Part one of term paper
The chromosomal abnormality involved in most cases of Down syndrome is trisomy-21, or the presence of three copies of the 21st chromosome. As a result, the affected person has 47 chromosomes in all body cells instead of the normal 46, although how this causes the condition's symptoms is not yet known. Scientists assume that the reason for th ...

Part two of term paper
... into the same sperm or ovum instead of separating. In the type of Down syndrome called translocation, the extra chromosome 21 material is attached to one of the other chromosomes; when some, but not all, of the body's cells carry an extra chromosome 21, the condition is a type of Down syndrome called mosaicism. Because of the extra chromosome 21, children with Down syndrome often have some characteristic physical features, such as a small head, a flat face, slightly upward slanted eyelids, skin fo ...