Down Syndrome Causes & Inheritances; Is It Inherited?
      • Most of the time Down Syndrome is not inherited, it's caused by a mistake in cell division during the development of the embryo.
        • Translocation Down Syndrome is the only form of Down Syndrome that can be passed from parent to child.
What Causes Down Syndrome?
      • Happens when chromosome 21 fails to separate during the formation of the egg (or sperm), also known as nondisjunction.
        • Rare cases of Down syndrome is caused by Robertsonian, which occurs when the long arm of chromosome 21 breaks off and attaches to another one at the centromere.
3 Types of Genetic Variations That Cause Down Syndrome:
    1. Trisomy 21
      • Trisomy 21 is when a person has three copies of chromosome 21 instead of two. This is the most common form of Down Syndrome.
    2. Mosaic Down Syndrome
      • Mosaic Down Syndrome is a very rare kind of Down Syndrome. This is cause by abnormal cell division after fertizlization.
    3. Translocation Down Syndrome
      • This form of Down Syndrome is uncommon.
      • People With Translocation Down Syndrome usually have two copies of chromosome 21 but they also have pieces from chromosome 21 to the translocated chromosome.

Signs & Symptoms;
  • Very distinctive facial features such as flat face, small broad nose, abnormally shaped ears, large tongue, and upward slanted eyes with small folds of skin in the corners.
  • Increased risk of developing significant medical problems; respiratory infections, digestion issues, leukemia, heart defects, hearing loss, and various eye abnormalities.
  • Exhibits moderate to severe mental retardation.
  • Life expectancy is usually decreased about half only life to 50 years.
  • Short stature, grows at a slower pace, and is usually abnormally short for an adult.
  • Weak muscles through out the body.
  • Short-wide neck with excessive fat and skin.
  • Short Stocky limbs
  • Small low set ears.
  • Irregularly shaped mouth and tongue.
  • Nose’s bridge is abnormally flat.

Other Information;

  • Down syndrome is really the only trisomy compatible with life. Only two other trisomies have been observed in babies born alive (trisomies 13 and 18), but babies born with these trisomies have only a 5% chance of surviving longer than one year.
  • Most common genetic disorder caused by a chromosomal abnormality. It affects 1 out of every 800 to 1,000 babies.

Works Cited

"Down Syndrome." Learn.Genetics™. N.p., n.d. Web. 3 Mar. 2012. <
"Down Syndrome-Symptoms." WebMD Children's Health Center - Kids health and safety information for a healthy child. N.p., n.d. Web. 3 Mar. 2012.
"Down syndrome: Causes -" Mayo Clinic. N.p., n.d. Web. 3 Mar. 2012.