GENETIC DISORDERS

3. Additional chromosomes

In some cases entire chromosomes, or large segments of them, are missing, duplicated, or otherwise altered. Down Syndrome and Turner's Syndrome are examples of this type of disorder. The extra chromosome creates differences that make people recognizable by physical traits in common.

One type of Down Syndrome results when three, rather than the normal two, copies of chromosome 21 are present in each cell (trisomy 21).

An unusual number of chromosomes results when a mistake called nondisjunction occurs in the production of eggs or sperm. Whereas in most cases three copies of a chromosome are lethal to the embryo, in certain cases an extra or missing chromosome is tolerated.

Individuals with an extra chromosome often have serious medical problems due to the imbalance in gene products expressed from that chromosome.

Sandra Jensen had to fight doctors' prejudices to become eligible for a heart transplant. MORE

In the case of Down Syndrome, trisomy 21 may cause any of a series of potential developmental delays, characteristic facial features, and decreased muscle tone, resulting in wide range of intellectual and physical abilities.

Although it is a common disability, as a society we have a lack of awareness about it. People with Down Syndrome face discrimination based on the way the look and misunderstandings about their disorder. (Genetic Science Learning Center, University of Utah).

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