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Ψ Chromosomal Miscount - usually results in spontaneous abortion (miscarriage). An estimated half of all zygotes have an odd number of chromosomes.
Ψ Most zygotes with chromosomal abnormalities are aborted; but, one in 200 are born & in every case have a recognizable syndrome, such as:
• Down syndrome: Trisomy - 21, most common extra-chromosome syndrome
• Klinefelter syndrome (23 location), impairs sexual maturation
• Fragile X syndrome - most common form of inherited mental retardation.
Ψ The variable that most often correlates with chromosomal abnormalities is maternal age.
Ψ Some methods of genetic testing follow:
• PKU or Phenylketonuria (every newborn in the US is tested)
• Alpha-Fetoprotein Assay
• Chorionic villi Sampling (CVS)
• Amniocentesis (reveals sex of the fetus)
• Ultrasound (sonogram)
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Harmful Genes
Dominant disorders:
• Huntington's Chorea - central nervous system disease
• Tourette's Syndrome - tics & twitches, sometimes with uncontrollable speech
• Link to more information on Huntington's Disease. 
Recessive disorders:
• Cystic Fibrosis
• Thalassemia
• Sickle-cell Anemia
Ψ Genes that predispose for schizophrenia occur on chromosomes 1,5,6,10,13,15, & 22.
Ψ Genetic counseling is the process of helping people understand & adapt to the medical, psychological & familial implications of genetic contributions to disease. This process integrates the following:
• Interpretation of family & medical histories to assess the chance of disease occurrence
or recurrence.
• Education about inheritance, testing, management, prevention, resources & research.
• Counseling to promote informed choices and adaptation to the risk or condition.
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