genet/cki-e.htm
    4.2 Meiosis (Core)
    44
    http://sciencevideos.wordpress.com
  • 54. Analyse this Karyotype
    Gender:
    • Female
    Trisomy:
    Karyogram from Tokyo Medical University:
    http://www.tokyo-med.ac.jp/genet/cki-e.htm
    4.2 Meiosis (Core)
    45
    http://sciencevideos.wordpress.com
  • 56. Analyse this Karyotype
    Gender:
    Trisomy:
    Karyogram from Tokyo Medical University:
    http://www.tokyo-med.ac.jp/genet/cki-e.htm
    4.2 Meiosis (Core)
    46
    http://sciencevideos.wordpress.com
  • 57. Analyse this Karyotype
    Gender:
    • Male
    Trisomy:
    Karyogram from Tokyo Medical University:
    http://www.tokyo-med.ac.jp/genet/cki-e.htm
    4.2 Meiosis (Core)
    47
    http://sciencevideos.wordpress.com
  • 59. Analyse this Karyotype
    Gender:
    Trisomy:
    Karyogram from Tokyo Medical University:
    http://www.tokyo-med.ac.jp/genet/cki-e.htm
    4.2 Meiosis (Core)
    48
    http://sciencevideos.wordpress.com
  • 60. Analyse this Karyotype
    Gender:
    • Female
    Trisomy:
    • Monosomy X
    Turner Syndrome
    Karyogram from Tokyo Medical University:
    http://www.tokyo-med.ac.jp/genet/cki-e.htm
    Remember- if some gametes have an extra chromosome (n+1) due to non-disjunction, then others must be missing a chromosome (n-1).
    4.2 Meiosis (Core)
    49
    http://sciencevideos.wordpress.com
  • 61. For more IB Biology resources:
    http://sciencevideos.wordpress.com
    This presentation is free to view. Please make a donation to one of my chosen charities at Gifts4Good and I will send you the editable pptx file.
    Click here for more information about Biology4Good charity donations.
    4.2 Meiosis (Core)
    50
    This is a Creative Commons presentation. It may be linked and embedded but not sold or re-hosted.