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Genetic Disorders

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Recessive Disorders

  • Phenylketonuria (PKU)
    • Cause
      • Homozygous recessive genotype for PKU alleles

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    • Effects
      • Lack enzyme to convert the amino acid phenylanine to tyrosine
      • Phenylanine accumulates in blood and harms nervous system
      • Causes profound mental retardation
      • Symptoms appear a couple of months after birth
      • Those effected have regular convulsions and seizures and must be hospitalized for lifespan which lasts about 30 years

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Recessive Disorders

  • Albinism
    • Cause
      • homozygous inherited autosomal recessives
    • Effects
      • lack the enzyme to produce melanin
      • or enzyme that produces melanin is not functional

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Recessive Disorder

  • Tay-Sachs Disease
    • Cause
      • homozygous inherited autosomal recessives
    • Effects (CORRECTION TO NOTES!)
      • Lack enzyme to break down fatty acids
      • Fatty acids accumulate in the brain and effect central nervous system

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Recessive Disorder

  • Sickle – Cell Anemia
    • Cause
      • homozygous inherited autosomal recessives
    • Effects
      • single amino acid substitution in hemoglobin
      • oxygen concentration becomes low and hemoglobin forms stiff fibers
      • causes red blood cells to have distorted (sickle) shape and become fragile
      • leads to premature degradation of red blood cells
      • lack of flexibility causes blood cells to have difficulty passing through small blood vessels
      • Causes blockage of blood vessels and vital organs

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Sickle – Cell Anemia

normal red

blood cell

sickle cell

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Dominant Disorders

  • Dwarfism
    • Cause
      • Inherited dominant allele
    • Effects
      • Stunted growth throughout lifespan

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Dominant Disorder

  • Huntington’s
    • Cause
      • Inherited dominant allele
    • Effects
      • Mental retardation onset after the age of 30

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Effect of HD on the Basal Ganglia

Normal Basal Ganglia

HD Basal Ganglia

vs.

The basal ganglia of the human brain, showing the impact of HD on brain structure in this region. Note especially that the brain of a person with HD has bigger openings due to the death of nerve cells in that region.

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Sex-Linked Disorder

  • Hemophilia
    • Cause
      • Inherited recessive allele on the X chromosome
      • Male to male inheritance is impossible

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    • Effects
    • Blood is not able to clot normally
    • Minor cuts could possibly lead to

bleeding to death

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Sex-Linked Disorder

  • Muscular Dystrophy
    • Cause
      • Inherited recessive allele on X chromosome
      • Male to male inheritance is impossible

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    • Effects
      • Causes wasting away of muscles
      • Symptoms usually occur beginning at ages 2-6

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Ethnic Variance

  • PKU
    • More frequent in Asians and Caucasians
  • Tay-Sachs
    • More commonly found in Jewish bloodlines
  • Sickle-Cell
    • More prevalent among African-Americans