A Study of Early Events in Ribosomal Gene Amplification
This extract was created in the absence of an abstract.
Excerpt
During most of oogenesis in Xenopus laevis, the ribosomal RNA genes are amplified well above their normal chromosomal level (reviewed by Gall 1969; Macgregor 1972; Tobler 1975). The first burst of extra rDNA synthesis occurs in both sexes when only 9–16 primordial germ cells are present (Kalt and Gall 1974), and the resulting 10- to 40-fold increase in ribosomal RNA gene number is maintained throughout gonial cell proliferation until meiosis begins (Pardue and Gall 1972). At meiosis the sexes differ. In the male, all detectable amplified rDNA is lost, but in the female there is a transient reduction in rDNA followed by a dramatic second wave of amplification to about 2500 times the chromosomal rDNA level (Gall 1968; Macgregor 1968; Evans and Birnstiel 1968; Brown and Dawid 1968). It is this second wave of amplification that has been most thoroughly studied and is now known to involve a rolling-circle replication...
