Characterization and evolution of a single-copy sequence from the human Y chromosome

Molecular features of the TSPY gene of gibbons and Old World monkeys

Restriction pattern, chromosome localization and the sequence of the testis-specific gene, TSPY, were investigated in the white-handed gibbon, agile gibbon, siamang, hamadryas baboon and Japanese monkey. Southern blot analysis showed the TSPY gene to be male specific in the primates used and disclosed variability of restriction pattern in gibbons. Fluorescence in situ hybridization demonstrated that the probe ppTSPY2372, biotinylated using polymerase chain reaction, is located as a slight signal in the proximal long arm of the Y chromosome of the white-handed gibbon, hamadryas baboon and Japanese monkey and in the middle long arm of the Y chromosome of the siamang, while a faint signal and an intense signal were detected in the proximal long arm of the Y chromosome of the aglle gibbon. These findings allow us to speculate that the gibbons might have evolved some structural differentiation in the TSPY gene. The first introns of the TSPY genes were sequenced and compared. One hundred thirty-seven of 606 sites were found to be variable, and 10 deletions/insertions were noted among these gibbons, two species of Old World monkeys and human. Sequence similarity ranged from 81.7% between humans and hamadryas baboons to 98.7% between Japanese monkeys and hamadryas baboons. These sequences may be of great use in future studies for resolving the phylogeny of gibbons and Old World monkeys.

Mapping of human non-muscle type cofilin (CFL1) to chromosome 11q13 and muscle-type cofilin (CFL2) to chromosome 14

Cofilin is a widely-distributed, intracellular, actin binding protein which is involved in the translocation of actin-cofilin complex from cytoplasm to nucleus. We have cloned a non-muscle-type cofilin (CFL1) from a human promyelocytic cDNA library and mapped this to human chromosome 11 by PCR amplification of 3' untranslated sequence in a panel of rodent-human somatic cell hybrids, and to the interval 11q12-q13.2 in a chromosome 11 somatic cell hybrid mapping panel. Confirmation of regional localisation to 11q13 has been obtained by fluorescent in situ hybridisation of genomic cosmid clones, by demonstration of the presence of both SEA (the human homologue of avian retrovirus proviral tyrosine kinase, 11q13) and CFL1 in some of these clones and by close linkage of CFL1 to SEA in a panel of high-dose irradiation hybrids. We have identified human muscle-type cofilin sequences by comparison of human expressed sequence tags with M-type cofilins of other species and we have mapped the human M-type cofilin, CFL2, to chromosome 14.

A human parthenogenetic chimaera

In mice, parthenogenetic embryos die at the early postimplantation stage as a result of developmental requirements for paternally imprinted genes, particularly for formation of extraembryonic tissues. Chimaeric parthenogenetic<==>normal mice are viable, however, due to non-random differences in distribution of their two cell types. Species differences in imprinting patterns in embryo and extra-embryonic tissues mean that there are uncertainties in extrapolating these experimental studies to humans. Here, however, we demonstrate that parthenogenetic chimaerism can indeed result in viable human offspring, and suggest possible mechanisms of origin for this presumably rare event.

Conservation of human Y chromosome sequences among male great apes: implications for the evolution of Y chromosomes

Nine newly described single-copy and low-copy-number genomic DNA sequences isolated from a flow-sorted human Y chromosome library were mapped to regions of the human Y chromosome and were hybridized to Southern blots of male and female great ape genomic DNAs (Gorilla gorilla, Pan troglodytes, Pongo pygmaeus). Eight of the nine sequences mapped to the euchromatic Y long arm (Yq) in humans, and the ninth mapped to the short arm or pericentromeric region. All nine of the newly identified sequences and two additional human Yq sequences hybridized to restriction fragments in male but not female genomic DNA from the great apes, indicating Y chromosome localization. Seven of these 11 human Yq sequences hybridized to similarly-sized restriction endonuclease fragments in all the great ape species analyzed. The five human sequences that mapped to the most distal subregion of Yq (deletion of which region is associated with spermatogenic failure in humans) were hybridized to Southern blots generated by pulsed-field gel electrophoresis. These sequences define a region of approximately 1 Mb on human Yq in which HpaII tiny fragment (HTF) islands appear to be absent. The conservation of these human Yq sequences on great ape Y chromosomes indicates a greater stability in this region of the Y than has been previously described for most anonymous human Y chromosomal sequences. The stability of these sequences on great ape Y chromosomes seems remarkable given that this region of the Y does not undergo meiotic recombination and the sequences do not appear to encode genes for which positive selection might occur.

A human pseudoautosomal gene, ADP/ATP translocase, escapes X-inactivation whereas a homologue on Xq is subject to X-inactivation

We report the cloning of a highly conserved pseudoautosomal gene on the human sex chromosomes. A cDNA clone was selected by crosshybridization with a microdissected clone from the chromosomal subregion Xp22.3. It encodes a previously characterized member of the ADP/ATP translocase family and plays a fundamental role in cellular energy metabolism. This gene, ANT3, is located approximately 1,300 kilobases from the telomere, proximal to the pseudoautosomal gene CSF2RA, and escapes X-inactivation. Interestingly, a homologue of ANT3, ANT2, maps to Xq and is subject to X-inactivation. These genes provide the first evidence of two closely related X-chromosomal genes, which show striking differences in their X-inactivation behaviour.

Structure of the pericentric long arm region of the human Y chromosome

We have analysed the sequence organization of the DNA in the pericentric region of the long arm of the human Y chromosome. The structures of one cosmid and three yeast artificial chromosome clones were determined. The region consists of a mosaic of the known 5, 48 and 68 base-pair tandemly repeated sequences and at least five novel repeated sequence families. A long range-map of approximately 3.5 x 10(6) base-pairs of genomic DNA was constructed that placed the clones between about 500 x 10(3) and 850 x 10(3) base-pairs from the long arm edge of the centromeric alphoid DNA array.

A human moderately repeated Y-specific DNA sequence is evolutionarily conserved in the Y chromosome of the great apes

Evolutionary conservation of the human-derived moderately repeated Y-specific DNA sequence Y-190 (DYZ5) was investigated in the chimpanzee, orangutan, and gorilla. Southern blot analysis showed the presence of the sequence in the Y chromosome of all great apes. Pulsed-field gel electrophoresis and in situ hybridization revealed that the repeat is organized in one major block and confined to a small region of the Y chromosome of the three species. DYZ5 was assigned to the proximal short arm of the Y chromosome of the chimpanzee and orangutan and to the long arm of the Y chromosome of the gorilla. In light of its evolutionary conservation, DYZ5 may have an as yet undetermined structural function in the Y chromosome.

D12S56: a highly polymorphic locus on human chromosome 12q14

A CA repeat, subcloned from a cosmid, has been assigned to chromosome 12 by use of a panel of somatic cell hybrids. The assignment was confirmed by fluorescent in situ hybridization and the site further localized to 12q14. The repeat is highly polymorphic and should be useful for genetic mapping.

Molecular cloning and mapping of 10 new probes on the human Y chromosome

We have developed a novel positive cloning vector whose use precludes the cloning of any fragments less than 0.8 kb as well as 3.4-kb EcoRI fragments of DYZ1, the largest repeating-DNA family on the long arm of the human Y chromosome. Using this vector, we subcloned inserts of a Y-chromosome-specific phage library constructed from EcoRI-digested flow-sorted Y-chromosome DNA. Ten novel Y-specific fragments were obtained. Their localization on the Y chromosome was determined by deletion mapping using clinical samples with structurally abnormal Y chromosomes. The long arm of the Y chromosome was divided into 12 segments by the novel probes in combination with established probes. The amelogenin-like sequence, mapped on the long arm in Human Gene Mapping 10, has been mapped on the short arm.

Correlation of the testicular determinant factor sequence zinc finger Y with varying gonadal phenotypes in a series of 13 subjects with gonadal dysgenesis due to Y aneuploidy

Deoxyribonucleic acid samples from a series of 13 subjects with 45,X/46,X,altered Y, and varying gonadal phenotypes (streak-streak, n = 9; streak-testis, n = 2; testis-testis, n = 2) were analyzed for the presence of the candidate testicular determinant factor sequence zinc finger Y. The Y-specific probes Y97 mapped to Y centromere, pDP105 A,B mapped to Yp and distal Yq11, respectively, hybridized with the deoxyribonucleic acid from all the 13 study subjects. The same deoxyribonucleic acid samples were analyzed for the presence of the zinc finger Y sequence. Eleven of the 13 subjects were positive for the zinc finger Y sequence. Four zinc finger Y-positive subjects had unilateral (n = 2) or bilateral (n = 2) testicular differentiation. Among the nine subjects with bilateral streak gonads, seven showed the presence of this sequence. The lack of testicular differentiation in the presence of quantitatively normal or almost normal zinc finger Y bands could not be explained by mosaicism alone. Mutations not detectable by analysis with the method of Southern with pDP1007, may occur in the testicular determinant factor gene vitiating testicular development.

Structure and polymorphism of human telomere-associated DNA

We have analyzed the DNA sequences associated with four different human telomeres. Two are members of distinct repeated sequence families which are located mainly but not exclusively at telomeres. Two are unique in the genome, one deriving from the long arm telomere of chromosome 7 and the other from the pseudoautosomal telomere. One telomere-associated repeated sequence has a polymorphic distribution among the chromosome ends, being present at a different combination of ends in different individuals. These data thus identify a new source of human genetic variation and indicate that the canonical features of the organization of telomere-associated DNA are widely conserved in evolution.

Rapid cloning and characterization of new chromosome 10 DNA markers by Alu element-mediated PCR

Alu element-mediated polymerase chain reaction is a strategy for rapidly cloning and mapping human DNA markers from mixed DNA sources. A novel primer homologous to the 3' end of the human Alu repeat element provides the basis for preferential synthesis of human DNA fragments from human/rodent somatic cell hybrid DNA template. This approach has been used to isolate a series of new markers from chromosome 10. The Alu element-mediated PCR probes were regionally assigned on chromosome 10 by hybridization to Southern blots of Alu PCR-synthesized DNA derived from somatic cell hybrid template DNA. Alu element-mediated PCR is generally applicable and makes possible the analysis of complex genomes with a speed and sensitivity that has not been previously possible.

A gene from the human sex-determining region encodes a protein with homology to a conserved DNA-binding motif

A search of a 35-kilobase region of the human Y chromosome necessary for male sex determination has resulted in the identification of a new gene. This gene is conserved and Y-specific among a wide range of mammals, and encodes a testis-specific transcript. It shares homology with the mating-type protein, Mc, from the fission yeast Schizosaccharomyces pombe and a conserved DNA-binding motif present in the nuclear high-mobility-group proteins HMG1 and HMG2. This gene has been termed SRY (for sex-determining region Y) and proposed to be a candidate for the elusive testis-determining gene, TDF.

Y chromosome DNA haplotyping suggests that most European and Asian men are descended from one of two males

Three hypervariable Y chromosome DNA loci have been analyzed in human males. The haplotypes defined allow paternal lineages to be identified. Most of these lineages fall into two groups. This indicates that the ancestry of a large proportion of the men studied can be traced back to one of two males.

Molecular scanning of Yq11 (interval 6) in men with Sertoli-cell-only syndrome

Data suggesting that probes pDP105/B and 50f2/C,E may identify sequences on distal Yq11 (interval 6) that are critical for spermatogenesis stimulated a study of this region by means of these two probes in azoospermic 46,XY men with biopsy-proved Sertoli-cell-only syndrome. Deoxyribonucleic acid samples from controls and study subjects were digested with the restriction enzymes TaqI, EcoRI, and BamHI. These samples were blotted and hybridized with pDP105/B, 50f2/C,E, and two more proximal Yq11 probes 4B-2 and pAS1. The sequence hydridizing to 50f2/C was absent in one study subject. No deletions were detected with pDP105/B and the two more proximal probes.

Use of human alpha-satellite deoxyribonucleic acid to detect Y-specific centromeric sequences

The Y alphoid deoxyribonucleic acid probe Y97 has proved to be specific for the human Y centromere and to define a Y-specific 5.5 kb Eco RI fragment. Three experiments were designed to evaluate the sensitivity and the specificity of this Y alphoid probe Y97. In the first experiment the centromeric Y-specific 5.5 kb Eco RI fragment was clearly seen in the mixture of 0.050 microgram of male DNA with 4.950 micrograms of female DNA (1%). In the second experiment the same dilutional study was applied to the Yq11-related probe 4B-2 for comparison purpose. In the third experiment, hybridization with the Y97 probe was performed on 20 subjects with mosaic cell lines containing a cytogenetically identifiable Y (n = 10) and a cytogenetically unidentifiable minute (n = 10) fragment. Nineteen of the 20 subjects demonstrated the Y-specific 5.5 kb Eco RI hybridization band with the centromeric Y97 probe. These experiments demonstrated the utility of the Y97 probe to consistently identify cytogenetically altered Y chromosome fragments and confirm the mapping of the alphoid repeat sequences to the centromeric region of the Y chromosome.

Structure of a hypervariable tandemly repeated DNA sequence on the short arm of the human Y chromosome

The structure of a repeated DNA sequence located on the short arm of the human Y chromosome is described. Genomic mapping and cloning in lambda or cosmid vectors show that the repeated sequence consists of units 20.3 x 10(3) base-pairs long that contain the three previously described DNA sequences: Y-156, Y-190 and Y-223a. Analysis of male genomic DNA by pulsed-field gel electrophoresis shows that the units are tandemly arranged and are organized into two blocks. The major block is hypervariable in size and alleles in the range approximately 540 x 10(3) to 800 x 10(3) base-pairs were detected. The minor block is not variable in size and is approximately 60 x 10(3) base-pairs long. Analysis of rearranged Y chromosomes shows that both blocks are located on the short arm of the chromosome. Most commonly, the major block is distal to the minor block, but the opposite arrangement is also found.

Use of deoxyribonucleic acid probes to test for Yq11 deletions in males with spermatogenic arrest

A cytogenetically detectable deletion in the area of Yq11 has been demonstrated in some men with spermatogenic arrest, leading to the suggestion that a spermatogenic factor(s) lies within this region. The probe pAS1 detects an argininosuccinate synthetase pseudogene 6 (ASSP6), which has been mapped to Ycen-q11. The 4B-2 (DYS 15) probe detects a single-copy 3.3 kb EcoRI fragment that maps to the proximal portion of the Y long arm located distal to the sequence detected by the pAS1 probe. Deoxyribonucleic acid (DNA) samples from normal males and females and ten males with spermatogenic arrest were digested with the restriction endonuclease EcoRI, electrophoresed on agarose gels, Southern blotted, and hybridized with the pAS1 and 4B-2 probes. All males tested, including the ten azoospermic males with spermatogenic arrest, exhibited 4.3 kb and 3.3 kb male specific fragments with the pAS1 and 4B-2 probes, respectively. From preliminary analyses, the authors conclude that the regions detected by these two probes are not absent in these azoospermic males and that the cause of their spermatogenic arrest may not involve deletion within this region. Molecular defects affecting spermatogenesis may involve loss of sequences at Yq11, which were not tested in the study, or they may derive from heterogenous causes.

Use of single (4B-2) and repetitive copy (pS4) deoxyribonucleic acid (DNA) probes to characterize translocated Y DNA in a pedigree with recurrent abortion

Probes for unique and repetitive copy deoxyribonucleic acid (DNA) are available to detect and characterize Y DNA. The probe pS4 detects repetitive copy DNA mapped to Yq12. The upper limits of the pS4 sequences are defined by the upper limits of C-banding. The probe 4B-2 is a recombinant phage construct developed from a Y library and contains a unique copy 3.3 kb Eco RI fragment mapped to Yq11. A family was ascertained through a pregnant female who had a history of four consecutive abortions and two normal daughters. Cytogenetic analysis revealed the mother and one of her daughters to have a 46,XX,15p+ karyotype. Amniocytes were karyotyped as 46,XY,15p+. Genomic DNA from controls, mother, daughters, and amniocytes was digested with Mbo I and hybridized to 32P-labeled pS4 probe. DNAs from both 46,XX,15p+ females and 46,XY,15p+ amniocytes demonstrated a clear male-specific 2.3 kb band. Digestion of the same genomic DNAs with Eco RI and blot hybridization to 32P-labeled 4B-2 probe revealed the 3.3 kb male-specific band only in the 46,XY,15p+ amniocyte DNA. The additional sequences located on 15p segregating in the female members of this family correspond to Yq12. The effect of this additional DNA on gametogenesis is unknown.

Evolution of four human Y chromosomal unique sequences

Four cloned unique sequences from the human Y chromosome, two of which are found only on the Y chromosome and two of which are on both the X and Y chromosomes, were hybridized to restriction enzyme-treated DNA samples of a male and a female chimpanzee (Pan troglodytes), gorilla (Gorilla gorilla), and pig-tailed macaque (Macaca nemestrina); and a male orangutan (Pongo pygmaeus) and gibbon (Hylobates lar). One of the human Y-specific probes hybridized only to male DNA among the humans and great apes, and thus its Y linkage and sequence similarities are conserved. The other human Y-specific clone hybridized to male and female DNA from the humans, great apes, and gibbon, indicating its presence on the X chromosome or autosomes. Two human sequences present on both the X and Y chromosomes also demonstrated conservation as indicated by hybridization to genomic DNAs of distantly related species and by partial conservation of restriction enzyme sites. Although conservation of Y linkage can only be demonstrated for one of these four sequences, these results suggest that Y-chromosomal unique sequence genes do not diverge markedly more rapidly than unique sequences located on other chromosomes. However, this sequence conservation may in part be due to evolution while part of other chromosomes.

Molecular analysis of integrated human papillomavirus 16 sequences in the cervical cancer cell line SiHa

Human papillomavirus (HPV) 16 is frequently found integrated into cervical cancer cell genomes and these integrations are thought to play a role in tumorigenesis. To investigate the mechanisms of HPV integration and its effect on transcription and chromosomal sequence organization, we have cloned and analyzed the HPV16 integration from the cervical cancer cell line SiHa. Restriction analyses and Southern blotting indicated that approximately 95% of an HPV16 genome was integrated without gross rearrangement. Sequence analysis of the cellular-viral DNA junctions revealed that integration had occurred within the E2 and E4 ORFs where 251 bp of viral sequence was deleted. One viral terminus occurred within sequences of an Alu repeat and a 4-bp homology was present at the site of recombination. Using unique cellular flanking DNA probes, a 4.8-kb deletion of cellular sequences was detected at the site of viral integration. The chromosomal location of the viral integration and cellular deletion were mapped to chromosome 13 using a rodent X human somatic cell hybrid panel. Northern blot analysis using viral subgenomic and 3' cellular probes revealed transcription from the 3' portion of integrated HPV16 (E6, E7, E1) and flanking cellular sequences. The observation of viral-cell transcripts and chromosomal deletions associated with HPV integration may indicate that such events are part of a multistep mechanism leading to the development of cervical cancer.

Y chromosome--specific DNA sequences in Turner-syndrome mosaicism

Phenotypic females with Y-chromosomal material in their genome have an increased risk for development of gonadal malignancy. The detection and identification of Y-chromosomal material in these cases can be of critical importance for medical management. Chromosome analysis in four patients with Turner syndrome revealed the characteristic 45,X chromosome complement together with a second cell population containing a small marker chromosome (46,X, + mar). Molecular-hybridization analyses utilizing cloned, Y chromosome-specific DNA sequences were performed to determine whether Y-chromosomal material was present in each patient. Three cases contained some Y chromosome-specific sequences, whereas one case was negative with all four probes that we used. These results were compared with detailed cytogenetic studies--including G-, Q-, and G-11-banding--of the marker chromosomes. In one case in which Y chromosome-specific DNA sequences were demonstrated, the marker chromosome was G-11 negative. These results demonstrate that cytogenetic analysis alone can lead to misidentification of some Y chromosome-derived markers. The combination of cytogenetic and molecular analyses permits a more accurate characterization of anomalous Y chromosomes and in turn provides additional information that can be crucial to the correct medical management of Turner-syndrome patients.

Structure of the major block of alphoid satellite DNA on the human Y chromosome

Alphoid DNA is a family of tandemly repeated simple sequences found mainly at the centromeres of the chromosomes of many primates. This paper describes the structure of the alphoid DNA at the centromere of the human Y chromosome. We have used pulsedfield gradient gel electrophoresis, cosmid cloning and DNA sequencing to determine the organization of the alphoid DNA on each of the Y chromosomes present in two somatic cell hybrids. In each case there is a single major block of alphoid DNA. This is approximately 470,000 bases (475 kb) long on one chromosome and approximately 575 kb long on the other. Apart from the size difference, the structures of the two blocks and the surrounding sequences are very similar. However, one restriction enzyme, AvaII, detects two clusters of sites within one block but does not cleave the other. The alphoid DNA within each block is organized into tandemly repeating units, most of which are about 5.7 kb long. A few variant units present on one chromosome are about 6.0 kb long. These variants, like the AvaII site variants, are clustered. The 5.7 kb and 6.0 kb units themselves consist of tandemly repeating 170 base-pair subunits. The 6.0 kb unit has two more of these subunits than the 5.7 kb unit. Our results provide a basis for further structural analysis of the human Y chromosome centromeric region, and suggest that long-range structural polymorphisms of tandemly repeated sequence families may be frequent.

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.

Human papillomavirus infection of the cervix detected by cervicovaginal lavage and molecular hybridization: correlation with biopsy results and Papanicolaou smear

Human papillomaviruses have previously been identified by molecular hybridization in the majority of dysplastic and cancerous lesions of the cervix. Since human papillomavirus types 16 and 18 have been strongly associated with cervical cancer, the identification of patients infected with these specific human papillomavirus types may provide useful prognostic information. We have developed a painless, noninvasive cervicovaginal lavage technique to collect exfoliated cervicovaginal cells, which can be reliably analyzed for the presence of human papillomavirus deoxyribonucleic acid by Southern blot analysis with the use of deoxyribonucleic acid cloned from human papillomaviruses 6, 11, 16, and 18. In a prospective study of 60 women referred to a colposcopy clinic for evaluation of abnormal Papanicolaou smears, we have detected human papillomavirus deoxyribonucleic acid in 16 of 17 (94%) women with a Class III (dysplasia) or IV (carcinoma in situ) Papanicolaou smear, five of 11 (45%) women with a Class II (atypical) Papanicolaou smear, and 10 of 34 (29%) women with a normal Papanicolaou smear. Detection of human papillomavirus deoxyribonucleic acid in cervicovaginal cells was indicative of a dysplastic cervical lesion in 19 of 20 (95%) patients irrespective of Papanicolaou smear results. We conclude that human papillomavirus deoxyribonucleic acid analysis in cervicovaginal cells is a sensitive method to detect dysplastic lesions of the cervix and may be useful in identifying patients with specific types of human papillomavirus infection, who are at risk to develop cervical cancer.

Use of two different deoxyribonucleic acid probes to detect Y chromosome deoxyribonucleic acid in subjects with normal and altered Y chromosomes

Four experiments evaluated the sensitivity and specificity of molecular techniques to detect human Y chromosome deoxyribonucleic acid. In experiment I, electrophoretic separation of normal male deoxyribonucleic acid fragments after digestion with endonuclease Hae III revealed two male-specific bands of 3.4 and 2.1 kilobase (kb). These bands were not visible if the fraction of male deoxyribonucleic acid in mixed samples was less than 0.3. In experiment II, by means of a repetitive copy Y deoxyribonucleic acid probe (pS4) mapped to Yq12, a male-specific 2.3 kb band was detectable in mixtures of 2.5 ng of male deoxyribonucleic acid and 997.5 ng of 45,X female deoxyribonucleic acid. In experiment III, hybridization with the pS4 probe was performed on the deoxyribonucleic acid of 20 subjects with a normal or a variant Y chromosome. In experiment IV, deoxyribonucleic acid from the same subjects was hybridized to a single copy probe (4B-2) mapped to the Yq11 region. Deoxyribonucleic acid from category A subjects (n = 8) with cytologically normal Y chromosomes hybridized to both deoxyribonucleic acid probes. Deoxyribonucleic acid from category B subjects (n = 2), including a variant Y chromosome that was negative for Q-banding but positive for C-bands, hybridized with the distal pS4 and proximal 4B-2 probes. Deoxyribonucleic acid from category C subjects (n = 10) with variant Y chromosomes uniformly negative for Q- and C-bands, did not hybridize with the pS4 probe. Deoxyribonucleic acid from three of the 10 category C subjects did hybridize to the more proximal sequence-detecting 4B-2 probe. Deoxyribonucleic acid from the remaining seven subjects in category C did not hybridize with either of the deoxyribonucleic acid probes.

Hypervariable telomeric sequences from the human sex chromosomes are pseudoautosomal

Pairing of human X and Y chromosomes during meiosis initiates within the so-called pairing region at the telomeres or the chromosome short arms. Using DNA from the Y chromosome we found sequence homology in the pairing region of the human X and Y chromosomes. This DNA is telomeric, contains repetitive sequences and is highly polymorphic in the population. The polymorphism has allowed family studies which show the sequences are not inherited as though linked to the sex chromosomes. This 'pseudoautosomal' pattern of inheritance points to an obligate recombination in the pairing region of the sex chromosomes during male meiosis.

Pseudoautosomal DNA sequences in the pairing region of the human sex chromosomes

A DNA probe from a human Y chromosome-derived cosmid detects a single-copy genomic DNA fragment which can appear in different allelic forms shared by both sex chromosomes. Variants at this DNA locus show an autosomal pattern of inheritance, undergo recombination with sexual phenotype and can therefore be described as 'pseudoautosomal'. Another probe from the same cosmid detects a sequence repeated 15-20 times per haploid genome. These repeats also appear pseudoautosomal and map exclusively to the short-arm terminal region of each sex chromosome.