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The chromosome complements of human/mouse hybrid cell lines of mouse 3T3-4E and RAG parentage have been analyzed using chromosome banding methods. Three lines that were susceptible to lytic infection with poliovirus contained eleven to seventeen human chromosomes, including chromosome 19. Polio-resistant sublines of these contained no chromosome 19 and showed no other consistent change in the complement of human chromosomes. Human chromosome 19 therefore is essential for polio-sensitivity. Since polio sensitivity was correlated with receptor activity in these lines, we conclude that chromosome 19 carries the structural gene for the poliovirus receptor. Sensitivity to echo-7 and Rhino-1A viruses could not be related to the presence of a specific human chromosome.

Metaphase chromosome preparations of three male and one female Gorilla gorilla were stained to demonstrate quinacrine, Giemsa, centromeric heterochromatin, and, in one case, reverse-Giemsa bands. A standard karyotype is proposed based on chromosome banding pattern, centromeric index, and length. Three types of variation between homologous chromosomes are described: presence or absence of very bright fluorescence of the short arm or satellite region of acrocentric chromosomes, presence or absence of bright quinacrine bands at the distal ends of chromosome arms, and large differences in the size of the heterochromatic region on each of two biarmed chromosomes. At least half the chromosome pairs show polymorphisms of these types. Satellite associations were scored for each animal. In one case the two smallest pairs of chromosomes were preferentially involved in associations.

Banded karyotypes were prepared for three independent sublines of clone 745A, a Friend virus-induced erythroleukemia cell line originally produced by Dr. C. Friend. Each subline had the same chromosome complement, with a near-diploid number of chromosomes, two-thirds of which appeared normal. The remaining one-third were structurally rearranged marker chromosomes, including eight whose origins could be determined from their banding patterns. A fourth subclone of line 745A, under different selection pressure, showed changes in five marker chromosomes but no changes in the normal chromosomes, suggesting that the markers contained unstable sites, perhaps viral integration sites. Another Friend virus-induced erythroleukemia cell line, FSD-1/F4, developed independently by Dr. W. Ostertag, had a near-diploid number of chromosomes, about one-fourth of which were abnormal chromosomes. The only similarity between these markers and those in subclones of 745A, other than participation of some of the same chromosomes in centric fusion, was the inclusion of the proximal two-thirds of chromosome 15 in one of the markers of each line. This adds to the number of mouse tumor cells or cell lines in which No. 15 is altered or duplicated. In FSD-1/F4 cells there was a striking increase in the size of the secondary constriction of one of the two chromosomes 19, suggesting that the rRNA genes on this chromosome had been amplified.

Differences in the number of chromosomes with secondary constrictions and in the size of the C-band region on certain chromosomes have been observed among the following inbred strains of Mus musculus: C57BL/10J, C57BR/cdJ, DBA/1J, CBA/J, BALB/cJ, and AKR. These differences are useful as indicators of the location of rRNA genes and as normal chromosome markers. The size of each C-band region appears to remain constant over many generations. Only one probable change in the size of a C-band region was found.

Chromosomes of the owl monkey, Aotus trivirgatus, with 2n = 54, 53, or 52, have been stained to show quinacrine (Q-) and Giemsa (G-) bands, and a karyotypic arrangement has been proposed based on lengths, centromeric index, and banding pattern. C-bands were present at the centromeric region of every chromosome and over the entire short arm of certain acrocentric chromosomes; 5-methylcytosine was concentrated in the same regions. Bright Q-bands at the telomeric ends of the short arms of some chromosomes probably represent a second type of repetitive DNA. Ag-staining showed that only the chromosomes bearing a secondary constriction are nucleolus organizer chromosomes.

Metaphase chromosome preparations were made from leukocyte cultures of normal individuals. The cells were fixed in methanol:acetic acid (3:1 v/v), then dropped on cold, wet slides which were air-dried before storage at 4 degrees C. The slides were stained to identify the chromosomes by one of the following procedures: (1) Quinacrine. Slides were stained for 10 min in quinacrine mustard solution, rinsed in running tap water for 2 min, and mounted in Tris-maleat buffer, pH 5.6.

Quinacrine (Q-band) and centromeric heterochromatin (C-band) patterns of metaphase chromosomes of two subspecies of Mus musculus were compared. M. m. musculus (the laboratory mouse) and M. m. molossinus (a subspecies from Southeast Asia) had similar Q-band patterns along the length of the chromosomes, but differences were observed in the centromeric region of some chromosomes. The two subspecies had very different distributions of C-band material. Antibodies to 5-methylcytosine were bound to regions of the chromosome corresponding to the C-bands in each animal. These findings support the idea that satellite DNA, which is concentrated in the C-band region, changes more quickly than bulk DNA. The interfertility of these two subspecies permits the development of a musculus strain carrying normal marker chromosomes for genetic studies.

Silver staining has been used to detect active nucleolus organizer regions (NOR's). By this criterion six mouse chromosomes, numbers 12, 15, 16, 17, 18 and 19, can have an NOR. The number and distribution of chromosomes with NOR's vary among inbred strains of Mus musculus musculus (C57BL/6J, BALB/cJ, C3H/HeJ and C3H/StCr1BR) and in M. musculus molossinus. In a musculus x molossinus F1 hybrid, nucleolus organizers from each parent are silver stained.—Chromosomes which have NOR's in diploid cells also show them in tetraploid cells and in established cell lines. The BALB/cJ strain shows Ag-staining of NOR's on chromosomes 12, 15, 18 and occasionally 16. In the RAG cell line, which was derived from BALB/c, active NOR's are seen on 12, 15 and 18, even after these chromosomes have undergone structural rearrangements in the cell line. Some correlation exists between the amount of Ag-stain and the size of a secondary construction region, with a large amount of Ag-stain present on a chromosome which has a prominent secondary constriction. There is no correlation between the amount of Ag-stain and the presence or absence of C-band material.

The H-Y locus is on the short arm of the human Y chromosome in most individuals but on the long arm in at least one of 17 individuals with structural abnormalities of the Y.

Fixed metaphase chromosomes of gorilla and chimpanzee were UV-irradiated to produce regions of single-stranded DNA and then treated with antibodies specific for the minor DNA base 5-methylcytosine (5 MeC). An indirect immunofluorescence technique was used to visualize sites of antibody binding. In the gorilla six pairs of autosomes contained major fluorescent regions, indicating localized regions of highly methylated DNA. These corresponded, with the exception of chromosome 19, to the major regions of constitutive heterochromatin as seen by C-banding. The Y chromosome also contained a highly fluorescent region which was located just proximal to the intense Q-band region. In the chimpanzee no comparable concentrations of highly methylated DNA were seen. Smaller regions of intense 5 MeC binding were present on perhaps six chimpanzee chromosomes, including the Y. Five of these corresponded to chromosomes which were highly methylated in the gorilla.--There is diversity among the human, gorilla and chimpanzee in both the size and location of concentrations of 5 MeC, supporting the idea that satellite DNA evolves more rapidly than DNA in the remainder of the chromosome.

A human fibrosarcoma line, HT1080–6TG, with a near diploid number of chromosomes, has an average of 7.3 chromosomes with an Ag-stained nucleolus organizer region (NOR). Cells of this line with an increased number of chromosomes have an increased number of Ag-stained NORs. This cell line has been used as the human parent in constructing mouse-human and rat-human hybrids that segregate rodent chromosomes. The hybrid cell lines, which have 100 or more chromosomes per cell, show a proportionate increase in the number of Ag-stained NORs (means, 11.4–16.8). The frequency of association of acrocentric chromosomes increases in a similar fashion. There is no evidence of inactivation of human NORs in these cells.

THE wood lemming, Myopus schisticolor Liljeborg, is distinguished by an aberrant sex ratio, with a considerable excess of females, and by the fact that some females produce only daughters1,2. Fredga and his associates3 have provided a basis for understanding both these characteristics. They observed that 82 out of 181 female wood lemmings studied (45%) had an XY sex chromosome constitution, with chromosomal G-banding and C-banding patterns indistinguishable from those of XY males. On the other hand, the XY females were anatomically normal and indistinguishable from XX females. Furthermore, meiotic studies3 showed that the germ line in the somatically XY females was XX. The second X chromosome in the germ cells must have arisen by non-disjunction from the single X present in the XY cells. Thus all progeny from such females must have received copies of the same X chromosome. How does one reconcile these observations with the apparent function of the Y chromosome in mammalian sex determination4, or with more recent evidence that a particular Y-linked gene which controls presence of H–Y antigen is critical for differentiation of the male gonad? We have approached these questions serologically by typing male and female wood lemmings for expression of H–Y antigen, and we have found that all female wood lemmings are H–Y−.

A deletion of the albsino (c) locus on mouse chromosome 7 has been demonstrated using Q- and G-banding methods in a mouse heterozygous for the radiation-induced lethal albino allele, c 25H . The deletion, which is thought to be 1-6 cM long, represents about 7.6% of the length of the metaphase chromosome.