Chiasma frequency,distribution and interference maps of mouse autosomes

Chiasma frequencies were analysed and chiasma positions measured in diakinesis/metaphase I autosomal bivalents from oocytes and spermatocytes of F₁ hybrid C3H/HeH×101/H mice. Twenty chromosome size ranks, including the presumptive X bivalent, could be distinguished in oocytes, and nineteen autosomal ranks plus the XY pair spermatocytes. Overall, mean cell chiasma frequencies of the two sexes did not differ significantly once the contribution of the presumptive X bivalent and the XY pair were taken into account. Sex related differences in chiasma distribution patterns were evident, however. In monochiasmate bivalents, the chiasma was most commonly located interstitially in oocytes while in spermatocytes it could be either interstitial or distal. In dichiasmate bivalents, the chiasmata tended to be more centrally located in oocytes than in spermatocytes. Minimum inter-chiasma distances did not appear to show any great variation in chromosome pairs of different sizes, however, mean inter-chiasma distances did increase with the bivalent length. The minimum-inter chiasma distance data suggest that chiasma interference is complete over a chromosomal segment equating to approximately 60 Mb. Measurement of the positions of chiasmata along chromosome arms open up the possibility of producing chiasma-based genetic maps for all the autosomes of the mouse.     

Chiasma frequency and distribution in a maize family segregating for k10 and trisomy 10

Chiasma frequency was determined from total chiasma counts, and the distribution of these exchanges was determined by the ratio of proximal to distal chiasmata. No effect of trisomy 10 could be demonstrated. Confirmation was obtained of earlier work showing more proximal and fewer distal chiasmata in K10 plants than in controls. However, diakinesis data failed to confirm the ability of K10 to increase total chiasmata as suggested from metaphase I results.     

Quantitative analysis of C bands in chromosomes 1, 9, 16 and Y in Caucasian and Japanese males

A comparative analysis of the C bands of chromosomes 1, 9, 16 and Y of 27 Caucasian and 27 Japanese males is reported. The mean of the total centromeric heterochromatin of the three pairs (sigma h1, 9, 16) is larger in Caucasian than in Japanese subjects, but Caucasians showed a lower mean of C band size of chromosome Y. Heritability of the C band of the Y chromosome was studied in 26 families.     

Polymorphism of human chromosomes 1, 9, 16, Y: Variations,segregation and mosaicism

Summary A study was carried out on C-banded chromosomes 1, 9, 16, Y from an unselected population and from 30 normal families. We found: a) great variability in length and position of the C-bands; b) somatic mosaicism involving C-bands; c) variants in children that were not present in parental patterns. The possible role of crossing-over in generating the last two phenomena is discussed.     

Classification of qh regions in human chromosomes 1, 9, and 16 by C-banding

Summary We present a classification for secondary constriction (qh) regions with C-banding technique in chromosomes 1,9, and 16 by means of comparing them to the short arm of chromosome 16. It is simple and convenient and can be used routinely. It can be incorporated into the modified Paris nomenclature system.     

DNA polymorphism in a worldwide sample of human X chromosomes

DNA sequence data from humans can provide insight into the history of modern humans and the genetic variability in human populations. We report here a study of human DNA sequence variation at an X-linked noncoding region of 10,346 bp. The sample consists of 62 X chromosomes from Africa, Europe, and Asia. Forty-four polymorphic sites were found among the 62 sequences, resulting in 23 different haplotypes. Statistical analyses of the data led to the following inferences. (1) There is strong evidence of human population expansion in the relatively recent past, and this population expansion has had a significant effect on the pattern of polymorphism at this locus. (2) Non-African populations were unlikely to have been derived from a very small number of African lineages. (3) There was considerable geographic subdivision in the ancient human population, which could be an important reason why many studies failed to detect population expansion. (4) The long-term effective population size of humans is between 12,000 and 15,000. And (5) a non-African specific variant was found at a frequency of 35% in non-Africans, an estimate supported by the genotyping of additional 80 non-African and 106 African X chromosomes. This variant could have arisen in Eurasia more than 140,000 years ago, predating the emergence of modern humans. Moreover, this haplotype and all other haplotypes coalesced to the most recent common ancestor of the sample, which was estimated to be older than 490,000 years. Therefore, this region may have a long history in Eurasia.     

Spatial distribution of chromosomes 1 and Y in human spermatozoa.

The positions of chromosomes 1 and Y inside human spermatozoa were determined by differential staining techniques. In 85/100 cells the two chromosomes were in close contact and in association with a vacuole. This observation is in contrast to previous findings for chromosome No. 9 and the Y-chromosome whose positions do not appear to be correlated.     

Heterochromatic regions of human chromosomes 1, 9, 16 and Y and the phenotype

The relationship between variability of the heterochromatic regions of chromosomes 1, 9, 16, Y and the anthropometric characteristics (the height, the biacromial diameter and weight) was studied in two groups of children; 70 children had embryopathies of unknown etiology and 40 children had the Down syndrome. The positive statistically significant correlation of the C-segments lengths of chromosomes 1, 9, 16, their sum included, and above characteristics was found. The correlation coefficients of Y-chromosome were non-significant. The problems of functional role of the structural heterochromatin and its influence on viability and physical development of the organism are discussed.     

Chiasma frequency and position in male and female mice of chromosomes involved in homozygous and heterozygous translocations and tertiary trisomy

Chiasma frequency and position were analyzed at a predominantly late diplotene-diakinesis stage of the first meiotic division in oocytes and spermatocytes from T(1;13)70H homozygotes and heterozygotes, T(2;8)26H heterozygotes and from Ts(I¹³)70H tertiary trisomics of the mouse, Mus musculus. For T70H/T70H, the 13¹ long marker bivalent was studied and for the other karyotypes, analysis was confined to the multivalent configurations adopted by the rearranged chromosomes and their homologues. For the 13¹ bivalent, the chiasma frequency tended to be increased in the female. For the T26H and the T70H multivalents, the chiasma frequencies were higher in the female, largely due to the much higher values in the short interstitial segments. This observed enhancement has been attributed to pairing differences rather than to differences in chiasma forming capability. Both in the telomeric region of the 13¹ bivalent and in the short translocated segments of the reciprocal translocation and tertiary trisomic multivalents, females showed fewer chiasmata than males. The determinations of chiasma position in the 13¹ bivalent indicated chiasma interference with respect to position, leading to clustering of chiasmata somewhat beyond the centromere and towards the telomere of this chromosome.     

The quantitative analysis of polymorphism on human chromosomes 1, 9, 16 and Y

Summary The generalized characteristic of the C-segment lengths on chromosomes 1, 9, 16, and Y is suggested for a study of population heterogeneity. For this purpose, the concept of the distance D is introduced, taking into account the individual C-segment lengths, the mean lengths and standard deviations of C-segment lengths in a group of subjects, as well as the coefficients of correlation of the C-segment lengths on the said chromosomes.It is demonstrated that distance D may be employed to study the relevance of the given subject to the group studied, the relation to the mean characteristics within the group, and selection of subjects' pairs with almost identical C-segment lengths on respective chromosomes.In the study of such problems as zygosity of twins, family analysis, etc., along with the absolute C-segment lengths, it is recommended to employ the relative C-segment lengths on chromosomes 1, 9, 16, and Y, calculated as a part of the sum total of their absolute lengths.     

The quantitative analysis of polymorphism on human chromosomes 1, 9, 16, and Y

Summary A paracentric inversion of chromosome 5 was detected after RHG banding in a subject affected by Klinefelter's syndrome. The inversion was also observed in the patient's mother, and was confirmed by QFQ-and RBA-banding techniques.A second paracentric inversion affecting chromosome 7 was detected in a woman with Turner's syndrome. The same structural anomaly was found in her father and her half-brother.The possible relationship between sex chromosome nondisjunction and paracentric inversion is discussed.Furthermore, the inversion of chromosome 7 reproduces exactly the chromosome 7 of the gorilla, which is presumed to be ancestral to the human 7. This therefore appears to be the first reported case of reverse chromosomal mutation.     

The quantitative analysis of polymorphism on human chromosomes 1, 9, 16, and Y

This study was made to establish a stable quantitative characteristic of C segments on chromosomes 1, 9, 16, and Y in an individual karyotype that was reproducible in successive experiments. The C segment of these chromosomes were measured in successive cultures of cells from three males and the C segments of chromosomes 1, 9, and 16 in cells from three pairs of female monozygotic twins were measured. The results show that the absolute lengths of C segments tend to vary considerably with the cell samples analyzed, while the relative length, i.e., the length of a single C segment as a percentage of the total length of all C segments of the chromosomes being studied, is more stable and can be used for individual characteristics.     

Analysis of the inheritance of heterochromatic regions in human chromosomes 1, 9, 16 and Y

The inheritance of heterochromatic regions of chromosomes 1, 9, 16 and Y was studied in twelve families by means of measuring their C-segments. Maternal and paternal origin of chromosomes 1, 9 and 16 in the child was determined by two methods. The advantages and disadvantages of these methods and possibilities of their application are under discussion.     

Chiasma distribution in rye chromosomes of diploid rye and in wheat/rye addition lines in relation to C-heterochromatin

Summary In five genetically different inbred lines of rye and in the seven Chinese Spring/Imperial wheatrye addition lines, chiasma distribution in rye chromosomes was studied with respect to the amount and position of constitutive heterochromatin (Giemsa C-bands). In all inbred lines, rye chromosomes with one primary terminal band were more frequently found as univalents than those with primary bands on both telomeres. These chromosomes were most probably 5R and/or 6R. In the addition lines a highly significant reduction in the number of arms bound by chiasmata was found for rye chromosomes 5R and 6R. Because of the similar chiasma distribution in the inbred lines and in the rye chromosomes of the addition lines, no effect of the wheat genome on the number of chiasmata in the rye chromosomes can be ascertained. However, a relationship between chiasma frequency and chromosome arm length seems to exist, since under reduced chiasma conditions the two shortest arms of the rye complement, those of chromosomes 5R and 6R, frequently fail to form a chiasma. No effect of the large blocks of constitutive heterochromatin in the telomeres of the rye chromosomes on the position of chiasmata within a bivalent could be established.This study was financially supported by the Deutsche Forschungsgemeinschaft     

Discontinuities and unsynapsed regions in meiotic chromosomes have a trans effect on meiotic recombination of some chromosomes in human males

During meiosis, homologous chromosome pairing and synapsis are essential for subsequent meiotic recombination (crossing-over). Discontinuous regions (gaps) and unsynapsed regions (splits) were most frequently observed in the heterochromatic regions of bivalent synaptonemal complex (SC) 9, and we have previously demonstrated that gaps and splits significantly altered the distribution of MLH1 recombination foci on SC 9. Here, immunofluorescence techniques (using antibodies against SC proteins and the crossover-associated MLH1 protein) were combined with a centromere-specific fluorescence in situ hybridization technique that allows identification of every individual chromosome. The effect of gaps/splits on meiotic recombination patterns in autosomes other than chromosome 9 during the pachytene stage of meiotic prophase was then examined in 6,026 bivalents from 262 pachytene cells from three human males. In 64 analyzed cells with a gapped SC 9, the frequency of MLH1 foci in SCs 5 and 10 and in SC arms 10q, 11p and 16q was decreased compared to 168 analyzed cells with a normally-synapsed SC 9 (controls). In 24 analyzed cells with splits in SC 9, there was a significant reduction in MLH1 focus frequency for SC 5q and the whole SC5 bivalent. The positioning of MLH1 foci on other SCs in cells with gapped/split SC 9 was not altered. These studies suggest that gaps and splits not only have a cis effect, but may also have a trans effect on meiotic recombination in humans.     

Mitomycin C induced structural changes in heterochromatic regions of human chromosomes 1, 9, 16 and Y

Aberrations and variations in the heterochromatic blocks of chromosomes 1, 9, 16 and Y were found under the influence of mitomycin C in cultured lymphocytes of peripheral human blood. Lymphocytes were cultured during 96 hours, mitomycin C in final concentration of 0.3 mkg/ml was present in the culture during the latest 24 hours of culturing. Different changes in the heterochromatic regions of chromosomes were found in approximately 30% of cells: in 6.3% of cells mitotic chiasmata were indicated. In 9.5% of cells isolocus breaks were observed in heterochromatic region of chromosome 1 in segment 1q11. In the latter case this may be a fragile site detected under the influence of mitomycin C on the lymphocytes.     

Analysis of centromere size in human chromosomes 1, 9, 15, and 16 by electron microscopy.

Human chromosomes were treated with 5-azacytidine and analyzed by whole-mount electron microscopy. This base analogue produces undercondensation of heterochromatin and separation of the centromere from the bulk of pericentromeric heterochromatin in chromosomes 1, 9, 15, and 16, which allows clear delimitation of the centromere regions. A quantitative analysis of centromeres showed that chromosomes 1, 9, and 16 have centromeres of different size. The centromere of chromosome 15 is similar in size to that of chromosome 9 and different from those of chromosomes 1 and 16. No interindividual variation for centromere size was found. A positive correlation between centromere and chromosome size was found for the chromosomes analyzed.     

Loss of heterozygosity on chromosomes 1, 2, 8, 9 and 17 in cerebral atherosclerotic plaques

OBJECTIVE: Atherosclerosis is a fibroproliferative disease which has been attributed to several factors including genetic and molecular alterations. Initial studies have shown genetic alterations at the microsatellite level in the DNA of atherosclerotic plaques. Extending our initial findings, we performed a microsatellite analysis on cerebral atherosclerotic plaques. METHODS: Twenty-seven cerebral atherosclerotic plaques were assessed for loss of heterozygosity (LOH) and microsatellite instability (MI) using 25 microsatellite markers located on chromosomes 2, 8, 9 and 17. DNA was extracted from the vessels as well as the respective blood from each patient and subjected to polymerase chain reaction. RESULTS: Our analyses revealed that specific loci on chromosomes 2, 8, 9 and 17 exhibited a significant incidence of LOH. Forty-six percent of the specimens showed loss of heterozygosity at 2p13-p21, 48% exhibited LOH at 8p12-q11.2, while allelic imbalance was detected in 47% of the cases. The LOH incidence was 39%, 31% and 27% at 17q21, 9q31-34 and 17p13, respectively. Genetic alterations were detected at a higher rate as compared to the corresponding alterations observed in plaques from other vessels. DISCUSSION: This is the first microsatellite analysis using atherosclerotic plaques obtained from cerebral vessels. Our results indicate an elevated mutational rate on specific chromosomal loci, suggesting a potential implication of these regions in atherogenesis.