Mistakes in Meiosis

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Mistakes in Meiosis
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Key Terms

• Deletion
• Duplication
• Inversion
• Translocation
• Nondisjunction
• Trisomy
• Monosomy

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Mistakes in Meiosis

• when an error in meiosis occurs, the gamete
  usually does not survive
• on rare occasions when the gamete does survive,
  the zygote will inherit the error
• errors in meiosis usually result in a consequence
  to the offspring

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Mistakes in Meiosis Changes in Chromosome
Structure

• often result from errors in crossing over
• 4 categories of chromosomal errors
• deletions part of a chromosome is missing
• duplications part of a chromosome is repeated
• inversions parts of chromosomes are inverted
  (upside down)
• translocations a part of a chromosome becomes
  attached to a different chromosome

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Mistakes in Meiosis Chromosomal Nondisjunctions

• Nondisjunction when homologous chromosomes do
  not separate correctly in anaphase I (or when
  sister chromatids do not separate correctly in
  anaphase II)
• this results in some gametes having too many
  chromosomes and some gametes having too few
  chromosomes

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Mistakes in Meiosis Chromosomal Nondisjunctions
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Nondisjunction Examples

• Trisomy having one extra chromosome
• Monosomy having one less chromosome
• Down Syndrome trisomy on chromosome 21.
  Characterized by intellectual disabilities and
  almond-shaped eyes
• Turner Syndrome monosomy (XO female has only
  one X chromosome). Characterized by short stature
  sexually underdeveloped