K.C. Atwood

Variation in the number of genes for rRNA among human acrocentric chromosomes: correlation with frequency of satellite association

Grain counts after hybridization of 125I-rRNA to human chromosomes indicate numerical polymorphism at the rDNA sites. Prephotographing procedures decrease labeling but do not change the proportions of labeled RNA annealed to different chromosomes. A positive correlation was found between the frequency of participation of a given chromosome in satellite associations and its rDNA content by the criterion of grain count. Certain individual chromosomes are clear exceptions to this correlation.

The chromosomal location of ribosomal DNA in the mouse

In situ hybridization of I125-labelled ribosomal RNA to mouse chromosomes was used to determine the location of the rDNA loci. The results demonstrate the presence of rDNA sites on chromosomes 15, 18 and 19.

Variation in ribosomal rna gene number in mouse chromosomes.

Hybridization of 125-I-ribosomal RNA to mouse chromosomes in situ produced significant differences in grain count at known rDNA sites, depending on the strains from which they were derived. This is interpreted to mean that the number of rRNA genes in a given nucleolar chromosome, and in the entire genome, is polymorphic among strains and among outbred individuals.

Localization of rDNA and Giemsa-banded chromosome complement of white-handed gibbon, Hylobates lar.

A karyotype based on banding pattern and chromosome length is presented for the white-handed gibbon, Hylobates lar. Little homology with the banding patterns of the chromosomes of the other Hominoidea can be seen, confirming the early evolutionary separation of Hylobatidae and the other apes. Hybridization in situ with ribosomal RNA shows that the secondary constriction of a submetacentric chromosome (15) is the only site of the nucleolar organizer, as in the Cercopithecoidea. The correlation of polymorphic variation in size of this secondary constriction with grain density suggests differences in the number of gene copies per chromosome.

Localization of rDNA in the chromosome complement of the rhesus (Macaca mulatta).

In situ hybridization was used to identify the region of the Rhesus genome complementary to ribosomal RNA. The rDNA sites have been assigned to the achromatic region of chromosome 20.

Localization of rDNA in the chimpanzee (Pan troglodytes) chromosome complement

In situ hybridization was used to identify the sites of rDNA in the chromosome complement of the chimpanzee (Pan troglodytes). The rDNA was present in the satellite regions of chimpanzee chromosomes 14, 15, 17, 22 and 23. Four of these (14, 15, 22, 23) are homologous to human chromosomes carrying rDNA: 13, 14, 21 and 22.

Chromosomal distribution of rDNA in Pan paniscus, Gorilla gorilla beringei, and Symphalangus syndactylus: Comparison to related primates

Hybridization in situ was used to identify rDNA in chromosomes of the pygmy chimpanzee, mountain gorilla, and siamang gibbon. In contrast to other Pongids, and man, the gorilla has only two pairs of rDNA-containing chromosomes. The single pair in the siamang bears no resemblance to the nucleolar chromosome of the closely related lar gibbon. Pan paniscus and P. troglodytes have the same rDNA distribution, and similar karyotypes except in the structure of chromosome 23p. Grain counts over unbanded preparations show that the human, orangutan, and both chimpanzees have about the same total rDNA multiplicity.

The chromosomal location of rDNA in selected lower primates

Hybridization in stiu was used to identify the chromosomes that carry rDNA in representative lower primates, including the baboons, Papio cynocephalus and Papio hamadryas; the colobus monkey, Colobus polykomos; the tree shrew, Tupaia glis; the lemur, Lemur fulvis; the saki, Pithecia pithecia; the marmoset, Saguinus nigricollis, and the spider monkey, Ateles geoffroyi. The marker chromosome, common to the Cercopithecines studied to date, carries the rDNA in the baboons. Another marker chromosome carries rDNA in a South American species, the spider monkey. A multichromosomal distribution of rDNA was demonstrated in the tree shrew, lemur, saki, and marmoset. None of the rDNA-containing chromosomes in the prosimians and New World monkeys show homology to the chromosomes that carry rDNA in the Hominids, Pongids, or Old World monkeys.

The site of 5S RNA genes in primates

A major site of genes for 5S RNA has been localized in representative members of the family Pongidae by means of hybridization in situ. These genes are shown to be concentrated in the most distal bands of the primate chromosome arm homologous to human chromosome 1q.

The site of 5S RNA genes in human chromosome 1

The major site of genes for human 5S RNA is in the long arm of chromosome 1. We find no evidence of sites in other chromosomes; if such exist, they are much smaller than the site in 1q.