chapter  8
12 Pages

Micronuclei and Macronuclei

As we have seen, the diploid micronucleus undergoes mitosis at binary fission and meiosis at autogamy and conjugation. Measurement of the relative amounts of DNA in the micronucleus and macronucleus of P. tetraurelia has been done on individual cells using a microspectrophotometer after Feulgen staining, which is specific for DNA.1 These data were confirmed by Woodard et al.2 and produced a value of 430 times as much DNA in the macronucleus as in the micronucleus, or 860n for the macronucleus and 2n for the micronucleus. Similar results were obtained by Gibson and Martin3 for various species in the P. aurelia complex. Thus, while the micronucleus appears to be diploid, the macronucleus is highly polyploid. Micronuclear polyploidy, as well, has been demonstrated for several species of paramecia. See the review by Raikov.4