Variation of relative chromosome lengths in mammalian karyotypes: A hypothesis of equalizing selection

摘要

A hypothesis on the elective neutrality of relative lengths of karyotype chromosomes was tested. Idiograms expected based on an assumption of selective neutrality ofb chromosoem lengths were compared with actual idiograms in more than a hundred mammalian species. The observed idiograms differed from those expected in a similar manner, in the observed idiograms, the longest chromosomes were shorter, and the shortest were longer than expected. It is suggested the karyotype chromosome variation is limited by selection against chromosome rearrangements that produce very long or very short chromosomes. An analysis of reciprocal translations in the mouse and Drosophila showed that translations generating chromosomes of extreme lengths were more deleterious than those generating normal-sized chromosomes. A working hypothesis was advanced stating that within-karyotype variation of chromosoem lengths is accounted for by two factor; chromosome rearrangements and natural section: chromosome rearrangements tend to randomize relative chromosome lengths in a karyotype, whereas natural selection acts to equalize them.