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KARYOTYPING AND NON-DISJUNCTION

KARYOTYPING AND NON-DISJUNCTION. Please take out your Gizmo worksheet and vocabulary sheet. Learning Goals. Understand what a karyotype is and how to analyze it Learn about symptoms of various syndromes

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KARYOTYPING AND NON-DISJUNCTION

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  1. KARYOTYPING AND NON-DISJUNCTION Please take out your Gizmo worksheet and vocabulary sheet

  2. Learning Goals • Understand what a karyotype is and how to analyze it • Learn about symptoms of various syndromes • Understand the process of nondisjunction and how it explains the genetic basis of various syndromes

  3. Agenda for Today • Take up Gizmo • Lesson on Karyotyping • Playdough activity • Lesson on nondisjuction • Nondisjunction worksheet • Reading on Gregor Mendel

  4. What is karyotyping? • A picture of a cell’s complete set of chromosomes grouped together in pairs and arranged in order of decreasing size • Pictures of chromosomes are taken as the cell undergoes mitosis (metaphase)

  5. Types of Chromosomes • Sex Chromosomes • One of two chromsomes that determine an individuals sex • In humans and most mammals the two sex chromosomes are the X and Y • Females: XX Males: XY • Autosomal Chromosomes • A chromosome that is not a sex chromosome • Humans have 22 pairs of autosomal chromosomes

  6. How do the X and Y Chromosomes Compare? • X is larger than Y • X chromosome contains about 1,000 functioning genes while the Y chromosome only has about 80 WHY??

  7. How do the X and Y Chromosomes Compare? They Y chromosome is only carried by approximately 50% of the population. Therefore, it cannot carry genes that are necessary for an individual's survival. The genes on the Y chromosome code for only male-specific traits

  8. Preparing A Karyotype • Harvested cells are first cultured • The cells are then treated with colchicine which arrests the cells in metaphase, and then treated and stained to observe the chromosomes • Chromosomes can be photographed or visualized using a computer, and then analyzed • Chromosomes are identified by size, position of the centromere, and banding and staining regions

  9. Preparing A Karyotype

  10. A mess of chromosomes…

  11. Analysis of a Karyotype • The analysis involves comparing chromosomes for their: • Length • Placement of centromeres (areas where the two chromatids are joined) • Banding pattern.

  12. male After karyotyping… a normal

  13. female After karyotyping… a normal

  14. What is wrong with this picture?

  15. Down’s syndrome

  16. Down’s Syndrome • Most commonly known trisonomy 21 • 1:700 births; 1 in 6 die within 1st year • Average age is 16.2 years • Common facial feature • Short stature • Stubby fingers and toes • Large tongue – makes speech difficult

  17. Down’s Syndrome • Odds of having a Down’s child increases with the age of the mother • 1 in 1500 if mom is in early 20’s • 1 in 70 if mom is over 35 • 1 in 25 if mom is over 45

  18. What is wrong with this picture?

  19. Edward’s Syndrome • Only 10% survive past one year • All die early in infancy • Many complications

  20. What is wrong with this picture?

  21. Klinefelter’s Syndrome • Affects 1:500 males • XXY • Tall, sterile males • Normal intelligence • Has female characteristics

  22. Klinefelter’s Syndrome

  23. What is wrong with this picture?

  24. Monosomy – Turner’s Syndrome (XO) • 1:2700 births • Live normal lives but do not mature sexually at puberty • Sterile • Short stature • Short broad neck • Broad chest

  25. Jacob’s Syndrome (super male) • XYY • Somewhat taller than average • Slightly below normal intelligence • 1:1000 males • Extra testosterone

  26. XXX (super female?) • 1:1000 live births • Normal intelligence • Fertile • No physical problems • What is the sex of this person?

  27. How Do These Disorders Occur? You have 10 minutes to complete the following activity. Working in your table groups: • Obtain a handful of 2 colours of playdough (do not mix them) • Build 2 different coloured homologous, replicated chromosomes • Using your chromosomes simulate meiosis • Where does meiosis need to go wrong in order to end up with a monosomic or trisomic disorder. There are two possibilities.

  28. Non-disjunction • Non-disjunction is a failure of chromosomes to properly separate during either Stage 1 or Stage 2 of meiosis • Upon fertilization the zygote may have one too many chromosomes ( trisomy) or one too few chromosomes (monosomy)

  29. Non-disjunction • Non-disjunction occurs quite often among humans • Impact is so severe to the zygote that miscarriage occurs very early in the pregnancy • If the baby survives, it develops a set of traits that we call a syndrome

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