Large Autosomes Research Articles

Chromosome banding and phylogenetics of the golden mouse, Ochrotomys nuttalli

The number and location of nucleolus organizer regions, and G- and C-band karyotypes of Ochrotomys nuttalli were compared with those of other seemingly closely related New World peromyscine rodents. Although Ochrotomys was once considered a subgenus of Peromyscus, it shares few apparent G-band homologies with any peromyscine. The presumed homologous karyotypic elements shared between Ochrotomys and other peromyscine genera also are shared with Neotoma (the probable sister group of peromyscines) and these elements are hypothesized to be primitive for the group. The largest autosome in Ochrotomys appears to be shared with a distantly related species, Sigmodon hispidus, and this chromosome might be represented as two acrocentric autosomes (tandem fission products) in peromyscines and Neotoma. If this hypothesis is correct, the peromyscines as currently recognized likely are polyphyletic. The unusually extensive rearrangement of the Ochrotomys karyotype relative to peromyscines appears to represent a case of karyotypic megaevolution.

In vivo sister chromatid exchanges in the euchromatin and constitutive heterochromatin of the Indian mole rat, Nesokia indica.

Distribution of in vivo SCEs in euchromatin and constitutive heterochromatin of Nesokia indica has been studied. The distinct partitioning of the euchromatin and constitutive heterochromatin into different arms of the large X chromosome greatly facilitates such a comparison. The constitutive heterochromatin showed a higher SCE rate per unit length than the total euchromatin. However, between the two types of chromatin in the X itself there was no significant difference. These values were also comparable to that observed for the largest autosome. This study suggests that factor(s) other than chromatin condensation, DNA base composition, and DNA replication kinetics is (are) responsible for the formation of SCEs.

Two Types of Y Chromosome in a Brazilian Cattle Breed

SUMMARYLymphocyte cultures from 56 males of the Brazilian Ibage breed, formed by crosses between Bos indicus and Bos taurus, reveal the co-existence of the acrocentric and submetacentric Y characteristic of Asian and European cattle respectively. The G and C bands support the hypothesis put forward previously that these two types of Y originated through a pericentric inversion. In one animal, one of the large autosomes (probably no. 6) was heteromorphic for the centromeric heterochromatin. The C bands of the Y in cattle are unusual; apparently contradictory results obtained by previous authors may be due to a peculiar sequence and composition of the nucleotides in the DNA of this chromosome in this organism.

The brood pattern of mitomycin-c-induced translocations in Drosophila melanogaster males: the effect of time.

Translocations between the two large autosomes were scored in the progeny of males that had been fed mitomycin-C. The frequencies were the same in spermatogonia sampled after 12 and 25 days and in spermatozoa stored for the same periods in untreated females.

Chromosome polymorphism in populations of the grasshopper Trimerotropis pallidipennis from southern Argentina

Three populations of the grasshopper Trimerotropis pallidipennis from southern Argentina have been studied cytologically. A very characteristic B-chromosome was found in all three. They also showed geographical variability in respect of the presence of pericentric inversions, and the inversion system was found to influence chiasma frequency. The Laguna Blanca population, which is on the hypothetical pathway the species is believed to have followed during its migration from northern to southern latitudes, has the same karyotype composition as the N. American form, with fixed inversions in the 3 largest autosomes and the X-chromosome. Its members have a high total chiasma frequency and a great number of interstitial chiasmata. The Sierra de la Ventana population, situated at the absolute eastern border of the species distribution is highly polymorphic with respect to the presence of inversions in the medium chromosomes. Its members have the lowest total chiasma frequency and a greatly reduced number of interstitial chiasmata. Situated geographically between the other two, the Choele-Choel population has the highest frequency of inversions and many of them are homozygous. Its members have a higher total chiasma frequency than that observed in specimens from Sierra de la Ventana, and a greatly reduced number of interstitial chiasmata, similar to that observed in individuals from the latter population.

Neo-XY Sex Chromosomes inZygoclistron Nasicum(Orthoptera-Acridoidea)

SUMMARYThe karyotype of Z. nasicum is described. It consists of 2n=20 ♂ (XY)-20 ♀ (XX), with a pair of large metacentric autosomes, a metacentric X and an acrocentric Y, the remaining autosomes being acrocentric. Both the metacentric autosomal pair and the XY♂- XX ♀ sex mechanism are present in all the species cytologically examined of Aleuas and Zygoclistron except an undescribed species of Aleuas where the metacentric autosome dissociated into two acrocentric chromosomes. So, an ancient and common origin for both the fusions involved is suggested.The coiling mechanism in the XY pair during the first meiotic division is of an unusual type in Z. nasicum.

Establishment and characterization of a cell line from the American opossum (Didelphys virginiana).

A permanent tissue-cultured cell line (designated OK) has been established from kidney tissue of an adult American opossum. The OK line has been characterized with respect to morphology, chromosome constitution, tissue-culture requirements, and attainable mitotic arrest. The cells are epithelial-like with a stable nondiploid chromosomal modal number of 23. Cells grown in Eagle's minimal essential medium with 10% fetal bovine serum have a mean doubling time of 18 hr. The cell line OK is potentially useful for the isolation and purification of the mammalian X chromosome because of the size differential between the smaller X's and the larger autosomes.

Characterization of two moderately repetitive DNA components localized within the ?-heterochromatin of Drosophila hydei

Two nuclear DNA fractions from Drosophila hydei were isolated by silver ion and actinomycin D binding and centrifugation in isopycnic salt gradients. Neither fraction is composed of nor does it contain any highly repetitive simple sequence DNA, as shown by melting and reassociation studies. — One fraction has a CsCl density of 1.702 g/cm3 and hybridizes in situ with the β-heterochromatin of the chromocenter in polytene cells. This DNA fraction was found to be replicated during polytenization. In diploid cells this 1.702 g/cm3 component hybridizes to the heterochromatin of all four large autosome pairs, the middle part of the long arm of the Y-chromosome, but not to the X-heterochromatin. — A second fraction has a CsCl density of 1.697 g/cm3 and hybridizes in situ with polytene cells to the chromocenter and the nucleolus, but on metaphase chromosomes only to the nucleolus organizer regions.

Heterochromatin variation in Cryptobothrus chrysophorus

The endemic grasshopper Cryptobothrus chrysophorus is widely distributed throughout S.E. Australia and its populations display an extensive and spectacular pattern of autosomal variation. While the standard telocentric complement of three long (L1–3), six medium (M4–9) and two short (S10–11) autosome pairs is present throughout most of its range, two quite distinct chromosome “races” can be defined within this species. Populations in the northern part of its distribution (northern N.S.W. and southern Queensland-northern “race”) are differentiated from the remainder (southern “race”) by fixed blocks of distal heterochromatin on autosomes M4, 5, 6, 8 and 9 and by differences in the character of the megameric M7 chromosome. Additionally, while many populations in both races show a polymorphic system of supernumerary segments on the two smallest autosomes (S10–11), that found in the northern “race” is both more variable and more complex. On the other hand all the populations of the southern “race” we have examined are polymorphic for a series of centric shifts which convert telocentrics into acro- or meta-centrics. These occur more commonly in the megameric M7 and the two smallest autosomes (S10–11) although in one population (Forbes Creek, N.S.W.) at least 12 different shifts involving 8 of the autosomes (L3, M4, 5, 6, 7, 8, 9 and S10) are known. By contrast, in the northern “erace” only the small autosomes (S10–11) show centric shifts. These several floating and fixed variants thus involve all chromosomes of the standard set other than the two largest autosomes (L1–2) and the X-chromosome, which appear to be invariate. Finally, morphologically distinct supernumerary (B) chromosomes, intermediate in size between the standard S10 and the M9 elements, are found in both “races” but are especially common in Tasmania, the most southerly point of the species range. These B-chromosomes are partly heterochromatic and partly euchromatic so that they too add to the considerable heterochromatin variation in this species.

Meiotic segregation of chromosomes in Drosophila melanogaster oocytes

A new technique was developed for a light microscopic analysis of meiosis in Drosophila oocytes. — When the nuclear envelope breaks down the bivalents, till then compressed into a karyosome, separate in early prometaphase. The homologues remain associated by chiasmata except for the fourth chromosomes which are no longer associated. Non-homologous chromosomes regularly segregating from each other in genetic experiments are also unconnected after karyosome disintegration but during metaphase I the fourth chromosomes and the heterologous pairs coorient on the same arc of the spindle and move precociously towards opposite poles. Nondisjunction and other irregularities are not infrequent in oocytes having an uneven number of achiasmatic elements. The fourth chromosomes and the Xs or the large autosomes, when lacking chiasmata, may be involved in non-homologous segregation. In c3G homozygotes all chromosomes appear as univalents in prometaphase. Segregation is variable but the observations suggest the polar distribution of equal numbers of chromosomes in variable combinations irrespective of the size. — Coorientation of univalents may be accounted for if the centromeres, whether homologous or non-homologous, are associated in pairs during early meiotic prophase, and that in the karyosome these pairing relationships are preserved until spindle organization at the onset of prometaphase.

Karyotypes and Meiosis of the Morabine Grasshoppers. I. Introduction and Genera Moraba, Spectriforma and Filoraba.

Moraba, with four species, has two showing the primitive 2nB = 17 karyotype and two in which the large metacentric AB autosome has undergone dissociation into separate acrocentrics. Spectriforma, also with four species (one cytologically unknown) shows the primitive karyotype. The single species of Filoraba likewise shows 2nB = 17, but its karyotype is distinctive, since one of the small autosomes has undergone an evolutionary diminution in size and is exceedingly minute. Members of these genera all have XO males. No cytological material of Drysdalopila, the fourth genus of the tribe Morabini (Key 1977), was available.

CHROMOSOMAL VARIATION IN THE PLAINS WOODRAT: GEOGRAPHICAL DISTRIBUTION OF THREE CHROMOSOMAL MORPHS.

Neotoma micropus ranges over most of the western two-thirds of Texas, the northeastern corner of Mexico, most of New Mexico, and parts of Colorado, Kansas, and Oklahoma (Hall and Kelson, 1959). An extensive chromosomal polymorphism has been reported in this species (Baker and Mascarello, 1969; Baker et al., 1970). Using regular karyotypic techniques (without banding), this polymorphism was found to consist of variation in the morphology of one pair of large autosomes. The morphology of this pair varied as follows: (1) both as acrocentrics (Morph I), (2) one as an acrocentric, the other a larger submetacentric (Morph II), or (3) both as large submetacentrics (Morph III). Mascarello and Warner (1974) examined C-band and G-band preparations from seventeen specimens of N. micropus and found that both an inversion and deletion within a block of constitutive heterochromatin are responsible for this polymorphism. Banded preparations showed the system to be a bit more complex than that described above. In fact, a fourth type of chromosome arrangement was noted in which there were two biarmed chromosomes. However, one (a subtelocentric) had a distinctly shorter second arm than the other (a submetacentric). None of the banded preparations were found to be homozygous for the subtelocentric condition. In addition to not being visible in regular karotypic preparations, the very short

Karyotype differences in the crenaticeps-group of Atractomorpha (Orthoptera, Acridoidea, Pyrgomorphidae).

The four known species of the crenaticeps-group of the genus Atractomorpha have 2n (male)=18+X0. All members of the complement are rod-chromosomes and the smallest autosome (no. 9) is megameric. The four species have similar amounts of euchromatin but differ markedly in the amount of heterochromatin present in their genomes. In A. similis, A. crenaticeps and the unnamed species, "Species-1", there are distinct proximal segments of heterochromatin in the eight large autosomes. In A. similis these chromosomes also have prominent distal segments of heterochromatin. The fourth species, A. australis, has no visible heterochromatin in its eight large autosomes except for a small segment at the proximal end of autosome 4. In all four species, the heterochromatic segments influence chiasma frequency and chiasma position. Moreover the overall chiasma frequency is lowest in A. similis with most heterochromatin and highest in A. australis with least heterochromatin.

A cytogenetical study of Glossina fuscipes fuscipes including a comparison of the polytene chromosome maps with those of Glossina austeni (Diptera, Glossinidae)

The male meiotic sequence is described for the tsetse fly Glossina fuscipes fuscipes together with the polytene chromosome maps and all principal cytological markers. The diploid chromosome number is 2n=6 and includes a pair of large submetacentric autosomes (L1), a shorter pair of metacentric autosomes (L2), and an X and Y which constitute a heteromorphic pair. Male meiosis is normally achiasmate although evidence is presented which suggests that chiasmata do form in about 1% of males. A detailed comparison between the polytene chromosomes of this species and Glossina austeni indicates that although they must have had a common ancestor, G. austeni is genetically more closely related to morsitans group tsetses.

Trisomy 8 Mosaicism Syndrome

Chromosome 8 is the largest autosome thus far found to be trisomic among liveborn infants. Trisomy 8 "mosaicism" syndrome (T8mS) consists primarily of individuals whose chromosome complement is mosaic for chromosome 8 (T8m), i.e., patients with a chromosomally normal cell line in addition to the trisomic 8 cell line, and a few known individuals with full trisomy 8 (T8), i.e., each cell observed contains an extra chromosome 8. Reported cases of both types share a number of common features and thus have helped to delineate a new syndrome. Common features of T8mS include mild-to-moderate mental retardation, strabismus, osseous and soft tissue abnormalities, lowset and/or malformed ears, broad bulbous nose, palate deformity, various types of congenital cardiovascular disorders, hydronephrosis, cryptorchidism, and characteristic dermatoglyphics. Since chromosomal mosaicism is often present in this syndrome it is not surprising that considerable phenotypic variation exists. The present report of one of the youngest individuals yet described with T8m adds two more physical findings (dense corneal clouding and a heretofore undescribed clavicular deformity) to the constellation of abnormalities associated with T8mS. On the basis of the phenotypic and cytogenetic findings in this and 17 similar patients previously reported it is proposed that T8mS is a distinct clinical entity.

Distribution among the chromosomes of Drosophila pseudoobscura of the genes governing the response to light.

Most strains of Drosophila pseudoobscura are neutral to light when tested in phototactic mazes. However, clear-cut photopositive and photogenative populations are obtained by selection over a series of generations. The genetic nature of the differences between the positive and negative populations has been studied in crosses in which the three large autosomes carried mutant markers. All chromosomes contain genes which influence the response to light. The third chromosome has the strongest effect, followed by the second, the X, and the fourth chromosomes. This seriation is not in proportion to the relative lengths of the chromosomes. Either the effective genes are not very numerous, or some of them exert stronger influences than others.

Karyotypic Variation in Peromyscus Boylii (Rodentia: Cricetidae) from Mexico and Corresponding Taxonomic Implications

Schmidly, David J., and Gilbert L. Schroeter (Department of Wildlife and Fisheries Sciences and Department of Biology, Texas AM the principal differences are in the numbers of large and medium-sized biarmed autosomes which range from 2-10. Three chromosome races are recognizable in P. boylii; they are distributed parapatrically with respect to one another, and present evidence suggests that limited gene exchange occurs among them. The karyotype for topotypes of P. b. simulus from Nayarit, Mexico, is markedly different from all other forms of P. boylii, suggesting that this taxon is a distinct species. Chromosomal polymorphism of a non-Robertsonian type is seen in certain populations of P. boylii and may be the result of intergradation between the different chromosome races. The polymorphism involves a variable number of large biarmed autosomes with certain individuals in a population possessing a heteromorphic pair of autosomes. The karyotypes of P. oaxacensis and P. evides, both members of the boylii species group, are also described for the first time. [Karotypic variation; Peromyscus boylii.] The brush mouse, Peromyscus boylii, is distributed from Honduras northward to Oregon and Utah and eastward to Texas and New Mexico. This species has the largest geographic distribution of any in the boylii species group (Hooper, 1968) and is among the most common of Mexican mice. Currently, 15 subspecies are recognized with the greatest differentiation occurring on the highlands of Mexico. Chromosomal data from 80 specimens of P. boylii, mostly from the western and southwestern United States, revealed significant geographic variation in the karyotypes of these populations (Lee, Schmidly, and Huheey, 1972). However, only 14 specimens of boylii were examined from western Mexico (Durango, Sonora, and Michoacan) and none was examined from northeastern Mexico. Moreover, all populations sampled by Lee et al. (1972) were monomorphic with regard to their chromosomal complement; for that reason, they suggested that P. boylii is chromosomally conservative. However, since different populations of P. boylii display such karyotypic diversity, it might be expected that populations do exist which are chromosomally polymorphic. Our subsequent data reveal the existence of an extensive intrapopulational chromosomal polymorphism of a non-Robertsonian type in Mexican populations of P. boylii. The polymorphism has been found in populations of the subspecies P. b. levipes, P. b. beatae, and P. b. spicilegus from the Mexican states of Queretaro, Hidalgo, Veracruz, and Durango. Furthermore, certain populations of P. boylii from Queretaro, San Luis Potosi, Tamaulipas, and Nayarit possess karyotypes distinct from other populations of this species. Chromosomal variation in P. boylii is herein reviewed in light of certain taxonomic problems in this

Location of the Pea Comb Gene

Two hybrid males were available, each having an X-ray induced translocation between the largest autosome and a Z chromosome. In one male the translocated genome was Single Comb White Leghorn. The other male had a Dark Cornish genome translocated. The genetic markers for this study were single comb from the Leghorn ancestor and pea comb from the Cornish ancestor.Observations of the chromosome structures and phenotypes of the progeny of these males when mated to similar hybrid females showed non-random distributions of comb types. From the data obtained it was concluded that the pea comb gene resides on the largest autosome in chickens and it probably is distally positioned on the longer arm.

KARYOLOGY OF NORTH AMERICAN NATRICINE SNAKES (FAMILY COLUBRIDAE) OF THE GENERA NATRIX AND REGINA

Four species of the water snake genus Natrix have a distinctly different pattern of chromosomal morphology than found in two species of the related genus Regina. Natrix all have a karyotype with seven pairs of large or medium-sized submetacentric autosomes, three pairs of medium-sized subtelocentric autosomes, and seven pairs of small metacentric autosomes. All have a 2n of 36 with a submetacentric Z and submetacentric or subtelocentric W. The autosomal complement of Regina consists of seven pairs of large to medium-sized submetacentrics, five pairs of medium-sized submetacentrics, and five pairs of small metacentrics. The Z and W are both submetacentric chromosomes. The sex chromosomes are easily distinguished in both genera. The relationships of Natrix and Regina and Old World Natrix are discussed, as well as chromosomal variation in closely related species in the family Colubridae.

Sex ratio distortion and semi-sterility in the progeny of irradiated Glossina morsitans.

SUMMARYMaleGlossina morsitanswere subjected to various doses of gamma radiation in air or nitrogen and mated to untreated females. The sex ratio of theF1progeny was biased towards males, and this may be explained by the extra vulnerability to dominant lethal induction that the presence of the largeXchromosome gives to female determining sperms. The mean fertility of theF1progeny was subnormal. This was due to the induction of 50 % sterility in a large proportion ofF1individuals. Cytogenetic examination of the progeny of outcrosses ofF1individuals indicated that in most of the semi-steriles there were translocations involving the large autosomes or theYchromosomes. Almost all the normally fertileF1flies gave only cytogenetically normal progeny. TheF1sex-ratio distortion and semi-sterility would provide a ‘bonus’ in the application of the sterile male technique, which would amount to a 15–50% saving in the releases required to achieve a population control target compared with the requirement if theF1was normal.