Chromosomes

Graham C. Webb

The University of Adelaide, Australia

Chromosomes in insects display almost the whole range of variation seen in the chromosomes of higher plants and animals. In these groups the deoxyribonucleic acid (DNA), which contains the genetic code determining development and inheritance, is contained in a nucleus in each cell. At interphase, the DNA is organized into the complex linear structures that are chromosomes, which can be seen in a conveniently condensed state when the cell is dividing.

The study of insect chromosomes is less intensive now than formerly for three possible reasons: (1) the thoroughness of the early investigators, (2) the commercialization of science, which has pushed the study of chromosomes (cytogenetics) in animals toward more lucrative mammalian, and particularly human, fields, and (3) the replacement of cytogenetic with molecular methods. The third point was predicted by Michael White in the conclusion to his famous 1973 textbook, Animal Cytology and Evolution. Through his work, almost entirely on insects, White is widely regarded as the founder of the study of evolutionary cytogenetics in animals and one of its foremost authorities; his book remains a most comprehensive authority on most aspects of insect chromosomes.

In 1978 White was firmly convinced that evolution is essentially a cytogenetic process, and he did much to demonstrate this at the level of speciation. At a higher evolutionary level, the integrated chromosomal characteristics of the various insect orders seem to support this view. However more recently authors such as King have de-emphasized the importance of chromosomal changes in species evolution.

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