PARTIAL TRISOMY

There is a small extra piece of a chromosome attached to anotherchromosome. This may be called an unbalanced translocation.

MOSAICISM

This is an error in the cell division after the fertilised egg splits into two cells.

There is an extra chromosome in some cells but not in others. The cells with 45 chromosomes die.

RING CHROMOSOMES

In rare cases chromosomes can form rings due to loss of genetic materialfrom both ends of the chromosome. Cell divisions during the developmentof the embryo, fetus, child, and adult, may involve further damage to thering chromosome, and generally this cell division happens at a lower rateand body growth is slowed.

DELETIONS

A deletion means that there is part of a chromosome missing. The long armof the chromosome is referred to as q, and the short arm as p. A deletion ofthe long arm of chromosome 13 would be 13q-, and numbers can be usedto specify exact areas of the chromosome.