Marsupial Cytogenetics

1989 ◽  
Vol 37 (3) ◽  
pp. 331 ◽  
Author(s):  
DL Hayman
Keyword(s):  
X Chromosome ◽  
Dna Sequences ◽  
Chromosome Numbers ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Repeated Dna ◽  
Chromosome X ◽  
X Chromosomes ◽  
Repeated Dna Sequences ◽  
Chromosome Mosaicism

This review includes a list of the chromosome numbers of marsupials and a summary of the main features of chromosome evolution in this group of mammals. Special topics discussed include sex chromosome mosaicism, the size of the marsupial X chromosome, X chromosomes and nucleolar organisers, complex sex chromosome systems, repeated DNA sequences and aspects of meiosis.

Repeated DNA sequences in the distal long arm of the human X chromosome

1986 ◽  
Vol 74 (1) ◽  
Author(s):  
U. M�ller ◽  
U. Tantravahi ◽  
A. Monaco ◽  
Helene Stroh ◽  
L.M. Kunkel ◽  
...  
Keyword(s):  
X Chromosome ◽  
Dna Sequences ◽  
Repeated Dna ◽  
Repeated Dna Sequences

scholarly journals Sequence Differentiation Associated With an Inversion on the Neo-X Chromosome of Drosophila americana

Genetics ◽  
2003 ◽  
Vol 165 (3) ◽  
pp. 1317-1328 ◽  
Author(s):  
Bryant F McAllister
Keyword(s):  
X Chromosome ◽  
Sex Chromosomes ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Geographic Region ◽  
Sex Chromosome Evolution ◽  
Sequence Analyses ◽  
X Chromosomes ◽  
Y Chromosomes ◽  
Chromosomal Pair

Abstract Sex chromosomes originate from pairs of autosomes that acquire controlling genes in the sex-determining cascade. Universal mechanisms apparently influence the evolution of sex chromosomes, because this chromosomal pair is characteristically heteromorphic in a broad range of organisms. To examine the pattern of initial differentiation between sex chromosomes, sequence analyses were performed on a pair of newly formed sex chromosomes in Drosophila americana. This species has neo-sex chromosomes as a result of a centromeric fusion between the X chromosome and an autosome. Sequences were analyzed from the Alcohol dehydrogenase (Adh), big brain (bib), and timeless (tim) gene regions, which represent separate positions along this pair of neo-sex chromosomes. In the northwestern range of the species, the bib and Adh regions exhibit significant sequence differentiation for neo-X chromosomes relative to neo-Y chromosomes from the same geographic region and other chromosomal populations of D. americana. Furthermore, a nucleotide site defining a common haplotype in bib is shown to be associated with a paracentric inversion [In(4)ab] on the neo-X chromosome, and this inversion suppresses recombination between neo-X and neo-Y chromosomes. These observations are consistent with the inversion acting as a recombination modifier that suppresses exchange between these neo-sex chromosomes, as predicted by models of sex chromosome evolution.

scholarly journals The X chromosome of the German cockroach, Blattella germanica, is homologous to a fly X chromosome despite 400 million years divergence

BMC Biology ◽  
2019 ◽  
Vol 17 (1) ◽  
Author(s):  
Richard P. Meisel ◽  
Pablo J. Delclos ◽  
Judith R. Wexler
Keyword(s):  
Sex Determination ◽  
X Chromosome ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Blattella Germanica ◽  
German Cockroach ◽  
Whole Genome Sequence ◽  
Sex Chromosome Evolution ◽  
X Chromosomes

Abstract Background Sex chromosome evolution is a dynamic process that can proceed at varying rates across lineages. For example, different chromosomes can be sex-linked between closely related species, whereas other sex chromosomes have been conserved for > 100 million years. Cases of long-term sex chromosome conservation could be informative of factors that constrain sex chromosome evolution. Cytological similarities between the X chromosomes of the German cockroach (Blattella germanica) and most flies suggest that they may be homologous—possibly representing an extreme case of long-term conservation. Results To test the hypothesis that the cockroach and fly X chromosomes are homologous, we analyzed whole-genome sequence data from cockroaches. We found evidence in both sequencing coverage and heterozygosity that a significant excess of the same genes are on both the cockroach and fly X chromosomes. We also present evidence that the candidate X-linked cockroach genes may be dosage compensated in hemizygous males. Consistent with this hypothesis, three regulators of transcription and chromatin on the fly X chromosome are conserved in the cockroach genome. Conclusions Our results support our hypothesis that the German cockroach shares the same X chromosome as most flies. This may represent the convergent evolution of the X chromosome in the lineages leading to cockroaches and flies. Alternatively, the common ancestor of most insects may have had an X chromosome that resembled the extant cockroach and fly X. Cockroaches and flies diverged ∼ 400 million years ago, which would be the longest documented conservation of a sex chromosome. Cockroaches and flies have different mechanisms of sex determination, raising the possibility that the X chromosome was conserved despite the evolution of the sex determination pathway.

scholarly journals The X chromosome of the German cockroach, Blattella germanica, is homologous to a fly X chromosome despite 400 million years divergence

2018 ◽  
Author(s):  
Richard P Meisel ◽  
Pablo J Delclos ◽  
Judith R Wexler
Keyword(s):  
Sex Determination ◽  
X Chromosome ◽  
Chromosome Evolution ◽  
Sex Chromosome ◽  
Blattella Germanica ◽  
German Cockroach ◽  
Whole Genome Sequence ◽  
Sex Chromosome Evolution ◽  
X Chromosomes

AbstractBackgroundSex chromosome evolution is a dynamic process that can proceed at varying rates across lineages. For example, different chromosomes can be sex-linked between closely related species, whereas other sex chromosomes have been conserved for >100 million years. Cases of long-term sex chromosome conservation could be informative of factors that constrain sex chromosome evolution. Cytological similarities between the X chromosomes of the German cockroach (Blattella germanica) and most flies suggest that they may be homologous—possibly representing an extreme case of long-term conservation.ResultsTo test the hypothesis that the cockroach and fly X chromosomes are homologous, we analyzed whole genome sequence data from cockroach. We found evidence in both sequencing coverage and heterozygosity that a significant excess of the same genes are on both the cockroach and fly X chromosomes. We also present evidence that the candidate X-linked cockroach genes may be dosage compensated in hemizygous males. Consistent with this hypothesis, three regulators of transcription and chromatin on the fly X chromosome are conserved in the cockroach genome.ConclusionsOur results support our hypothesis that the German cockroach shares the same X chromosome as most flies. This may represent convergent evolution of the X chromosome in the lineages leading to cockroaches and flies. Alternatively, the common ancestor of most insects may have had an X chromosome that resembled the extant cockroach and fly X. Cockroaches and flies diverged ∼400 million years ago, which would be the longest documented conservation of a sex chromosome. Cockroaches and flies have different mechanisms of sex determination, raising the possibility that the X chromosome was conserved despite evolution of the sex determination pathway.

scholarly journals Bisection of the X chromosome disrupts the initiation of chromosome silencing during meiosis in Caenorhabditis elegans

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Yisrael Rappaport ◽  
Hanna Achache ◽  
Roni Falk ◽  
Omer Murik ◽  
Oren Ram ◽  
...  
Keyword(s):  
Caenorhabditis Elegans ◽  
Rna Polymerase Ii ◽  
X Chromosome ◽  
Sex Chromosomes ◽  
Sex Chromosome ◽  
Transcription Analysis ◽  
X Chromosomes ◽  
Unique Character ◽  
Active Transcription ◽  
Heterogametic Sex

AbstractDuring meiosis, gene expression is silenced in aberrantly unsynapsed chromatin and in heterogametic sex chromosomes. Initiation of sex chromosome silencing is disrupted in meiocytes with sex chromosome-autosome translocations. To determine whether this is due to aberrant synapsis or loss of continuity of sex chromosomes, we engineered Caenorhabditis elegans nematodes with non-translocated, bisected X chromosomes. In early meiocytes of mutant males and hermaphrodites, X segments are enriched with euchromatin assembly markers and active RNA polymerase II staining, indicating active transcription. Analysis of RNA-seq data showed that genes from the X chromosome are upregulated in gonads of mutant worms. Contrary to previous models, which predicted that any unsynapsed chromatin is silenced during meiosis, our data indicate that unsynapsed X segments are transcribed. Therefore, our results suggest that sex chromosome chromatin has a unique character that facilitates its meiotic expression when its continuity is lost, regardless of whether or not it is synapsed.

Highly repeated DNA sequences in birds: The structure and evolution of an abundant, tandemly repeated 190-bp DNA fragment in parrots

Genomics ◽  
1992 ◽  
Vol 14 (2) ◽  
pp. 462-469 ◽  
Author(s):  
Cort S. Madsen ◽  
Dineke H. de Kloet ◽  
Jean E. Brooks ◽  
Siwo R. de Kloet
Keyword(s):  
Dna Sequences ◽  
Repeated Dna ◽  
Repeated Dna Sequences ◽  
Highly Repeated Dna ◽  
Dna Fragment
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