• 46 Chromosomes
• Trisomy 21 or Monosomy 21
• most common chromosomal disoders *nondisjunction - chromosomes do not split apart
• Robertsonian Translocation - part of two chromosomes switch (chromosome 21 and chromsome 14) Short and long arms
• Mosaic - cells mixed - zygote devices continuous - mitosis - replicate and produce more cells

Physical characteristics: * Heart problems * GI tract *Brain - Alzheimer's * Flat facial profile * Epicanthal fold * Blindness

Major risk factor: maternal age (mother age is 45+)