Chromosome Genetics

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Chromosome Genetics

• 1. Karyotypes
• 2. Nondisjunction
• 3. Chromosome mutations

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Karyotypes

• 1. Cell sample fixed, stained, spread on
  microscope slide
• 2. Slide examined, chromosomes located,
  photographed
• 3. Chromosomes arranged in pairs by size,
  centromere location, banding pattern
• 4. Longest to shortest, sex chromosomes separate

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Nondisjunction

• 1. Occurs during Anaphase I or II
• 2. Homologous pair fail to separate
• 3. One gamete receives both homologous
  chromosomes one is missing chromosome
• 4. Trisomy, monosomy

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Nondisjunction Syndromes

• 1. Most trisomy monosomy are lethal
• 2. Automal- Trisomy 21 (Down), Trisomy 18
  (Edward), Trisomy 13 (Patau)
• 3. Sex chromosomes- XO (Turner), XXX or XXXX
  (super female), XXY or XXXY (Klinefelter), XYY
  (Jacobs)

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Jacob Color blindness

• A Jacob syndrome individual is color blind. Both
  his parents have normal vision, but his maternal
  uncle is color blind. In which parent at what
  meiotic division did nondisjunction occur?

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Jacob Color blindness

• a. Identify dominant recessive traits and
  assign symbols

Let B normal vison b color blind
vision X female chromosome Y
male chromosome
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If nondisjunction was mom

• b.

P XBXb x XBY
c.
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If nondisjunction was dad Meiosis I

• b.

P XBXb x XBY
c.
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If nondisjunction was dad Meiosis II

• b.

P XBXb x XBY
c.
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Jacob Color blindness

• d. Answer the question

A nondisjunction event occurred in the
individuals father during Meiosis II
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Chromosomal Mutations

• 1. Inversion
• 2. Translocation
• 3. Deletion
• 4. Duplication

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Inversion

• 1. Chromosome segment breaks apart
• 2. Rejoins in reversed direction, turned 180o
• 3. Same genes present, but sequence of genes is
  reversed

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Translocation

• 1. Movement of segment from one chromosome to
  another nonhomologous chromosomes
• 2. 5 of Down syndrome result of translocation
  between chromosomes 21 and 14

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Deletion

• 1. End of chromosome or ends of chromosome pair
  break off
• 2. Cri du chat- portion of chromosome 5 deleted

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Duplication

• 1. Mispairing- unequal cross-over results in
  chromosome segment repeats
• 2. Common in human cells, multiple copies for
  hemoglobin

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