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Inheritance Patterns. Things that cause alterations in chromosome number or pattern lead to genetic disorders. Alterations in chromosome number - aneuploidy caused by nondisjunction failure of a chromosome to separate during meiosis

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inheritance patterns
Inheritance Patterns
  • Things that cause alterations in chromosome number or pattern lead to genetic disorders.
    • Alterations in chromosome number - aneuploidy
      • caused by nondisjunction
        • failure of a chromosome to separate during meiosis
          • if nondisjunction is of a single chromosome the zygote will either be monosomic or trisomic
          • if nondisjunction is of a entire genome the zygote will exhibit popolyploidy
            • Triploidy, tetraploidy, …
            • Very common in plants but not viable in animals

monosomic

trisomic

examples of syndromes associated with non disjunction
Examples of Syndromes Associated with Non-disjunction
  • monosomic - Turner Syndrome (XO)
    • only viable monosomic disorder in humans
    • 1/500 births
    • sterile, less developed secondary sex characteristics (better with estrogen therapy)
  • trisomic
    • Down Syndrome (trisomy 21)
      • 1/700 births
      • part of the pre-birth screening panel
      • short stature, heart defects, prone to respiratory infections, mental retardation
      • risk increases dramatically for childbearing women over the age of 30
    • XXX
      • Normal outwardly
      • 1/1000 births
    • XXY
      • Klinefelter syndrome
      • under developed genitalia
      • sterile
      • some female sex characteristics - fleshy breasts
      • 1/2000 live births
    • XYY
    • may be taller but otherwise indistinguishable
alteration in chromosome structure
Alteration in Chromosome Structure
  • homologous alterations - often lethal
    • deletion
      • can cause a frame-shift affecting all genes down stream
      • cri du chat syndrome
        • deletion in chromosome 5
        • cry sounds like a mewing cat, microcephaly, retardation, death in early childhood
    • duplication
      • Caused by the attachment of a deleted region during meiosis
      • Causes gene dosing errors
    • inversion
      • Reverse attachment of a deleted region during meiosis
      • Causes reading frame errors in genes
slide4

non-homologous alterations

    • translocation
      • attachment of a deleted region from a non-homologous chromosome
      • reciprocal translocations occur when neighboring chromosomes cross over
        • gene number is conserved although gene dosing secondary to gene position may be affected
      • implicated in many cancers and leukemia
exceptions to mendelian genetics
Exceptions to Mendeliangenetics
  • Genomic imprinting
    • effect of the depends on the sex of the person inherited from
    • occurs during the formation of gametes
    • certain genes are turned off in the sperm & the ova
      • insulin-like growth factor (used in prenatal growth)
        • only the paternal version is expressed
  • Inherited organelle genes (extranuclear genes)
    • circular DNA found in the mitochondria and chloroplasts
    • inherited in the cytoplasm of the ova (maternal)
    • mitochondrial myopathy
      • weakness, intolerance of activity, muscle deterioration