Unequal Crossover and the Evolution of Multigene Families
This extract was created in the absence of an abstract.
Excerpt
The 18 S and 28 S ribosomal RNAs in eukaryotes are coded by hundreds of identical or nearly identical genes which I will refer to coUectively as the rRNA family. There are about 500 such genes in the frog Xenopus laevis (Buongiorno-Nardelli et al., 1972) which I will assume to form a single cluster of tendemly repeated genes. The repeated unit in this rRNA family contains not only the “gene” portion, from which the rRNA molecules are transcribed, but also a “spacer,” which has no known function (Wensink and Brown, 1971; Miller and Beatty, 1969). Within one species of animal all the rRNA repeats are very similar or identical, but there are striking differences between the repeats in different species (Brown et al., 1972). Most of the interspecies differences reside in the spacer; the gene portion, which is presumably under more intense selective pressure, shows much less phylogenetic variation.
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