ABSTRACT
Human chromosomes have been analyzed for research and diagnostic purposes for over 50 years. Chromosome structure and behavior are relevant in both mitosis and meiosis. However, when human chromosomes are studied under the microscope it is almost always during mitosis. The introduction of techniques that revealed chromosome banding patterns allowed each individual chromosome to be identified, and permitted more accurate definition of chromosomal abnormalities. Chromosomal abnormalities too small to be seen under the microscope were long suspected to be the cause of a number of unexplained recurrent syndromes and also of many individual cases in which a patient had a unique pattern of abnormalities. This chapter describes a range of abnormalities involving wrong numbers or structures of chromosomes or that, like gene conversion, are produced by essentially chromosomal mechanisms. It also describes genetic abnormalities that affect the phenotype of a person.
