A high-resolution C-banding technique

A high-resolution C-banding technique is described. The major advantages of this method are its simplicity and reliability. Because this technique allows the recognition of unusual C-band heteromorphisms, it can be very useful in population cytogenetic studies.     

Human chromosomal heteromorphisms in Delhi newborns. II. Analysis of C-band size heteromorphisms in chromosomes 1, 9 and 16

Quantitative analysis of C-band size heteromorphisms in chromosomes 1,9 and 16 was carried out in 200 Delhi newborns (100 males and 100 females). The percent size heteromorphisms for chromosomes 1,9 and 16 showed nonsignificant differences between the sexes. Homozygous size level combinations showed higher incidence than the heterozygous combinations for all the three chromosome pairs studied in both sexes. Our results are compared with other reported studies and the possible role of these heteromorphisms in ethnic/racial variation and in developmental disturbances is discussed.     

Co-occurrences of polymorphic heterochromatin regions of chromosomes and effect on reproductive failure

Although the polymorphic heterochromatin regions of chromosomes (heteromorphisms) have been extensively studied for their phenotypic effects on humans, co-occurrences of chromosome 1, 9, 16 and Y heteromorphisms and of acrocentric variants have never been studied on humans with an objective scoring system. Here we compared the frequencies of individual heteromorphisms on a total of 602, 768 and 224 patients with the indications of infertility, recurrent miscarriage and in vitro fertilization (IVF) failure, respectively and on 272 controls. Then we examined whether there were significant co-occurrences between heteromorphisms within and between the groups. There were no statistically significant differences in the frequencies of heteromorphisms between the groups. Both statistically significant and non-significant correlations were observed within the non-acrocentric and certain acrocentric heteromorphisms in each group. When these co-occurrences were examined between the groups, a 2.2 fold increased risk of IVF failure in males in the presence of either chromosome 13 or chromosome 21 variants was observed (95 %CI:1.1–4.2). We conclude that the simultaneous manifestations of heteromorphisms have no effect on reproductive failure. There seems to be a correlation between the non-acrocentric heteromorphisms (1qh+, 9qh+, 16qh + and Yqh+/-), which might be the result of complex interactions of formation of these heterochromatin regions. The correlations observed between certain acrocentric chromosomes might be related to satellite association and nucleolus formation. The increased risk observed in males with IVF failure in the presence of either chromosome 13 or 21 variants should be interpreted cautiously due to the heterogeneity of the group.     

Prenatal diagnosis of a rare de novo centromeric chromosome 6 variant

Cytogenetic heteromorphisms are described as heritable variations at specific chromosomal regions without phenotypic effect. Polymorphisms of the size of heterochromatic centromeric regions of chromosomes 1, 9 and 16 have been well documented in humans but only four previous reports described centromeric polymorphism of chromosome 6. We present a prenatal diagnosis of a rare de novo centromeric chromosome 6 variant. Cytogenetic and molecular techniques were used to characterize this variant and confirm the de novo nature of this event. This case illustrates the importance of reporting unusual variant chromosomes for genetic counseling and for determination of the frequency of variant chromosomes in the general population.     

A cytogenetic survey of an institution for the mentally retarded

Summary Heteromorphisms of chromosomes 1,9, and 16 were studied by C-banding in a population of 403 mentally retarded individuals from diverse ethinic groups. A significant difference in the distribution of heteromorphisms was found among the different racial groups. The Orientals had a larger C-band on chromosome 1 and a smaller C-band on chromosome 9 than the other racial groups while the Caucasians had a larger C-band on chromosome 9. The Oriental group also had a significantly greater proportion of inverted C-band. No differences were found in the distribution of C-band heteromorphisms among different etiologic categories of mental retardation.     

Chromosomal heteromorphisms in Delhi infants. III. Qualitative analysis of C-band inversion heteromorphisms of chromosomes 1, 9, and 16

Qualitative analysis of C-band heteromorphisms was carried out in 200 infants (100 males and 100 females) in Delhi, India. Partial inversions minor and half inversions were observed as modal levels for chromosomes 1 and 9 in both sexes. No chromosome 16 with a C-band inversion was observed in the present investigation. A significantly higher incidence of percent inversions for chromosomes 1 and 9 was observed in males than in females. The frequency of heterozygous inversion level combinations for chromosome pairs 1 and 9 were remarkably higher than homozygous combinations both in males and females. Our results are compared with the other reported studies, and the possible role of these heteromorphisms in ethnic/racial variation and in developmental disturbances are discussed.     

Karyotyping and identification of human chromosome polymorphisms by single fluorochrome flow cytometry

Summary Frequency distributions of fluorescence intensity of ethidium bromide stained human chromosomes from nine phenotypically normal males are cross correlated and autocorrelated following repeated flow cytometric measurements. It is shown that each individual donor produces a fluorescence profile which is both visually and numerically different from those of other individuals in the set. The wide variety of chromosome heteromorphisms which occur to varying degrees for chromosomes 1, 9, 13, 14, 15, 16, 21, 22 and Y give rise to the uniqueness of a given fluorescence profile. Estimates of chromosome heteromorphisms for each individual in the set were made and then compared with parallel results obtained from inspection of Q-banded and C-banded conventional metaphase preparations. Fluorescence profiles identifiable with each individual were also obtained for Hoechst 33258 stained chromosomes.     

Minor chromosome variations and selected heteromorphisms in 200 unclassifiable mentally retarded patients and 200 normal controls

Summary Lymphocyte chromosome preparations from 200 mentally retarded children and 200 normal adult controls were analyzed by G-, Q-, and C-banding techniques for minor chromosome variations (G and Q) and selected heteromorphisms (G and C). Minor variations scored included inv(9), prominent or decreased short arms and/or satellite on acrocentric chromosomes, and 17ph. C heteromorphisms analyzed included those involving 1qh, 9qh, and 16qh regions. Length variations of Yq were scored on G-banded karyotypes. No significant differences in frequencies of scored minor variations or heteromorphisms were noted between the retarded and control populations.     

Human chromosomal heteromorphisms in american blacks

Summary One hundred normal American Blacks (B) were studied by sequential QFQ and RFA banding techniques in order to estimate the type and frequency of heteromorphisms. Color heteromorphisms were classified into one of six colors by RFA and intensity variation into one of five levels by QFQ. The data are compared with a previously studied Caucasian population (C). The frequencies of QFQ and RFA heteromorphisms were significantly higher in the Black than in the Caucasian population. No racial difference was noted for chromosome 21 by QFQ, while RFA demonstrated a clear difference. It is concluded that the maximum characterization of racial differences of human chromosomal heteromorphisms was far greater by RFA than with QFQ. The present study suggests differences in QFQ and RFA heteromorphisms among the two races.     

The long and short of sperm polymorphisms in insects

Production of more than one morphological type of sperm in a common testis has been documented for a variety of invertebrates, including gastropods, spiders, centipedes, and insects. This unusual phenomenon is difficult to explain by current theory, particularly since available evidence indicates that one sperm type is often incapable of effecting fertilization. In this review we critically examine evidence on the distribution and development of sperm heteromorphisms among insects in light of competing hypotheses for the evolutionary origin, maintenance, and function of a non-fertilizing class of sperm. To date, no single hypothesis, including alternatives which assume non-fertilizing sperm are non-adaptive, or that they provision, facilitate, or compete with fertilizing sperm, has received strong empirical support by any group of insects. The diversity of sperm heteromorphisms suggests that non-fertilizing sperm may have different functions in different clades or even serve multiple functions within a clade. We suggest that insight could be gained from (1) new models for the evolution of sperm polymorphism, (2) comparative studies that focus on multiple traits simultaneously (e.g. sperm number, proportion, length, and remating rate) and utilize clades in which more than one gain or loss of sperm heteromorphism has been documented (e.g. Pentatomidae, Carabidae, or Diopsidae), and (3) experimental studies that exploit individual variation or directly manipulate the composition of the male ejaculate.     

Satellite DNA and heterochromatin variants: The case for unequal mitotic crossing over

Summary Variations of constitutive heterochromatin (heteromorphisms) appear to be a general feature of eucaryotes. A variety of molecular and cytogenetic evidence supports the hypothesis that heteromorphisms result from unequal double-strand exchanges during mitotic DNA replication. Constitutive heterochromatin consists of highly repeated DNA sequences that are not transcribed. Thus, heteromorphisms are tolerated without overt phenotypic effect. Several of the highly repeated DNAs that comprise constitutive heterochromatin have been shown to contain site-specific endonuclease recognition sequences interspersed at regular intervals dependent upon nucleosome structure. These interspersed short repeated sequences could mediate unequal crossovers, resulting in quantitative variability of constitutive heterochromatin and satellite DNA. De novo variations of constitutive heterochromatin may be useful as markers of exposure to mutagens and/or carcinogens.     

Y-chromosome length heteromorphisms in Delhi infants

One hundred and seventy normal male infants from Delhi were studied using the CBG technique to estimate Y-chromosome length heteromorphisms. The median class in Y/F [Y/F = total length of the Y chromosome/average total length of the F group chromosomes (19 and 20)] distribution was 0.75-0.79. The Y/F index in infants varied from 0.60 to 1.16 with a mean of 0.81 and a standard deviation of 0.09. A high incidence for very small (53.5 percent) and small (41.2 percent) categories of Y-chromosome length heteromorphisms was observed. Data were compared with other available reports; also possible mechanisms of the Y-chromosome length heteromorphisms and their role in ethnic/racial variation as well as in developmental disturbances are discussed. It is suggested there may be a need to redefine the long and short Y chromosome in a given population while studying different clinical disorders.     

Tetraploid partial hydatidiform moles: two cases with a triple paternal contribution and a 92,XXXY karyotype

Summary In the course of a systematic study of cytogenetics, morphology, and clinical follow-up of hydatidiform moles we encountered two unusual cases of partial hydatidiform moles each with a 92,XXXY karyotype. Previously reported cases of tetraploidy, of 92,XXXX or 92,XXXY karyotype, resulted from a failure of the first mitotic division of a normal zygote. This is to our knowledge the first report of tetraploidy with XXXY sex chromosomes. Study of chromosomal heteromorphisms, isozymes, and restriction fragment length polymorphisms reveal that both present cases resulted from a combination of a haploid ovum with three haploid sets of paternal chromosomes either by the mechanism of trispermy (involving three separate haploid spermatozoa) or through dispermy (involving one haploid and one diploid sperm). Both cases resembled closely partial moles in their morphology; one gave a highly typical clinical picture while the other was recognized at an early voluntary abortion. Partial moles are ordinarily triploids of nearly always diandric constitution that evince focal villous swelling with cistern formation and focal trophoblastic hyperplasia. The findings here presented point to an association of molar phenotype with an excess of paternal over maternal haploid sets.     

Sex chromosomal dimorphisms narrated by X-chromosome translocation in a spiny frog (<Emphasis Type="Italic">Quasipaa boulengeri</Emphasis>)

Background

In the general model of sex chromosome evolution for diploid dioecious organisms, the Y (or W) chromosome is derived, while the homogametic sex presumably represents the ancestral condition. However, in the frog species Quasipaa boulengeri, heteromorphisms caused by a translocation between chromosomes 1 and 6 are not related to sex, because the same heteromorphic chromosomes are found both in males and females at the cytological level. To confirm whether those heteromorphisms are unrelated to sex, a sex-linked locus was mapped at the chromosomal level and sequenced to identify any haplotype difference between sexes.

Results

Chromosome 1 was assigned to the sex chromosome pair by mapping the sex-linked locus. X-chromosome translocation was demonstrated and confirmed by the karyotypes of the progeny. Translocation heteromorphisms were involved in normal and translocated X chromosomes in the rearranged populations. Based on phylogenetic inference using both male and female sex-linked haplotypes, recombination was suppressed not only between the Y and normal X chromosomes, respectively the Y and translocated X chromosomes, but also between the normal and translocated X chromosomes. Both males and females shared not only the same translocation heteromorphisms but also the X chromosomal dimorphisms in this frog.

Conclusions

The reverse of the typical situation, in which the X is derived and the Y has remained unchanged, is known to be very rare. In the present study, X-chromosome translocation has been known to cause sex chromosomal dimorphisms. The X chromosome has gone processes of genetic differentiation and/or structural changes by chance, which may facilitate sex chromosome differentiation. These sex chromosomal dimorphisms presenting in both sexes may represent the early stages of sex chromosome differentiation and aid in understanding sex chromosome evolution.

     

Optimising human chromosome separation for the production of chromosome-specific DNA libraries by flow sorting

Summary A number of cell lines, some containing chromosomes with distinctive heteromorphisms, have been flow karyotyped using a single laser flow sorter in an attempt to select those suitable for sorting all human chromosomes individually. Using the non-base-specific DNA stain ethidium bromide, chromosomes 3,4,5, and 6 form individual peaks in practically all normal subjects, while the right combination of heteromorphisms enables chromosomes 1, 2, 8, 9, 13, 16, 17, 18, 19, 20, 21, 22, and Y to be sorted separately. Two male cell lines, one containing a duplication and one a deletion of the X, produce flow karyotypes suitable for sorting chromosomes 7 and 8. The use of numerical chromosome abnormalities to enrich the sex chromosomes and the autosomes 18 and 21 is also illustrated. The DNA stain Hoechst 33258 binds preferentially to AT base pairs. Flow karyotypes produced with this fluorochrome separate some chromosomes not well separated with ethidium bromide. Chromosomes 5, 6, 8, 13, 14, 15, 17, and 20, and Y can be sorted individually with Hoechst 33258 with the right combination of heteromorphisms. Using these techniques, all human chromosomes apart from 10, 11, and 12 have been found as individual flow karyotype peaks, suitable for sorting with a high degree of purity.     

Frequencies of centromeric heteromorphisms of human chromosomes 3 and 4 as detected by QFQ technique: can they be identified by RFA technique?

One hundred normal Caucasians were studied by sequential QFQ and RFA banding techniques in order to estimate the type and frequency of heteromorphisms in the centromeric regions of chromosome 3 and 4. Intensity variants were classified into 1 of 5 levels of QFQ banding. QFQ intensity heteromorphisms (greater than or equal to level 3) for chromosomes 3 and 4 were 62 and 15 percent respectively. The interrelationship between QFQ and RFA variants were also examined. When the centromere was brilliant by QFQ, it was found that it was deep red by RFA; when it was pale by QFQ, it was light red by RFA. Neverthless, a blind coded study could not pick up these color variants by RFA. QFQ banding showed variations of the centromeric regions of chromosomes 3 and 4 while RFA banding failed to demonstrate it. It was concluded that QFQ is the most useful technique in detecting the different intensity levels in the centromeric regions of chromsomes 3 and 4.     

Genetics and biology of human ovarian teratomas. I. Cytogenetic analysis and mechanism of origin.

One hundred and two benign, mature ovarian teratomas and two immature, malignant teratomas were karyotyped and scored for centromeric heteromorphisms as part of an ongoing project to determine the chromosomal karyotype and the genetic origin of ovarian teratomas and to assess their utility for gene-centromere mapping. Karyotypic analysis of the benign cases revealed 95 46,XX teratomas and 7 chromosomally abnormal teratomas (47,XXX, 47,XX,+8 [two cases], 47,XX,+15, 48,XX,+7,+12 91,XXXX,-13 [mosaic], 47,XX,-15,+21,+mar). Our study reports on the first cases of tetraploidy and structural rearrangement in benign ovarian teratomas. The two immature cases had modal chromosome numbers of 78 and 49. Centromeric heteromorphisms that were heterozygous in the host were homozygous in 65.2% (n = 58) of the benign teratomas and heterozygous in the remaining 34.8% (n = 31). Chromosome 13 heteromorphisms were the most informative, with 72.7% heterozygosity in hosts. The cytogenetic data indicate that 65% of teratomas are derived from a single germ cell after meiosis I and failure of meiosis II (type II) or endoreduplication of a mature ovum (type III); 35% arise by failure of meiosis I (type I) or mitotic division of premeiotic germ cells (type IV).     

Trisomy 21: Origin of non-disjunction

Summary The Q-band heteromorphisms of chromosome 21 were used in a sample of 48 families with a Down's syndrome child to evaluate the origin of non-disjunction.The parental origin and the meiotic error were determined in 27 families, and in eight families only partial information was obtained. Paternal and maternal origin of non-disjunction was in a 1:3 ratio. Failures were five times more frequent in first than in second meiotic division in both sexes.The mean parental age and environmental factors in relation to the origin of the anomaly are discussed.Our results are compared with those obtained previously in similar studies by other authors.     

Use of restriction fragment length polymorphic probes in the analysis of Down's syndrome trisomy

Summary Restriction fragment length polymorphic probes are being used more frequently in the molecular analysis of Down's syndrome and in the origin of nondisjunction in the syndrome. The type of information gained from RFLPs overlaps but differs from the information from cytogenetic heteromorphisms. From the allele frequencies of commonly available probes we have derived the expected frequencies of all matings in the population. Each mating has been defined and partitioned to show the genotypes and phenotypes expected, with numerical values based on studies with heteromorphisms. From this we show how the various phenotypes can be used to calculate the origin of nondisjunctions and their expected frequencies. Further, an alternative method is outlined for mapping the distance between a probe and its centromere based on the distortion, caused by crossing-over, of the expected 1st to 2nd division nondisjunction ratio. Finally, we discuss prospects for various uses of probes in the analysis of Down's syndrome.     

Application of cloned satellite DNA sequences to molecular-cytogenetic analysis of constitutive heterochromatin heteromorphisms in man

Summary The cloned alpha-satellite DNA sequences were used to evaluate the specificity and possible variability of repetitive DNA in constitutive heterochromatin of human chromosomes. Five probes with high specificity to individual chromosomes (chromosomes 3, 11, 17, 18, and X) were in situ hybridized to metaphase chromosomes of different individuals. The stable position of alpha-satellite DNA sequences in heterochromatic regions of particular chromosomes was found. Therefore, the chromosome-specific alpha-satellite DNA sequences may be used as molecular markers for heterochromatic regions of certain human chromosomes. The homologous chromosomes of many individuals were characterized by cytologically visible heteromorphisms of hybridization intensity with chromosome-specific alpha-satellite DNA sequences. A special analysis of hybridization between homologues with morphological differences provided the evidence for a high resolution power of the in situ hybridization technique for evaluation of chromosome heteromorphisms. The approaches for detection of heteromorphisms in cases without morphological differences between homologues are discussed. The results obtained indicate that constitutive heterochromatin of human chromosomes has a variable amount of alphasatellite DNA sequences. In situ hybridization of cloned satellite DNA sequences may be used as a new general approach to analysis of chromosome heteromorphisms in man.