Chemistry

Eukaryotic chromosomes are long molecules of DNA wrapped around proteins; only part of this DNA codes for proteins; noncoding DNA is not translated
About 1% of eukaryotic DNA is expressed as protein
Prokaryotes, including bacteria, have a single circular chromosome with little associated protein, they don’t have introns, and an estimated 90% of their DNA is translated; many bacteria also have plasmids ; which are small circles of DNA that contain additional genes
Genetic engineers use plasmids to introduce modified genetic material into bacterial cells; plasmids also can carry genes that provide resistance to antibiotics
Chromosomes are easiest to study in the condensed form they have during cell division
Chemicals are added to cultured white blood cells, in order to make them stop in metaphase
Individual chromosomes can be cut out of an enlarged photograph and arranged by size and shape to form a display called a karyotype