Giant chromosomes. Colured scanning electron micrograph (SEM) of giant (polytene) chromosomes from a fruit fly (Drosophila busckii). These chromosomes are formed from repeated rounds of DNA (deoxyribonucleic acid) replication without nuclear division. A process known as endoreduplication. Identical strands sit side by side. he characteristic banding pattern corresponds to areas of high and moderate DNA density. The polytene chromosomes increase cell volume and metabolic rate, as there are more genes to be expressed. The size of the chromosomes also allows for easy study by scientists. Magnification: x700 when printed at 10 centimetres wide.