Structure and function of Y chromosomal DNA. II. Analysis of lampbrush loop associated transcripts in nuclei of primary spermatocytes of Drosophila hydei by in situ hybridization using asymmetric RNA probes of four different families of repetitive DNA

pSP64/65 subclones of four different families of repetitive sequences on the Y chromosome of Drosophila hydei were used for in vitro synthesis of labelled RNA. Pairs of RNA probes of opposite strand polarity were employed to analyse RNAs transcribed on, or associated with, various Y chromosomal lampbrush loops in nuclei of primary spermatocytes of D. hydei. The results of RNA filter analysis and in situ hybridization experiments can be generalized as follows: (1) Y-specific transcripts are heterogeneous in length and are synthesized on lampbrush loops. (2) Transcription of tandemly repeated sequences is usually strand specific. (3) Members of the same sequence family can be found in transcripts from different lampbrush loops. (4) Transcripts not coded by the Y chromosome are accumulated on different subregions of Y chromosomal lampbrush loops.

Structure and function of Y chromosomal DNA. I. Sequence organization and localization of four families of repetitive DNA on the Y chromosome of Drosophila hydei

The sequence organization of four different families of Y chromosomal repetitive DNA is characterized at three levels of spatial extension along the Y chromosome of Drosophila hydei. At the lowest level of resolution, DNA blot analysis of Y chromosomal fragments of different lengths and in situ hybridization experiments on metaphase chromosomes demonstrate the clustering of each particular sequence family within one defined region of the chromosome. At a higher level of resolution, family specific repeats can be detected within these clusters by crosshybridization within 10-20 kb long continuous stretches of cloned DNA in EMBL3 phages. At the highest level of resolution, detailed sequence analysis of representative subclones about 1 kb in length reveals a satellite-like head to tail arrangement of family specific degenerated subrepeats as the building scheme common to all four families. Our results provide the first comparative sequence analysis of three novel families of repetitive DNA on the long arm of the Y chromosome of D. hydei. Additional data are presented which support the existence of two related subfamilies of repetitive DNA on the short arm of the Y chromosome.

Homoeologic aberrations in human and chimpanzee Y chromosomes: inverted and satellited Y chromosomes

An inverted and a satellited Y chromosome detected in peripheral blood lymphocytes of a chimpanzee and a pygmy chimpanzee, respectively, were characterized cytogenetically by various banding techniques. A detailed comparison with an inverted and a satellited Y chromosome in man suggested that the corresponding aberrations were homoeologic.

Dicentric Y chromosome and mixed dysgenesis

We report 4 cases of mixed gonadal dysgenesis with a karyotype containing a dicentric Y chromosome. All cases were mosaic with 45X and 46X, dic(Y) cell lines. Of the patients 1 had ambiguous genitalia and some features of Turner's syndrome, 2 had classical features of Turner's syndrome with normal female external genitalia and 1 had no features of Turner's syndrome but he presented with penoscrotal hypospadias, inguinal hernia and cryptorchidism. Female gender assignment and early total gonadectomy should be considered when a dicentric Y chromosome is present in cases of mixed gonadal dysgenesis.

The p12f2/TaqI Y-specific polymorphism in three groups of Italians and in a sample of Senegalese

The TaqI/p12f2 Y-specific RFLP was studied in 258 Italians (69 from North, 74 from Centre-South and 115 from Southern Sardinia) and in 65 Senegalese. The two allelic fragments of 10 and 8 kb characterizing this polymorphism were both found in the Italians but only the 10 kb band was found among the Senegalese. The observed frequency of the 8 kb allele was 32.4% in Central-Southern Italians, 17.4% in Northern Italians and 13.0% in Southern Sardinians. The last figure is significantly lower than that (34.3%) previously reported for a smaller sample of the same population.

Study of human sperm chromosomes by sequential transmission and scanning electron microscopy

We describe a method of observing human sperm metaphases by sequential transmission and scanning electron microscopy. This permits the analysis of ultrastructural aspects of sperm chromosomes and allows the relationship between ultrastructure, heterochromatin condensation, and the behaviour and staining properties of sperm chromosomes and heterochromatic regions to be determined.

Mapping the testis determinants by an analysis of Y-specific sequences in males with apparent XX and XO karyotypes and females with XY karyotypes

A number of patients with paradoxical sex chromosome complements (so-called XY females, XX and XO males) have been investigated with a series of 19 Yp and 4 Yq DNA probes to establish which region of the Y is essential for male sexual differentiation. Of the 23 XX males, 18 possessed one or more Yp probe sequences with only 5 lacking such sequences. Of 9 XY females examined, only one showed evidence of a deletion in Yp occurring either as a result of X-Y interchange or interstitial deletion. This suggests that the majority of XY females are not commonly deleted for those Y sequences which are found to be transferred to the X in XX males. The DNA of two XO males both contained different portions of the Y. From a comparison of the patterns of Yp sequences in these patients, it has been possible to elaborate a model of Yp in terms of the order of probe sequences and to suggest a location for the testis determining region in distal Yp.

Cytological evidence that the Sxr fragment of XY,Sxr mice pairs homologously at meiotic prophase with the proximal testis-determining region

Self-pairing of the Y chromosome at prophase of meiosis in XY,Sxr male mice appears to take place in many cells to the exclusion of pairing between the Y and the X. This phenomenon offers an explanation for the high level of X-Y separation seen in these males at prophase of meiosis, additional separations being evident, however, when metaphase I (MI) cells are examined. A minority of prophase cells show the Y paired both autologously and with a sub-terminal region of the X which could be the normal pairing region. The balloon-like configurations observed when self-pairing occurs suggest that the distal Sxr fragment is inverted on the Y chromosome of Sxr carrier males in relation to the normal proximal testis-determining (Td)-containing region.

Immunocytochemical labelling of the kinetochore of human synaptonemal complexes, and the extent of pairing of the X and Y chromosomes

An immunocytochemical method was used to label the kinetochores on human synaptonemal complexes. Synaptonemal complex spreads were labelled with autoimmune CREST serum, followed by a second antibody labelled with colloidal gold, and examined by electron microscopy. Clusters of gold particles were found at discrete sites which were identified as kinetochores on the autosomal synaptonemal complexes, as well as on the XY pair. This method was used to investigate the extent of pairing of the human X and Y chromosomes at pachytene. Our observations confirm earlier work, based purely on measurements, that the pairing of the sex chromosomes sometimes extends beyond the centromere of the Y chromosome into the long arm. At the same time we showed that the centromeric indices of the X and Y at pachytene are highly variable, so that measurements alone are not sufficient to estimate the degree of pairing of the sex chromosomes.

[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.

Y-derived sequences detected in a 45,X male by in situ hybridization

A two-month-old boy with normal genitalia and descended testes was referred for a suspected hematological disorder. Cytogenetic analysis showed a 45,X chromosome constitution. In situ hybridization with the Y-derived probe 50f (provided by Professor Marc Fellous) was performed utilizing metaphase chromosomes to determine whether Y material could be detected. A significant amount of label (17 of 150 cells) was found on chromosome 5p suggesting a 5;Y translocation. This translocation was verified by high-resolution G-banded and G-11-stained chromosomes.

Visualization of pig sperm chromosomes by in-vitro penetration of zona-free hamster ova

Zona-free hamster eggs were penetrated by pig spermatozoa capacitated using bovine follicular fluid and Percoll gradients. A mean penetration rate of 80.1% was obtained from 5 ejaculates from 2 boars. Penetrated eggs were cultured and analysable metaphase chromosome spreads were obtained from 16.8%. The analysis of 20 pig sperm complements indicated that 9 were 19, Y, 10 were 19, X and 1 appeared to have an XY sex chromosome constitution.

De novo X;Y translocation associated with imperforate anus and retinal pigmentary abnormalities

Cytogenetically detectable translocations of Y chromosome material onto the distal short arm of an X chromosome are rare and result in a variable and poorly defined phenotype of short stature and short limbs occasionally associated with mental retardation. We report on a patient with a de novo 46,X,t(X;Y)(p22;q11) chromosome constitution who has additional features not previously described with this chromosome abnormality, including abnormal retinal pigmentation, imperforate anus, and hydronephrosis. Our patient extends the phenotype associated with X;Y translocations, raising new considerations for the clinical management and genetic counseling of such patients and their families.

Nonhomologous synapsis of the XY during early pachynema in In(X)1H male mice

It has been previously supposed that meiotic synapsis is restricted to homology during early, but not late pachynema. The synaptic behavior of an inverted X chromosome, In(X)1H as reflected in the synaptonemal complexes of the sex chromosomes has been examined in microspread spermatocytes by electron microscopy and evidence of extensive nonhomologous synapsis between the X and Y during early pachynema has been obtained.

[Sexual ambiguity and a non-fluorescent Y chromosome]

The personal experience in three patients with ambiguous external genitalia and 45,X/46,XYnf karyotype is reported. The different clinical and cytogenetic aspects of this entity are described and discussed.

Separation of the genetic loci for the H-Y antigen and for testis determination on human Y chromosome

The mammalian Y chromosome encodes a testis-determining factor (termed TDF in the human), a master regulator of sex differentiation. Embryos with a Y chromosome develop testes and become males whereas embryos lacking a Y chromosome develop ovaries and become females. Expression of H-Y, a minor histocompatibility antigen, may also be controlled by a gene on the Y chromosome, and it has been proposed that this antigen is the testis-determining factor. We have tested the postulated identity of H-Y and TDF in the human. H-Y typing with T cells was carried out on a series of sex-reversed humans (XX males and XY females), each shown by DNA hybridization to carry part but not all of the Y chromosome. This deletion analysis maps the gene for H-Y to the long arm or centromeric region of the human Y chromosome, far from the TDF locus, which maps to the distal short arm.

Localisation of Y chromosome sequences in normal and 'XX' males

Three unique sequences derived from the Y chromosome have been mapped within the human genome. A Y specific sequence DYS20 is localised to Yq11.2. DXYS25 and DXYS27 are both X-Y homologous sequences which map to the Y short arm and to Xq21. DXYS25 maps more distally than DXYS27, on the Y short arm and on the X long arm. Y specific restriction fragments for these two sequences are shown to be present in the genome of two XX males, and an aberrant signal for DXYS25 is demonstrated at the tip of an X chromosome short arm in one XX male by in situ hybridisation. The implications of these findings for the location of the testis determining factor are discussed.

A myelodysplastic syndrome with marrow eosinophilia terminating in acute nonlymphocytic leukemia, associated with an abnormal chromosome 16

A patient presented with a myelodysplastic syndrome and bone marrow eosinophilia that evolved six months later into an acute nonlymphocytic leukemia (ANLL). Cytogenetic analyses of the bone marrow revealed 86% of the metaphases with 45,X-Y,inv(16)(p13;q22),t(11;17) (q11;q25),del(21)(q13) and 14% of the metaphases with the same abnormalities but with a Y chromosome. The association of ANLL, bone marrow eosinophilia, and abnormal chromosome 16 has previously been reported and has been suggested to have a favorable prognosis. Our patient is unique in that ANLL was preceded by a preleukemic phase associated with bone marrow eosinophilia. When complete remission was achieved, the bone marrow cytogenetics returned to normal, and the eosinophilia disappeared.

Size variation in kinetochores of human chromosomes

Aneuploidy, the loss or gain of chromosomes from cells, is likely in many cases to involve the kinetochore, the site of attachment of spindle microtubules. We analyzed human fibroblast cells with antikinetochore-antibody indirect immunofluorescence, and noted an apparent heterogeneity in the sizes of kinetochores among different chromosomes. The Y chromosome in particular always showed minute kinetochores, an observation which was quantified and substantiated using computer-assisted image analysis. This finding, combined with literature reports about in vivo and in vitro involvement of the Y chromosome in aneuploidy, was used to frame a novel hypothesis about the generation of chromosome imbalance.

The chromosomes of Micromys minutus (Rodentia, Murinae). II. Pairing pattern of X and Y chromosomes in meiotic prophase

Both light and electron microscopy were used to study the pairing behavior of the sex chromosomes of the harvest mouse, Micromys minutus, in surface-spread pachytene spermatocytes. The XY pairing pattern is very exceptional in that the site of synaptic initiation is located interstitially in the short arms of the X and the Y, next to their centromeric regions. From this tiny euchromatic site, synapsis proceeds unidirectionally along the homologous heterochromatic short arms of the X and the Y toward the ends of the chromosomes. After pairing of the short arm is concluded, synapsis begins between the nonhomologous long arms of the X and the Y in the immediate vicinity of the centromeres and progresses unidirectionally toward the end of the long arm of the Y. A synaptic complex develops between the constitutive heterochromatin of the long arm of the Y and the euchromatin of the long arm of the X. Analysis of C-banded and distamycin A/DAPI-stained diakineses revealed a trefoil-like XY bivalent, which was interpreted to be the result of an interstitial chiasma occurring in the paired short arms of the X and the Y. A conspicuous, electron-dense body, about 1 micron in diameter, was found closely associated with the centromeres of the X and the Y in numerous pachytene spermatocytes. A review of the literature showed that comparable XY-associated bodies have been found in only eight other mammals to date.

Chromosomal polymorphisms of 1, 9, 16, and Y in 4 major ethnic groups: a large prenatal study

Using trypsin Giemsa banding (GTG), major polymorphisms of the constitutive heterochromatin regions of chromosome 1, 9, 16, and Y were recorded in a New York City population. Polymorphisms were recorded from amniotic fluid specimens received from 6,250 patients from 4 major population groups, ie, White (European)-2,334 cases, American Black-1,795 cases, Hispanic descent-1,737 cases, and Asian (Oriental and Indian)-384 cases. The major chromosomal polymorphisms were classified as follows: obvious pericentric inversion of the constitutive heterochromatin of the long arm of the chromosome (inv qh); significantly enlarged heterochromatic region of the long arm (qh + is greater than, or equal to, twice the size of the short arm of chromosome 16 [16p]); very small or deficient heterochromatic region in the long arm (qh-); large Y (Yq + greater than size of chromosome 18), small Y (Yq- less than size of a G-group chromosome), and pericentric inversion of Y. Our prenatal study confirmed that the incidence of specific chromosomal variants is different in each population group. The most striking examples of this are the pericentric inversion of chromosome 9 and the different polymorphisms of the Y chromosome. The incidence of inv (9) is highest in the Black population (3.57%); slightly above average in Hispanics (2.42%); and relatively low in Whites (0.73%) and Asians (0.26%). The Y appears to be more variable in Asian (3.37%) and Hispanic (1.82%) than in White or Black groups. The 9qh+ is seen more frequently than 1qh+, or 16qh+. Inv (1), 9qh-, and 16qh- are rare. There were no cases of either 1qh- or inv (16).(ABSTRACT TRUNCATED AT 250 WORDS)

Evolution of Y chromosomal lampbrush loop DNA sequences of Drosophila

The evolutionary conservation of Y chromosomal DNA sequences of Drosophila hydei in different species of the genus Drosophila was studied by in situ hybridization and on genomic DNA blots of restriction enzyme digested DNA. We demonstrated that Y specific DNA sequences, which form major parts of lampbrush loops related to the male fertility genes, are only retained in a few closely related species during evolution. Other Y chromosomal DNA sequences, also present in lampbrush loops but with homology to autosomal and X chromosomal locations, were found in distant species. We propose a model for the evolution of the Y chromosomal lampbrush loops.

Inverted Y chromosome polymorphism in the Gujerati Muslim Indian population of South Africa

An inverted Y chromosome has been found at a very high frequency in a Muslim Indian community living in the Johannesburg-Witwatersrand area of the Transvaal Province of South Africa: 8 of 141 (5.7%) retrospectively identified Indian males had an inv(Y)(p11.2q11.23) and all were of the Muslim faith. The inversion was found in 22 of 72 (30.5%) prospectively studied normal Muslim Indian males. All the carriers of the inversion were Gujarati-speakers whose families migrated to the Transvaal from the Gujerat Province of India during the first half of this century. The origins of the ancestors of the individuals with inv(Y) were traced to a small village, Kholvad, near the city of Surat, and some neighbouring villages. The polymorphic frequency of the inv(Y) has probably been produced through random genetic drift in a reproductively isolated community, maintained by strict endogamous marriage customs based on religious and linguistic affiliations. There was no indication that the inverted Y was associated with any reproductive disadvantages.

[XX male syndrome: a study model of the genetic determination of the male sex]

Using Y-specific probes, issued from a library of the human Y chromosome, DNA from about 30 XX men has been studied by the Southern technique. Two groups of patients could be distinguished: one with Y genetic material, the second, without Y DNA. Among XX males with Y sequences there was a genetic heterogeneity with a variable amount of Y DNA sequences. These Y DNA sequences come from the short arm of the Y chromosome and are probably translocated to the paternal X. Concerning the other group, in which no Y sequence could be detected, either Y DNA was present but was not detected, or the mechanism of maleness was Y-independent.

Deletion mapping of the testis determining locus with DNA probes in 46,XX males and in 46,XY and 46,X,dic(Y) females

Eleven Y-specific DNA probes hybridizing with DNA from one or more 46,XX males were isolated from a recombinant phage DNA library constructed from flow sorted human Y chromosomes. Two probes hybridized with DNA from nine out of eleven, i.e. greater than 80% of these 46,XX males. The relative frequency of hybridization of the probes in the 46,XX males and in a 46,X,dic(Y) female, together with in situ hybridization data, allowed mapping of the probes on Yp in relation to a putative testis determining locus. Several of those probes were also absent in a 46,XY female, further refining a model for ordering the probes on Yp. The DNA of one XX male hybridized both with probes from Yp and probes from proximal Yq (excluding the pericentral region). This suggests that complex translocations may occur into the DNA of 46,XX males that involve not only parts of Yp but also parts of Yq.

Variable transfer of Y-specific sequences in XX males

A series of twelve XX males and their relatives have been examined by Southern blot analysis with fourteen different Y recombinants. The pattern of Y sequences present shows considerable variation between XX males. Furthermore, on the basis of the terminal transfer model, anomalous patterns of Y sequences are evident in certain XX males in that sequences located as proximal Yp by means of a Y deletion panel are found to be present in the absence of distal sequences. These anomalies can be resolved by proposing that the order of Yp sequences varies in the population in the form of inversion polymorphisms in the Y chromosomes of normal males. Alternatively, it is necessary to invoke multiple recombination events between the X and Y chromosomes to explain the patterns of Y sequences in these XX males. Southern analysis on DNA prepared from flow sorted X chromosomes of XX males indicates that the Y sequences in these patients are linked to X chromosomes.

[Differential condensation of human chromosomes 9 and Y]

Some differences were observed in the mitotic condensation of regions composing human chromosomes 9 and Y: regions 9p, 9h and Y nf are characterized by an intense condensation by the end of the spiralization interval studied (the length of the repair chromosome 3 varying from 5.4 to 2.9 mkm). At the same time, the condensation of regions 9q-h (region 9q without heterochromatic block) is slowing in the initial spiralization interval (the length of chromosome 3 varying from 16.6 to 5.5 mkm). The Yf-block of Y-chromosome is condensing faster than nf-region. The condensation parameters of Q-heterochromatic blocks are most variable while the euchromatic regions are most stable. The dynamics of 9h and of f-block condensation are independent within one karyotype. Based on the data obtained we doubt the correctness of studies on linear dimensions of the constitutive heterochromatin blocks for the evaluation of its quantity in the karyotype. A possible association of differential mitotic condensation with the chromosome segregation disturbances is discussed.

Sex determination from buccal mucosa and hair root by the combined treatment of quinacrine staining and the fluorescent Feulgen reaction using a single specimen

In order to determine sex using a single specimen, buccal mucosa and hair roots obtained from male and female individuals were used. The specimens were first stained with quinacrine for the detection of the Y-chromatin, and subsequently were stained by the fluorescent Feulgen reaction using acriflavine for the detection of the X-chromatin. In the male specimens, the frequency of fluorescent spots of quinacrine-positive bodies was high, whereas that of acriflavine-positive spots was low. On the other hand, in the female specimens, the frequency of quinacrine-positive spots was very low, while that of the acriflavine-positive spots was high. These specimens were air-dried and were allowed to stand at room temperature for periodical observations. The result was that sex difference was distinguishable for 4 months by the combined treatment method.

Chromosomal localization of genes by scanning electron microscopy using in situ hybridization with biotinylated probes: Y chromosome repetitive sequences

The feasibility of using scanning electron microscopy (SEM) to identify the position of specific DNA sequences was examined using a Y chromosome 'specific' probe (pHY2.1). Tests were carried out on chromosome spreads hybridized in situ with biotinylated pHY2.1. Chromosomal sites of hybridization of the probe were localized by an indirect immunohistochemical procedure which resulted in a gold product which could be amplified by silver precipitation. In the SEM, the specific location of the probe was easily identified due to the enhanced signal produced by the gold-silver complex. The probe was localized both on the long arm of the Y chromosome and within interphase nuclei. It was found that SEM was more sensitive than light microscopy since the probe could be identified without silver amplification. With refinements to the technique, SEM could provide a useful method for high resolution localizing of unique DNA sequences (i.e. single copy genes).

[Roberts' syndrome. Review of the literature and presentation of 2 clinical cases]

Two new cases of Robert's Syndrome (R.S.) are presented. Both clinic and cytogenetic aspects of R.S. are rapidly reviewed. The significance of cytogenetic findings in R.S. is discussed.

Homozygosity for a Y/22 chromosome translocation: t(Y;22) (q12;p12/13)

A newborn girl, homozygous for a balanced Y/22 chromosome translocation is described. This unique karyotype was detected during prenatal chromosome studies in the first pregnancy of a 26-year-old woman. Amniocentesis was performed because of clinical evaluation of severe fetal growth retardation in the 28th week of gestation. The cytogenetic results were confirmed using a lymphocyte culture after birth in the 30th week. Subsequent chromosome studies of the parents were hampered by the fact that the pregnancy was thought to be the result of artificial insemination with donorsperm. Nevertheless both, consanguineous, parents were shown to be carriers of the same, singular, chromosome translocation and the spermdonor could be excluded from paternity by bloodgroup- and HLA studies. Distamycin-A-DAPI chromosome staining and DNA studies of the mother were used to confirm the involvement of the Y-chromosome in this translocation. The probanda is developing quite normally at the age of 21 months.

Genetic control of sex-chromosomal univalency in the spermatocytes of C57BL/6J and DBA/2J mice

The genetic control of sex-chromosomal univalency was examined in the primary spermatocytes of the mouse. The C57BL/6J strain expresses 3% X-Y univalency and DBA/2J expresses 37% univalency. The reciprocal F1 and the eight types of reciprocal backcross males were examined. In the C57BL/6J--DBA/2J strain pair, X--Y univalency is controlled by three genetic systems. Autosomal factors of unknown number that are dominant in DBA/2J increase the probability of univalency from 3% in C57BL/6J to 12%. The DBA/2J-Y chromosome, in place of the C57BL/6J-Y chromosome, has an additive effect to increase the probability of univalency from 12 to 37% in the DBA/2J strain. Two X-chromosome factors that differ between C57BL/6J and DBA/2J regulate the probability of univalency. The X-chromosome factors appear to be separated by sufficient distance so that, with the DBA/2J-Y chromosome and dominant DBA/2J autosomal factors, there are two recombinant classes of X--Y univalency at 20 and 60%. The genetic factors in the univalency trait may be involved in the regulation or structure of the terminal attachment sites between the X and Y chromosomes.

The human Y chromosome

Despite its central role in sex determination, genetic analysis of the Y chromosome has been slow. This poor progress has been due to the paucity of available genetic markers. Whereas the X chromosome is known to include at least 100 functional genetic loci, only three or four loci have been ascribed to the Y chromosome and even the existence of several of these loci is controversial. Other factors limiting genetic analysis are the small size of the Y chromosome, which makes cytogenetic definition difficult, and the absence of extensive recombination. Based on cytogenetic observation and speculation, a working model of the Y chromosome has been proposed. In this classical model the Y chromosome is defined into subregions; an X-Y homologous meiotic pairing region encompassing most of the Y chromosome short arm and, perhaps, including a pseudoautosomal region of sex chromosome exchange; a pericentric region containing the sex determining gene or genes; and a long arm heterochromatic genetically inert region. The classical model has been supported by studies on the MIC2 loci, which encode a cell surface antigen defined by the monoclonal antibody 12E7. The X linked locus MIC2X, which escapes X inactivation, maps to the tip of the X chromosome short arm and the homologous locus MIC2Y maps to the Y chromosome short arm; in both cases, these loci are within the proposed meiotic pairing region. MIC2Y is the first biochemically defined, expressed locus to be found on the human Y chromosome. The proposed simplicity of the classical model has been challenged by recent molecular analysis of the Y chromosome. Using cloned probes, several groups have shown that a major part of the Y chromosome short arm is unlikely to be homologous to the X chromosome short arm. A substantial block of sequences of the short arm are homologous to sequences of the X chromosome long arm but well outside the pairing region. In addition, the short arm contains sequences shared with the Y chromosome long arm and sequences shared with autosomes. About two-thirds of XX males contain detectable Y derived sequences. As the amount of Y sequences present varies in different XX males, DNA from these subjects can be used to construct a map of the region around the sex determining gene. Assuming that XX males are usually caused by simple translocation, the sex determining genes cannot be located in the pericentric region. Although conventional genetic analysis of the Y chromosome is difficult, this chromosome is particularly suited to molecular analysis. Paradoxically, the Y chromosome may soon become the best defined human chromosome at the molecular level and may become the model for other chromosomes.

Argentophilic structures of spermatogenesis in the yellow fever mosquito

Application of the silver-staining technique to air-dried chromosome preparations of the yellow fever mosquito, Aedes aegypti, revealed the following: 1) intensely stained pericentromeric regions in all chromosomes including the Y chromosome in spermatogonia, and during the primary and secondary spermatocytes; 2) the presence of prepachytene that were not reported earlier; 3) a nucleolus organizing region that persisted up to the late pachytene stage; and 4) rod or ring-like centrioles in pachytene and diplotene stages. In addition, varying numbers (1-4) of silver-stained, ring-like structures were observed during spermiogenesis. The exact nature and function of these ring-like structures is not understood.

Unequal mitotic sister chromatid exchange and different length of Y chromosomes

There is wide variation in the length of the Y chromosome. In the same individual the length varies continuously and is normally distributed. We describe a boy with borderline mental retardation, gross and fine motor coordination difficulty, muscle rigidity, ptosis, clinodactyly, and a Y chromosome of different lengths in two separate cell populations. The most probable explanation of the cytogenetic finding is a mitotic unequal sister chromatid exchange of the Y chromosome.

The structural basis for C-banding. A scanning electron microscopy study

The same C-banded human polymorphic chromosomes were observed in the light microscope (LM) and then in the scanning electron microscope (SEM) to investigate the structural changes produced by the C-banding technique. C-banded regions, which stained positively in LM, were highly condensed with tightly packed chromatin fibres, resembling non-banded chromosomes. In striking contrast, adjacent non-C-banded regions were represented by loosely arranged fibres, resembling G-banded chromosomes. The significance of these observations in relation to current theories on the effects of C-banding on chromosome structure is discussed.

Molecular evidence for partial inactivation of Y loops in T(X:Y)56 males from D. hydei

Using loop-specific DNA clones, we established that the T(X:Y)56 (Hackstein and Hennig 1982) chromosome, formerly thought to be deleted for the Yshort arm and the associated 'nooses' loops is actually an XYS X YL combination. It carries, adjacent to the translocation junction, the complete and uninterrupted set of the two dysfunctional 'nooses' domains. The morphologically altered and functionally defective loops are transcribed at about 50% of the normal rate. Transcripts in one of the two 'nooses' domains are preferentially underrepresented and their distribution in the spermatocyte nucleus is distorted, presumably as a consequence of a spreading effect. No alteration in transcript size or in the correct strand selection, and no variegation of transcription on the single spermatocyte level, were observed. In another translocation T(X:Y)97, in which 'tubular ribbons' were reported to be inactivated (Hess 1970), complete elimination of DNA sequences is observed. A possible mechanism for the position effect inactivation of Y loops in X:Y translocations is discussed briefly.

High long-standing fertilizing capacity of human sperm isolated for male sex preselection

A method of separating a Y-enriched human sperm population for male sex preselection with a single-column, four-step, four-layer albumin gradient technique is presented. This technique provides an efficient separation of spermatozoa, good Y-enriched sperm motility, and high fertilization capacity of this fraction as tested by the zona-free hamster ova sperm penetration assay.

Preparative dual-beam sorting of the human Y chromosome and in situ hybridization of cloned DNA probes

Bivariate Hoechst/chromomycin flow karyotypes for chromosomes from a Chinese hamster-human hybrid cell line (CH-Y-VII) were established that have retained a human Y chromosome. These bivariate flow karyotypes showed the human Y chromosome to be completely separated from the peaks for the Chinese hamster chromosomes. In preparative dual-beam sorting experiments, 3 X 10(6) chromosomes were sorted from the Y peak into frozen petri dishes. An examination of Q-banded samples of sorted chromosomes revealed that 82% +/- 5% of them were human Y chromosomes. The DNA from the sorted chromosomes (approximately 250 ng) was isolated and used to establish a genomic library (vector lambda gt WES. lambda B). Three clones (YACG 45, 52, 54) of this library containing inserts of repetitive human DNA were used for chromosomal localization by means of in situ hybridization to metaphase spreads of male human lymphocytes and of CH-Y-VII cells. In all three cases, a significant binding to the human Y chromosome was observed. A more detailed study of the chromosomal distribution of sequences homologous to the insert of YACG 45 suggested the existence of minor binding sites on several human autosomes. Southern blot analysis revealed the existence of other human specific sequences without Y chromosome specificity.

Investigation of human chromosome polymorphisms by scanning electron microscopy

Human chromosome polymorphisms were investigated by scanning electron microscopy (SEM). Centromeric heterochromatin was of a constricted morphology. The extent of the C banded region was demarcated by a prominent circumferential groove in G banded chromosomes. Circumferential grooves were observed within the heterochromatin of chromosome 9, and the number of grooves present reflected the size of the region. Three dimensional viewing of satellites and short arms of acrocentric chromosomes, from different angles in the SEM, provided the opportunity for accurate assessment of the size of satellites to be made. Also, small morphological variations were defined in the SEM when definition was uncertain in the light microscope (LM).

[Individual and age-related characteristics of the mitotic condensation of human Y chromosome]

Three types of contraction (steady, speeding and slowing) of fluorescent (f) and nonfluorescent (nf) parts of the human Y chromosome were revealed in the spiralization interval limited by reper chromosome 3 length from 16.6 to 2.9 mkm. On the basis of regression analysis it was shown that in the initial phase of the spiralization interval studied the f-block was condensed more rapidly than the nf-region; then the speed of contraction of the latter exceeded that of the former. A decline of the Y chromosome condensation in relation to ageing was revealed. A possible chromosome segregation disturbance in gametogenesis due to senescent changes of heterochromatic regions is discussed.

[Heterochromatin of the human Y chromosome as an example of selfish DNA]

The nature of human Y-chromosome of Q-positive heterochromatic region is discussed. Both the authors data and those from literature show the existence of human population polymorphism with respect to the appearance of this region which consists of one or several bright fluorescent blocks. Their multiplication results probably from an unequal sister-strand crossing-over. Absence of these blocks has no visible phenotypic effect. Their extra multiplication affects the embryonal and possibly postnatal psychic development. It is supposed that Q-positive heterochromatin is an example of selfish DNA in the human genome.

Suppression of ribosomal RNA genes in Drosophila melanogaster

The rDNA of fiveYchromosome mutants was examined with respect to their insert free (In−) repeat type multiplicity. The In− repeat number of each mutant was correlated with its hemizygousbobbedphenotype and additivity with anXNObobbed(bb) mutant. Four of these mutants showed a direct relationship between their In− frequency, hemizygousbbphenotype and additivity tests. A fifth mutant,bb1–4, had a sufficient number of In− repeats to ensure viability to the late pupal stage and show additivity; however, the In− repeats genetically behaved as a complete rDNA deletion. Possible mechanisms resulting in the suppression of thebb1–4In− repeats are discussed.

A male-specific DNA probe detects heterochromatin sequences in a familial Yq- chromosome

Using a recombinant DNA probe, we have demonstrated the presence of residual 3.4-kilobase (kb) repeat sequences in a family with a Yq- chromosome. The heterochromatin of this Y variant was not readily detectable with conventional chromosome-banding techniques. These data suggest that the breakpoint of the deletion occurs at the heterochromatin region proximal to the euchromatin/heterochromatin junction.