Measurements of the genome size of the monogonont rotifer Brachionus plicatilis and of the bdelloid rotifers Philodina roseola and Habrotrocha constricta

Abstract

Genome size may be determined as the mass of genomic DNA per copy of a given sequence, multiplied by the number of copies of that sequence in the genome. Practical application of this relationship may be made by hybridizing a radiolabeled cloned segment of the genome to a known number of copies of the segment and to a known mass of genomic DNA separately immobilized on the same membrane. The ratio of the hybridization intensity per copy of the segment to the hybridization intensity per unit mass of genomic DNA is then taken to be the mass of genomic DNA per hybridizing sequence present in the genome. This ratio multiplied by the number of hybridizing sequences in the genome, determined by other means, is taken as the genome size. Employing this procedure with segments of the hsp82 heat shock gene cloned from the monogonont rotifer B. plicatilis and from the bdelloid rotifers P. roseola and H. constricta, we estimate their genome sizes as 0.7, 2.2 and 1.0 pg, respectively.