Amplification of ribosomal DNA in Acheta

In the Feulgen-stained nuclei of Acheta domesticus the amplification regions show up at early pachytene as 5 major chromomeres. In the light and electron microscopes, they are structurally alike, containing both a central core consisting mainly of DNA and an outer region rich in RNA. Of these five major chromomeres three release their DNA copies rapidly. The two remaining major chromomeres do not release their copies so rapidly and for this reason can be localized in the autosomes Nos. 6 and 11 respectively. The frequency and the diameter of these chromomeres was recorded. The amount of DNA released from the chromomeres has been measured directly on the Feulgen-stained pachytene chromosomes. In the major chromomere of chromosome No, 6 the amount of DNA from early to late pachytene remains practically constant: the values are 2.00, 2.23, 2.16 and 2.20 picograms respectively. In the major chromomere of chromosome 11, which releases its copies during these stages, the values in picograms are: 1.48 (early), 0.27 (middle), 0.11 (late 1) and 0.05 (late 2 pachytene). The present results support the view that given chromomeres in Acheta are not only spiralized regions of the chromosome but are also regions containing amplified DNA copies. Moreover, these findings have three genetic implications: (1) chromomeres release DNA copies during different stages of meiosis, (2) they contain amplified genes and (3) are regions which show “puff” formation essentially similar to that of the bands of salivary gland chromosomes.