Part one of term paper
Down syndrome is one of the most frequently occurring birth defects in the world. It is a chromosomal abnormality which results in 47 chromosomes, instead of 46, with an extra chromosome being 21. Because the majority of Down syndrome cases affect the twenty-first chromosome, it is commonly called "trisomy 21." Down syndrome is usually caus ...

Part two of term paper
... there seems to be some relatedness to maternal age. There are two other types of Down syndrome, mosaicism and translocation, but these do not affect individuals as frequently as non-disjunction. Mosaicism is a mixture of two cell types, leaving the individual with some normal chromosomes of 46, and some affected ones with 47. Translocation occurs when part of the twenty-first chromosome breaks off and attaches to another cell. The total number of chromosomes is 46, however the excess ...