Human Molecular Genetics

Figure 4. The structures present in the chimpanzee, gorilla and orang-utan genomes at positions orthologous the human Xp/Yp telomere junction region. The hatched rectangle represents the SINE sequence, striped horizontal arrows indicate minisatellite repeat, black horizontal arrowheads indicate telomere repeat, crossed horizontal arrows indicate subterminal satellite, the filled vertical arrows on the line between the two orang-utan structures represent points of sequence difference; these include insertion/deletions. Sequence differences between the gorilla 4 and 3 repeat unit alleles are indicated by filled arrows below the gorilla structure. The positions of allele-specific primers are indicated by horizontal arrows.

Gorilla

The `telomere-adjacent' minisatellite is present in the gorilla, with two alleles of three and four repeat units present among six individuals examined. Four of the gorillas were homozygous for the three repeat unit allele and two were heterozygous. A total of 2223 bp of contiguous sequence was obtained from the gorilla allele containing three minisatellite repeats (EMBL accession no. Z96950). Sequence heterogeneity within the minisatellite reveals that the third most distal repeat unit is absent (Fig. 4 ). The sequence analysis defined the block of interstitial telomere-like repeats. It is variable in length, as arrays of nine and 10 telomere-like repeats were present in the individual analysed. The start of the block of telomere-like repeats corresponds to the position -125 from the start of the human telomere (Fig. 3 ). Surprisingly the gorilla telomere-like repeat array and sequences beyond it have strong homology to subtelomeric DNA from human chromosomes 4p, 18p and 4q, (94, 93 and 92% respectively) (20 -22 ). The 18p and 4q sequences contain interstitial telomere repeats in the same position as those in the gorilla Xp/Yp sequence.

DNA sequence from the gorilla allele that contained a four repeat unit minisatellite was also established over 2287 bp (EMBL accession no. Z96951) via allele-specific amplification with primers Gor4A and Gor4B (Fig. 4 ). Comparison of the sequence obtained from the two gorilla alleles (EMBL accession nos Z96950 and Z96951) revealed 11 base substitutional differences between them (sequence divergence of 0.4%). The frequency of base substitutional sequence variation between the two gorilla alleles (1 per 203 bp, see Fig. 4 ) is much lower than observed in the kilobase of sequence adjacent to the human Xp/Yp telomere.

Table 1 . Pairwise comparisons between DNA sequences orthologous to the 2007 bp of DNA immediately adjacent to the human Xp/Yp telomere

Species compared	Sequence compared (bp)	Percentage divergence	Previously published % sequence divergences (difference)
hu/ch	1966	3.5	1.61 (2.2)
hu/gor	1886	4.0	1.72 (2.3)
hu/orL	2563	9.6	3.39 (2.8)
hu/orU	2413	10.4	3.39 (3.1)
ch/gor	1932	4.2	1.84 (2.3)
ch/orL	2556	9.4	3.52 (2.7)
ch/orU	2372	9.8	3.52 (2.8)
gor/orL	2499	8.8	3.47 (2.5)
gor/orU	2225	9.2	3.47 (2.7)
orL/orU	2383	2.0
			Average (2.6)

The sequence differences between the species were distributed across the region, and between the two orang-utan structures. Comparisons were made and divergence estimates obtained using Bestfit (Genetics Computer Group version 6.2). Previously published sequence divergence estimates from the [phi][eta]-globin gene region were included for comparison (5). hu, human haplotype A, ch, chimpanzee, gor, gorilla and orU/orL, orang-utan upper and lower fragments respectively.

Orang-utan

Initial sequence analysis of the orang-utan revealed a large number of differences between orL and orU (5.0 and 5.3 kb fragments). PCR primers (OrangUp and OrangLow, Fig. 4 ) were designed and used in combination with one of the primers TSK8K on the four orang-utan DNAs. The one animal, heterozygous for orL and orU, generated amplification products with both primers. The other three orang-utans only generated PCR products in the presence of the OrangLow primer (data not shown). This suggested that orL and orU contain diverged sequences, and so sequence analysis was carried out on both.

Contiguous sequence data (2846 bp) was obtained from orU (EMBL accession no. Z96952). A novel GC-rich (70%) minisatellite consisting of eight 56 bp repeat units, with sequence variation between the repeats, was identified (Fig. 4 ). Sequences orthologous to the human telomere-adjacent minisatellite and to the SINE were also present in the orU fragment. However, only two minisatellite repeat units were present, and sequence variation suggests that the central two repeat units are absent in the orU fragment. The orU SINE sequence is 280 bp longer than in humans and extends past the position equivalent to the start of the human telomere (Fig. 4 ). Immediately distal to the SINE is an array of at least 31 telomere-like repeats.

A total of 2182 bp of sequence data was obtained from orL (EMBL accession no. Z96953). Surprisingly, the orL allele contains the same 45 bp duplication observed in the chimpanzee sequence (Fig. 4 ). The 56 bp minisatellite repeat sequence detected in the orU allele is present, as an array of 15 repeat units that also showed sequence variation between repeats. Further PCR analysis has shown that the orang-utan-specific minisatellite is variable, with four different length alleles observed among three orang-utans. Sequences similar to the human telomere-adjacent minisatellite are present in orL and, like the orU fragment, the central two repeats are absent. However, the SINE is completely absent in orL and instead an array of telomere-like repeats was identified distal to the minisatellite (Fig. 4 ). These telomere-like repeats consist of diverged repeats often reiterated into a higher order structure such as (TCCGGGTCCGGGTCAGGG)_n in the 39 repeats sequenced. Amplification with a telomere repeat primer in conjunction with a 5' radioactively labelled primer in the minisatellite region (PrimA, Fig. 1 ) revealed a ladder of fragments extending for at least 100 repeat units (data not shown). This confirmed that the smear of products shown in Figure 3 was generated from a long array of telomere-like repeats. Furthermore, preliminary PFG analysis suggested that the long array of telomere-like repeats is located on the terminal restriction fragment in the orang-utan, indicating that the telomere-like repeats in orL represent a diverged region at the proximal end of the orang-utan Xp/Yp telomere.

Comparison of the orU and orL sequences revealed a large number of differences resulting in 2% divergence (Fig. 4 ; Table 1 ). The high level of sequence variation (one every 50 bp) between orU and orL is similar to that observed between haplotypes adjacent to the human Xp/Yp telomere. However, in contrast to the human Xp/Yp haplotypes, there was no significant clustering of sequence polymorphism in the orang-utan (Fig. 4 ). It is noteworthy that the two divergent orang-utan sequences are probably adjacent to the telomere, possibly suggesting that the same underlying forces have been involved in the evolution of these sequences in humans and orang-utans.

Two alternative explanations for the differences between orL and orU can be considered. Firstly that orL and orU represent a polymorphic duplication of the telomere-adjacent DNA. This seems unlikely because there is no evidence of a duplication of the DXYS14-like locus in orang-utans (see Fig. 2 ). In addition, no more than two alleles per individuals have been detected at the orang-utan-specific minisatellite but, if the sequence was duplicated, additional DNA fragments might be detected. Secondly, orL and orU could be derived from different orang-utan subspecies. Two separate subspecies of orang-utan exist in Borneo (Pongo pygmaeus pygmaeus) and north Sumatra (P.pugmaeus abelii). The subspecies are characterised on the basis of morphological, behavioural and cytogenetic differences (23 ,24 ). This categorisation has been supported recently by molecular data, which suggest the two subspecies diverged 1.5-1.7 million years ago (25 ). Since the two orang-utan subspecies can form fertile hybrids (26 ), it remains possible that the heterozygous orang-utan containing orL and orU was the offspring of an inter-subspecies mating. If so, then orL and orU would represent subspecies-specific structures, as for example the pericentric inversion of orang-utan chromosome 2, that has been used for subspecies classification (24 ). At the time that blood samples were collected, the two orang-utan subspecies were not managed separately in captivity, as is now the case, and the subspecies classification of the orang-utans analysed in this study are therefore unknown.

Sequence comparison and ancestral structures

Pairwise comparisons were made between the sequences obtained from the higher primates. Higher levels of sequence divergence were observed compared with other loci (Table 1 ) such that, on average, the between-species divergence is 2.6-fold higher across the subterminal Xp/Yp sequences than at the [psi][eta]-globin pseudogene or other non-coding loci (5 ,27 -29 ).

Sequence variation was identified in the gorilla and orang-utan DNAs, but none of the variant positions were the same as those identified in humans. In order to derive the ancestral state for the human Xp/Yp telomere-adjacent haplotypes identified at the Xp/Yp telomere junction, the sequences of the polymorphic sites that define the human haplotypes were compared in each of the species examined (Table 2 ). In all but three positions, there is complete concordance between the species. Therefore, these polymorphic positions have probably been derived since the divergence of the Pan and Homo lineages. At three positions (-1888, -338 and -146, Table 2 ), the sequence was different between the species. At two of these positions (-338 and -146), the bases found are the same as in the divergent human haplotypes.

DISCUSSION

Here we have described the characterisation of sequences orthologous to the human Xp/Yp telomere from the chimpanzee, gorilla and orang-utan genomes. The sequence divergence between species was higher (2.6×) than that identified in other regions of the genome. There is evidence that gross chromosomal rearrangements, including truncations and exchanges between subterminal sequences of Xp/Yp and autosomes, have occurred, resulting in sequence organisation that is different in each of the four lineages analysed. These data show that a variety of mutational processes have brought about many changes in the Xp/Yp telomeric region over a relatively short period of evolutionary time.

Deriving the ancestral structure

The overall distance between DXYS14 and a point defined by the start of the human telomere was probably 5.0 kb in the common ancestor. The sequences deleted from the human lineage to reduce this distance to 3.6 kb and the sequence inserted into orU to increase it to 5.3 kb have not been identified but must lie between DXYS14 and the start of the region we have sequenced.

The SINE sequence is truncated or absent in each lineage, with the exception of the orang-utan upper allele (orU). Therefore, the common ancestor probably contained a longer SINE sequence. The SINE has since been truncated at a different site in each lineage by different sequences. The subterminal satellite truncates the SINE more in the chimpanzee than the Xp/Yp telomere does in the human genome and, therefore, it is unlikely that a common ancestor contained an array of subterminal satellite at this chromosome end. No subterminal satellite sequences were identified in the gorilla sequences characterised in this report. However, subterminal satellite may be present in a more distal location because in situ hybridisation suggested that a block of subterminal satellite is present at the end of Xp/Yp in the gorilla (Di and Royle, unpublished observations). In the gorilla, the SINE was truncated still further by an array of telomere-like repeats, distal to which the gorilla sequence was homologous to sequences from the subterminal regions of human chromosomes 4p, 18p and 4q. The human 18p and 4q sequences contain an array of telomere-like repeats proximal to non-repetitive DNA, and the sequence is preserved in the gorilla in the same orientation and position relative to the flanking DNA (20 -22 ). A complex set of events must have occurred in the gorilla lineage to move subterminal sequences, and perhaps a distal array of subterminal satellite, from the end of an ancestral autosome to the end of Xp/Yp. In the orang-utans, two different structures, orL and orU, were identified at the Xp/Yp subterminal region. Immediately distal to the minisatellite sequence, orL contained telomere-like repeats that are probably at the start of the telomere. The SINE is absent from orL, whereas orU contained a SINE sequence, distal to which were some diverged telomere-like repeats, but it is not known whether they also represent the start of an Xp/Yp telomere. As discussed above, we cannot be certain that the orU structure has the same subspecies origin as the orL structure.

Table 2 . Comparison of the sequences at the positions that define the human Xp/Yp telomere-adjacent haplotypes with those found in chimpanzees, gorillas and orang-utans

Polymorphic positions identified in humans

Position from first telomere repeat in humans

-1888

-1018

-842

-652

-554

-544

-540

-427

-415

[Delta]373-363a

-338

-333

-298

-297

-176

-147

-146

-145

-73

-30

-13

Haplotypes

Orang-utan lower

C

C

C

G

*

*

*

G

C

*

*

*

*

*

*

*

*

*

*

*

*

Orang-utan upper

C

C

C

G

*

*

*

G

C

+

A

A

A

T

T

A

A

T

C

A

T

Gorilla

A

C

C

G

A

*

*

G

C

+

A

A

A

T

T

A

G

T

*

*

*

Chimpanzee

A

C

C

G

A

C

T

G

C

+

G

A

A

T

T

A

G

T

*

*

*

Ancestral haplotype

A/C

C

C

G

A

C

T

G

C

+

G/A

A

A

T

T

A

G/A

T

C

A

T

Caucasian haplotype A

G[kappa]

A

C

G

A

G

T

G

C

+

G

A

A

T

G

A

G

T

C

T

T

Caucasian haplotype B

A[kappa]

C

A

A

T

C

C

A

T

+

G

A

G

C

T

A

A

T

C

A

A

Caucasian haplotype C

A

C

A

A

A

G

T

G

T

+

G

A

G

C

T

A

G

T

C

A

A

West African haplotype A

nd

nd

C

G

A

C

C

G

C

-

A

C

A

T

G

G

G

C

G

T

nd

West African haplotype B

nd

nd

A

A

T

C

C

A

T

+

G

A

G

C

T

A

A

T

C

A

nd

West African haplotype C

nd

nd

A

A

A

G

T

G

T

+

G

A

G

C

T

A

G

T

C

A

nd

^aThe 10 bases between -363 and -373 are present (+) or absent (-) as indicated.nd = sequence not determined; *sequences not present in non-human primates [kappa] position not in complete linkage disequilibrium

Sequences equivalent to the human telomere-adjacent minisatellite were present in all the species analysed. It is monomorphic with four repeat units in humans and chimpanzees but just two repeats in both the orang-utan structures. However, in gorillas, this minisatellite has two alleles of three and four repeats. Minisatellites often exhibit length variation and they can be relatively transient over short periods of evolutionary time (30 ). Therefore, it is not possible to deduce the ancestral state of this minisatellite with any confidence. Curiously, a 45 bp duplication was identified in the chimpanzee and orang-utan orL but was absent in the human, gorilla and the orang-utan orU structures. The ancestral structure to these lineages could have contained this duplication, which has since been lost independently from three different lineages. Alternatively, the duplication may have occurred independently in the chimpanzee and orang-utan orL lineages.

These data suggest an ancestral structure for the Xp/Yp telomere junction region of the higher primates (Fig. 5 ). They also suggest that the terminal sequences of the great ape chromosomes are relatively transient, such that subterminal sequence organisation is unique to a lineage. This dynamism may reflect the ability of telomerase to heal broken chromosomes, resulting in the truncation of the chromosome and repositioning of the telomere, as seen for example in the human and possibly the orang-utan orL structure. However, the presence of subterminal satellite and structures other than a telomere in the chimpanzee and the gorilla indicates that the dynamics of subterminal sequences have also influenced the relative position of the Xp/Yp telomere.

Figure 5. The proposed ancestral state of the Xp/Yp telomere junction region of the Pongo/Gorilla/Pan/Homo lineage. The relevant structures are indicated above the line.

The orang-utan-specific minisatellite

A minisatellite composed of a 56 bp repeat was identified in both the orU and orL structures but it is present as only a monomer unit in humans, chimpanzees and gorillas. The transient nature of hypervariable minisatellites has already been described (30 ), so the appearance of a novel minisatellite only in orang-utans is in keeping with that observation. The minisatellite shows sequence variation between repeats, as well as repeat copy number variation which is probably amenable to analysis using minisatellite variant repeat mapping [MVR-PCR (31 ,32 )]. Although the full extent of the variability at this locus has not been determined, it may be useful for the analysis of orang-utan population structure in both wild and captive populations.

Sequence divergence

Unusually high levels of sequence divergence have been identified in the DNA orthologous to the human Xp/Yp telomere junction. In the human and probably the orang-utan genomes, the sequence is adjacent to a telomere. In contrast, the orthologous sequence is adjacent to a heterochromatic block of subterminal satellite in the chimpanzee genome and probably close to one in the gorilla genome. Little is known about the evolution of single copy sequences from heterochromatic regions, but it is possible that close proximity to heterochromatin or to a telomere has influenced the levels of inter-specific or inter-haplotypic sequence divergence (33 ).

Sequence ancestral to the human Xp/Yp telomere-adjacent haplotypes

Sequence variation was observed in both gorilla and orang-utan; none of the polymorphic sites detected in these species were the same as the polymorphic positions that define the human Xp/Yp haplotypes. The likely ancestral sequence for the human telomere-adjacent haplotypes has been determined by comparison of the Xp/Yp sequence data obtained from the chimpanzee, gorilla and orang-utan genomes (Table 2 ). It has not been possible to determine the ancestral state at three of the human polymorphic positions. Two of the sites (-338 and -146) are fixed for one or other of the polymorphic bases in the other three species. While it is tempting to speculate that these polymorphisms pre-date the separation of the human from the other lineages, the majority of the polymorphic positions are not shared between species and are therefore more recent. These data indicate that the highly diverged haplotypes in the DNA immediately adjacent to the human Xp/Yp telomere have evolved after the separation of the homo and pan lineages. The mechanisms underlying the generation and maintenance of such highly diverged haplotypes remain unresolved.

MATERIALS AND METHODS

Genomic DNAs

Human DNAs were lymphoblastoid DNAs from 80 unrelated individuals which constitute the parents of the CEPH families. Chimpanzee, gorilla and orang-utan genomic DNAs were extracted from blood and tissue samples obtained from captive bred animals.

PCR

PCRs were carried out using the buffer system described previously (32 ). Amplifications were carried out using a PTC-200 thermal cycler (MJ research) at 96°C for 20 s, 65°C for 30 s and 70°C for 1-4 min for 32 cycles; the annealing temperature was reduced to 55°C for weak or unsuccessful amplifications. DNA fragments from successful amplifications were resolved by agarose gel electrophoresis and purified from an agarose gel slice by centrifugation through glass wool.

Isolation of distal Xp/Yp sequences.

Isolation of distal Xp/Yp sequences from the gorilla genome was achieved by nested vectorette PCR (19 ) using the primer PrimB and the vectorette primer, followed by primer TSK8N with the vectorette primer. The vectorette was ligated to a Sau3AI site located 400 bp distal to the start of the interstitial block of telomere repeats identified in gorilla. The vectorette Vec1/MboI primer system has been described previously (34 ).

Isolation of the chimpanzee sequences distal to the point of divergence from the human sequence was achieved by PCR amplification using a 5' radioactively labelled primer PrimA [labelled in 10 µl reactions with 0.37 Mbq [[gamma]-³²P]ATP (Dupont NEN), 5 U of T4 polynucleotide kinase (GIBCO/BRL) and the manufacturers forward labelling buffer system] into the subterminal repeat array using primer Cht7B. The ladder of labelled fragments was resolved in denaturing polyacrylamide gel. 5' Radioactively labelled single-stranded DNA fragments were isolated from the polyacrylamide gel by removing the polyacrylamide containing the fragment from the backing paper. The polyacrylamide was soaked in 10 µl of water, and 1 µl was used to reamplify the fragment for further analysis.

PCR primer sequences

The primer sequences used were: TSK8M, 5'-ACCAGGTTTTCCAGTGTGTT-3'; TSK8N, 5'TCAGGAGTGAAGCTGCAGAC-3'; TSK8S, 5'-CACAAAGGACTCCCAGCCCT-3'; TS- K8R, 5'-CTTTCCCCAGCTATGGCTTC-3'; TSK8L, 5'-TCTTTTCATTGTKAGGTACTGATG-3'; PrimA, 5'-gcggtaCCCAAAGACAGAAGGCCCAG-3'; PrimB, 5'-gcggtaccGAACTGGG- TTATCGACCAGGT-3'; Cht7B, 5'-CCGCTATCTGTATAAACATGGAAA-3'; and 29c1B, 5'-TCTCTTTTTGGTCCGGTTCCCATC-3'. Lower case sequence represents 5' non- complementary tails containing restriction sites. For other primer sequences see (4 ).

The allele-specific primers used were: Gor4A, 5'-GTTACAGATGAGGAGCTCAC-3'; Gor4B, 5'-GTGAGCTCCTCATCTGTAAC-3'; OrangUp, 5'-GCATTCCTGGGAATTGCAGT-3'; and OrangLow, 5'-ACATTCCTGGGAATTGCGGA-3'.

DNA sequencing

Purified double-stranded DNA fragments (20-50 ng) were sequenced using Applied Biosystems DNA sequencing platforms and Applied Biosystems dye terminator sequencing chemistries. Contiguous sequences were assembled using the Applied Biosystems autoassembler programme (version 1.4) for Macintosh.

Southern analysis

Genomic DNA was digested to completion with restriction enzymes according to the manufacturer's recommendations (GIBCO/BRL). The digested DNAs were resolved by agarose gel electrophoresis and blotted onto Hybond-Nfp membrane (Amersham). Hybridisations were carried out using ³²P-labelled DNA probes (random hexaprime labelled) in the `blotto' hybridisation mix (35 ), at 65°C overnight. Unique sequence DNA probes were hybridised to genomic DNA Southern blots in 5× Denhardt's, 5× SSC and 1% SDS at 65°C overnight (35 ).

ACKNOWLEDGEMENTS

We thank A. J. Jeffreys, C. May, P. Bois and J. Buard for stimulating discussions and Y. Dubrova for help with statistics. N.J.R. is a UK-HGMP Senior Research Fellow. This work was funded by the Medical Research Council of Great Britain.

REFERENCES

1 Brown, W.R.A., Mackinnon, P.J., Villasante, A., Spurr, N., Buckle, V.J. and Dobson, M.J. (1990) Structure and polymorphism of human telomere-associated DNA. Cell, 63, 119-132.

2 Royle, N.J., Hill, M.C. and Jeffreys, A.J. (1992) Isolation of telomere junction fragments by anchored polymerase chain-reaction. Proc. R. Soc. Lond. B, 247, 57-61. MEDLINE Abstract

3 La Mantia, G., Pengue, G., Maglione, D., Pannuti, A., Pascucci, A. and Lania, L. (1989) Identification of new human repetitive sequences: characterization of the corresponding cDNAs and their expression in embryonal carcinoma-cells. Nucleic Acids Res., 17, 5913-5922. MEDLINE Abstract

4 Baird, D.M., Jeffreys, A.J. and Royle, N.J. (1995) Mechanisms underlying telomere repeat turnover, revealed by hypervariable variant repeat distribution patterns in the human Xp/Yp telomere. EMBO J., 14, 5433-5443. MEDLINE Abstract

5 Miyamoto, M.M., Koop, B.F., Slightom, J.L., Goodman, M. and Tennant, M.R. (1988) Molecular systematics of higher primates: genealogical relations and classification. Proc. Natl Acad. Sci. USA, 85, 7627-7631. MEDLINE Abstract

6 Cross, S., Lindsey, J., Fantes, J., Mckay, S., Mcgill, N. and Cooke, H. (1990) The structure of a subterminal repeated sequence present on many human chromosomes. Nucleic Acids Res., 18, 6649-6657. MEDLINE Abstract

7 de Lange, T., Shiue, L., Myers, R.M., Cox, D.R., Naylor, S.L., Killery, A.M. and Varmus, H.E. (1990) Structure and variability of human-chromosome ends. Mol. Cell. Biol., 10, 518-527. MEDLINE Abstract

8 Ijdo, J.W., Lindsay, E.A., Wells, R.A. and Baldini, A. (1992) Multiple variants in subtelomeric regions of normal karyotypes. Genomics, 14, 1019-1025. MEDLINE Abstract

9 Wilkie, A.O.M., Higgs, D.R., Rack, K.A., Buckle, V.J., Spurr, N.K., Fischelghodsian, N., Ceccherini, I., Brown, W.R.A. and Harris, P.C. (1991) Stable length polymorphism of up to 260 kb at the tip of the short arm of human chromosome-16. Cell, 64, 595-606.

10 Harris, P.C. and Thomas, S. (1992) Length polymorphism of the subtelomeric regions of both the short (p) and long arms (q) of chromosome16. Cytogenet. Cell Genet., 60, 171-172.

11 van Deutekom, J.C.T., Bakker, E., Lemmers, R.J.L.F., Vanderwielen, M.J.R., Bik, E., Hofker, M.H., Padberg, G.W. and Frants, R.R. (1996) Evidence for subtelomeric exchange of 3.3 kb tandemly repeated units between chromosomes 4q35 and 10q26: implications for genetic counseling and etiology of FSHD1. Hum. Mol. Genet., 5, 1997-2003.

12 Louis, E.J. and Haber, J.E. (1992) The structure and evolution of subtelomeric-Y repeats in Saccharomyces cerevisiae. Genetics, 131, 559-574. MEDLINE Abstract

13 Louis, E.J., Naumova, E.S., Lee, A., Naumov, G. and Haber, J.E. (1994) The Chromosome end in yeast: its mosaic nature and influence on recombinational dynamics. Genetics, 136, 789-802. MEDLINE Abstract

14 Royle, N.J., Baird, D.M. and Jeffreys, A.J. (1994) A subterminal satellite located adjacent to telomeres in chimpanzees is absent from the human genome. Nature Genet., 6, 52-56. MEDLINE Abstract

15 Cooke, H.J., Brown, W.R.A. and Rappold, G.A. (1985) Hypervariable telomeric sequences from the human sex-chromosomes are pseudoautosomal. Nature, 317, 687-692. MEDLINE Abstract

16 Inglehearn, C.F. and Cooke, H.J. (1990) A VNTR immediately adjacent to the human pseudoautosomal telomere. Nucleic Acids Res., 18, 471-476. MEDLINE Abstract

17 Weber, B., Weissenbach, J. and Schempp, W. (1987) Conservation of human-derived pseudoautosomal sequences on the sex-chromosomes of the great apes. Cytogenet. Cell Genet., 45, 26-29. MEDLINE Abstract

18 Weber, B., Weissenbach, J. and Schempp, W. (1988) X-Y crossing over in the chimpanzee. Hum. Genet., 80, 301-303. MEDLINE Abstract

19 Arnold, C. and Hodgson, I.J. (1991) Vectorette PCR: a novel approach to genome walking. PCR Methods Applications, 1, 39-42.

20 Flint, J. (New EMBL Z95704).

21 Morii, K., Macina, R., Negorev, D., Hu, X.L., Ruthig, L., Spais, C. and Riethman, H. (GenBank U32384).

22 Dickson, M.C., Heather, L.J., Lyle, R., van Deutekom, J.C.T., Clark, L.N., van Geel, M., Wright, T.J., Frants, R.R. and Hewitt, J.E. (GenBank U74496).

23 Jones, M.L. (1969) In Hofer, H. O. (ed.), Recent Advances in Primatology. Karger, Basel, pp. 217-223.

24 Seuanez, H.N., Evans, H.J., Martin, D.E. and Fletcher, J. (1979) An inversion of chromosome 2 that destinguishes between Bornean and Sumatran orangutans. Cytogenet. Cell Genet., 23, 137-140. MEDLINE Abstract

25 Zhi, L., Karesh, W.B., Janczewski, D.N., Fraziertaylor, H., Sajuthi, D., Gombek, F., Andau, M., Martenson, J.S. and Obrien, S.J. (1996) Genomic differentiation among natural-populations of orangutan (Pongo pygmaeus). Curr. Biol., 6, 1326-1336. MEDLINE Abstract

26 Markham, R.J. (1985) Captive orang-utans: present status and future prospects. Bull. Zool. Manag., 23, 31-36.

27 Perrin-Pecontal, P., Gouy, M., Nigon, V.M. and Trabuchet, G. (1992) Evolution of the primate beta-globin gene region: nucleotide sequence of the delta-beta-globin intergenic region of gorilla and phylogenetic-relationships between african apes and man. J. Mol. Evol., 34, 17-30. MEDLINE Abstract

28 Mohammad-Ali, K., Eladari, M.E. and Galibert, F. (1995) Gorilla and orangutan c-myc nucleotide sequences: inference on hominoid phylogeny. J. Mol. Evol., 41, 262-276. MEDLINE Abstract

29 Alvarez, V., Coto, E., Setien, F., Gonzalezroces, S. and Lopezlarrea, C. (1996) Molecular evolution of the N-formyl peptide and C5a receptors in nonhuman-primates. Immunogenetics, 44, 446-452. MEDLINE Abstract

30 Gray, I.C. and Jeffreys, A.J. (1991) Evolutionary transience of hypervariable minisatellites in man and the primates. Proc. R. Soc. Lond. B, 243, 241-253. MEDLINE Abstract

31 Jeffreys, A.J., Neumann, R. and Wilson, V. (1990) Repeat unit sequence variation in minisatellites: a novel source of DNA polymorphism for studying variation and mutation by single molecule analysis. Cell, 60, 473-485. MEDLINE Abstract

32 Jeffreys, A.J., MacLeod, A., Tamaki, K., Neil, D.L. and Monckton, D.G. (1991) Minisatellite repeat coding as a digital approach to DNA typing. Nature, 354, 204-209. MEDLINE Abstract

33 Luke, S. and Verma, R.S. (1995) Human (Homo sapiens) and chimpanzee (Pan troglodytes) share similar ancestral centromeric alpha satellite DNA sequences but other fractions of heterochromatin differ considerably. Am. J. Phys. Anthropol., 96, 63-71. MEDLINE Abstract

34 Allen, M.J., Collick, A. and Jeffreys, A.J. (1994) Use of vectorette and subvectorette PCR to isolate transgene flanking DNA. PCR Methods Appl., 4, 71-75. MEDLINE Abstract

35 Sambrook, J., Fritsch, E.F. and Maniatis, T. (1989) Molecular Cloning: A Laboratory Manual. 2nd edn. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY.

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*To whom correspondence should be addressed. Tel: +44 116 2522270; Fax: +44 116 2523378; Email: njr@leicester.ac.uk

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