Chromosomal arrangement of the two main rDNA size classes of Ascaris lumbricoides.

The two main rDNA size classes of 8.8 kb and 8.4 kb length from Ascaris lumbricoides, which comprise more than 95% of the total nuclear rDNA, are arranged as internally homogeneous clusters and are not intermingled with each other. The rRNA genes are present on a single autosomal locus as could be demonstrated by in situ hybridization of fluorochrome-labelled 18S and 26S rRNA to metaphase chromosomes of spermatocytes I. The quantitative ratio of the two rDNA size classes varies largely between individuals being on the average roughly 10:1 in the investigated wild population of A. lumbricoides. However, there are no differences in the hybridization pattern of the two rDNAs in the DNA eliminating nematode A. lumbricoides between germ line and somatic cells in any of the individuals that have been analyzed.