The functional units of macronuclear assortment inTetrahymena thermophila

Abstract

Macronuclei assorting simultaneously for H, Chx, Mpr, and co, and containing only one or two copies of the H D allele produced several combinations of phenotypes at the other loci, instead of only one or two such combinations. It follows that macronuclear subnuclei, if they exist at all, must frequently exchange parts. Models involving somatic recombination, transient subnuclei, or progressive chromosome fragmentation are discussed as possible explanations.

Variability in the timing and outcome of macronuclear assortment inTetrahymena thermophila

“…Reference will be made to theoretical predictions (Doerder et al 1975, 1977, andunpublished) included in tabular form in the preceding paper. Marker phenotypes for Chx, Mpr, co, and ts-1 are described in the previous paper (McCoy, 1979). The H locus has a number of alleles identified by the immobilization and agglutination of cells when exposed to a characteristic monospecific antiserum (Nanney & Dubert, 1960).…”

“…Procedures follow exactly those cited previously (Allen & Gibson, 1973;McCoy, 1979). The few modifications used here will be mentioned as individual experiments are discussed.…”

“…While the temporal problem remains very real, there is evidently more involved than simply commencing assortment for a given locus after a set number of fissions have elapsed. The use of the multiple marker stocks described in earlier papers (McCoy, 1977(McCoy, , 1979 also revealed other new features of assortment. Probably the most interesting of these is the existence of a continuum of input ratio and determination time.…”

Discrete length of palindromic segments from Tetrahymena DNA

“…A possible rearrangement of large palindromes in Xenopus Zaevis DNA was also suggested [ 121. Intramacronuclear recombination events may explain the number of phenotypic combinations of several markers during vegetative propagation of Tetrahymena thermophila [5].…”

“…The palindromic segments are discrete in length. Possible functions of these DNA segments are discussed in connection with some recombination events in the Tetrahymena genome [5].…”