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      Cytogenetic characterisation and chromosomal mapping of microsatellite and telomeric repeats in two gecko species (Reptilia, Gekkonidae) from Thailand

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          Studies of chromosomes of Cyrtodactylus jarujini Ulber, 1993 and C. doisuthep Kunya et al., 2014 to compare microsatellite and TTAGGG sequences by classical and molecular techniques were conducted in Thailand. Karyological typing from a conventional staining technique of C. jarujini and C. doisuthep showed diploid chromosome numbers of 40 and 34 while the Fundamental Numbers (NF) were 56 in both species. In addition, we created the chromosome formula of the chromosomes of C. jarujini showing that 2n (40) = L sm 1 + L sm 2 + L t 3 + M m 1 + M t 4 + S m 2 + S a 2 + S t 5 while that of C. doisuthep was 2n (34) = L sm 3 + L m 2 + L t 3 + M m 1 + M t 2 + S m 4 + S a 1 + S t 1. Ag-NOR staining revealed NOR-bearing chromosomes in chromosome pairs 13 and 14 in C. jarujini , and in chromosome pairs 9 and 13 in C. doisuthep . This molecular study used the FISH technique, as well as microsatellite probes including (A) 20, (TA) 15, (CGG) 10, (CGG) 10, (GAA) 10, (TA) 15 and TTAGGG repeats. The signals showed that the different patterns in each chromosome of the Gekkonids depended on probe types. TTAGGG repeats showed high distribution on centromere and telomere regions, while (A) 20, (TA) 15, (CGG) 10, (CGG) 10, (GAA) 10 and (TA) 15 bearing dispersed over the whole genomes including chromosomes and some had strong signals on only a pair of homologous chromosomes. These results suggest that the genetic linkages have been highly differentiated between the two species.

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          Microsatellite accumulation on the Y chromosome in Silene latifolia.

          The dioecious plant Silene latifolia possesses evolutionarily young sex chromosomes, and so serves as a model system to study the early stages of sex chromosome evolution. Sex chromosomes often differ distinctly from autosomes in both their structure and their patterns of evolution. The S. latifolia Y chromosome is particularly unique owing to its large size, which contrasts with the size of smaller, degenerate mammalian Y chromosomes. It is thought that the suppression of recombination on the S. latifolia Y chromosome could have resulted in the accumulation of repetitive sequences that account for its large size. Here we used fluorescence in situ hybridization (FISH) to study the chromosomal distribution of various microsatellites in S. latifolia including all possible mono-, di-, and tri-nucleotides. Our results demonstrate that a majority of microsatellites are accumulated on the q arm of the Y chromosome, which stopped recombining relatively recently and has had less time to accumulate repetitive DNA sequences compared with the p arm. Based on these results we can speculate that microsatellites have accumulated in regions that predate the genome expansion, supporting the view that the accumulation of repetitive DNA sequences occurred prior to, not because of, the degeneration of genes.
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            Microsatellites: simple sequences with complex evolution.

             Hans Ellegren (2004)
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              Microsatellite distribution on sex chromosomes at different stages of heteromorphism and heterochromatinization in two lizard species (Squamata: Eublepharidae: Coleonyx elegans and Lacertidae: Eremias velox)

              Background The accumulation of repetitive sequences such as microsatellites during the differentiation of sex chromosomes has not been studied in most squamate reptiles (lizards, amphisbaenians and snakes), a group which has a large diversity of sex determining systems. It is known that the Bkm repeats containing tandem arrays of GATA tetranucleotides are highly accumulated on the degenerated W chromosomes in advanced snakes. Similar, potentially homologous, repetitive sequences were found on sex chromosomes in other vertebrates. Using FISH with probes containing all possible mono-, di-, and tri-nucleotide sequences and GATA, we studied the genome distribution of microsatellite repeats on sex chromosomes in two lizard species (the gecko Coleonyx elegans and the lacertid Eremias velox) with independently evolved sex chromosomes. The gecko possesses heteromorphic euchromatic sex chromosomes, while sex chromosomes in the lacertid are homomorphic and the W chromosome is highly heterochromatic. Our aim was to test whether microsatellite distribution on sex chromosomes corresponds to the stage of their heteromorphism or heterochromatinization. Moreover, because the lizards lie phylogenetically between snakes and other vertebrates with the Bkm-related repeats on sex chromosomes, the knowledge of their repetitive sequence is informative for the determination of conserved versus convergently evolved repetitive sequences across vertebrate lineages. Results Heteromorphic sex chromosomes of C. elegans do not show any sign of microsatellite accumulation. On the other hand, in E. velox, certain microsatellite sequences are extensively accumulated over the whole length or parts of the W chromosome, while others, including GATA, are absent on this heterochromatinized sex chromosome. Conclusion The accumulation of microsatellite repeats corresponds to the stage of heterochromatinization of sex chromosomes rather than to their heteromorphism. The lack of GATA repeats on the sex chromosomes of both lizards suggests that the Bkm-related repeats on sex chromosomes in snakes and other vertebrates evolved convergently. The comparison of microsatellite sequences accumulated on sex chromosomes in E. velox and in other eukaryotic organisms suggests that historical contingency, not characteristics of particular sequences, plays a major role in the determination of which microsatellite sequence is accumulated on the sex chromosomes in a particular lineage.

                Author and article information

                Comp Cytogenet
                Comp Cytogenet
                Comparative Cytogenetics
                Pensoft Publishers
                02 February 2021
                : 15
                : 1
                : 41-52
                [1 ] Walai Rukhavej Botanical Research institute, Mahasarakham University, Kantharawichai, Maha Sarakham, Thailand Mahasarakham University Maha Sarakham Thailand
                [2 ] Biology program, Faculty of Science and Technology, Phetchabun Rajabhat University, Phetchabun, 67000, Thailand Phetchabun Rajabhat University Phetchabun Thailand
                [3 ] Program of Biology, Faculty of Science, Khon Kaen University, Muang, Khon Kaen, 40002, Thailand Khon Kaen University Khon Kaen Thailand
                [4 ] Department of Fishery, School of Agriculture and Natural Resources, University of Phayao, Muang, Phayao, 56000, Thailand University of Phayao Phayao Thailand
                Author notes
                Corresponding author: Sumalee Phimphan ( joodoof@ 123456gmail.com )

                Academic editor: N. Golub

                Weera Thongnetr, Surachest Aiumsumang, Rodjarin Kongkaew, Alonglod Tanomtong, Chatmongkon Suwannapoom, Sumalee Phimphan

                This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

                Research Article
                Molecular Biology


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