Molecular genetics is the study of chromosomes and the related disease states caused by abnormal chromosome number and/or structure. Chromosomes are complex structures located in the cell nucleus, they are composed of DNA, histone and non-histone proteins, RNA and polysaccharides. They are basically the “packages” that contain the DNA. Normally chromosomes can’t be seen with a light microscope but during cell division they become condensed enough to be easily analyzed at 1000X. To collect cells with their chromosomes in this condensed state they are exposed to a mitotic inhibitor which blocks formation of the spindle and arrests cell division at the metaphase stage. A variety of tissue types can be used to obtain chromosome preparations. Some examples include peripheral blood, bone marrow, amniotic fluid and products of conception.