Ch. 15

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Ch. 15
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X Inactivation

• Females inherit two x chromosomes, but one in
  each cell becomes inactivated
• The inactivated X condenses into a Barr body
• Which X chromosome is inactivated in each cell is
  randomfemales are a mosaic of two types of cells

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Barr bodies

• The gene for fur color in cats is on the X
  chromosome
• Different colors are expressed, based on which X
  is activecool

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Diseases from Chromosomal abnormalities

• Non disjunction Trisomy or Monosomy

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Human disorders

• Trisomy 13 Down Syndrome
• Monosomy X Turners syndrome
• XXY Klinefelters syndrome

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Structural Alterations

• Other mistakes in Meiosis can lead to breakage in
  the chromosomes and

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Human Disorders

• Chronic mylegenous leukemia (CML)exchange of
  chromosome 9 and 13
• Cri du chatchromosome 5

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Unusual inheritance patterns

• Genomic imprinting silencing of one allele of
  certain genes
• Imprints are transmitted at fertilization, so a
  silenced gene remains silenced in all cells
• Each imprinted the same way, silencing either
  male or female

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Unusual inheritance patterns

• Inheritance of organelle genes mitochondria and
  chloroplasts contain a small circular DNA (like
  bacteria! Hmmm)
• These are usually only inherited from
  Mommaternally
• The egg is bigger and provides your first
  cytoplasm and organelles!