KARYOTYPING AND NON-DISJUNCTION

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KARYOTYPING AND NON-DISJUNCTION
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What is karyotyping?

• A method of identification of chromosomes
• Pictures of chromosomes are taken as the cell
  undergoes mitosis
• The image is enlarged
• Individual chromosomes are cut up
• Chromosomes are matched up based on
• Size (largest to smallest)
• Centromere position
• G-banding

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A mess of chromosomes
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After karyotyping a normal male
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After karyotypingnormal
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Non-disjunctionnondisjunction

• 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)
• All but one monosomy case results in death

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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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Downs Syndrome

• Most commonly known trisonomy
• 1700 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

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Downs syndrome
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Downs Syndrome

• One of the most common causes of mental
  disability (IQ is in the 25-75 range)
• Prone to heart defects, respiratory problems and
  leukemia

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Downs Syndrome

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

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Patau Syndrome

• 115,000 births as most fetuses die before term
• Of those that survive, 5 live to age 3 45 die
  within the first month
• Serious eye, brain, and circulatory defects

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Pataus Syndrome
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Edwards Syndrome

• Only 10 survive past one year
• All die early in infancy
• Many complications

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• These are the only known trisonomy genetic
  disorders that result in offspring surviving for
  a short period of time

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Non-disjunction of the sex chromosomes

• These can be fatal
• Most do survive just fine

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Klinefelters Syndrome

• Affects 1500 males
• XXY
• Tall, sterile males
• Normal intelligence
• Has female characteristics

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Klinefelters Syndrome
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Jacobs Syndrome (super male)

• XYY
• Somewhat taller than average
• Slightly below normal intelligence
• 11000 males
• Extra testosterone

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XXX (super female?)

• 11000 live births
• Normal intelligence
• Fertile
• No physical problems
• There are some women who are XXXX and XXXXX
  each increasing X results in lesser intelligence
  and fertility

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Monosomy Turners Syndrome (XO)

• 12700 births
• Live normal lives but do not mature sexually at
  puberty
• Sterile
• Short stature
• Short broad neck
• Broad chest

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Other chromosomal issues

• Deletion a segment of the chromosome is missing
• Example Cri-du-chat (11,000,000)
• Improperly developed larynx
• Severely mentally handicapped

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Other chromosomal issues

• Duplication
• Ex. Fragile X
• 11500 males, 2500 females
• Most common form of mentally handicapped
  offspring

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