Origin of Amniote Sex Chromosomes: An Ancestral Super-Sex Chromosome, or Common Requirements?
The diversity of sex chromosomes among amniotes is the product of independent evolution of different systems in different lineages, defined by novel sex-determining genes. Convergent evolution is very common, suggesting that some genes are particularly adept at taking on a sex-determining role. Comparative gene mapping, and more recently whole genome sequencing, have now turned up other surprising relationships; different regions of the amniote genome that have become sex determining in some taxa seem to share synteny, or share sequence, in others. Is this, after all, evidence that these regions were once linked in a super...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Ezaz, T., Srikulnath, K., Graves, J. A. M. Tags: Symposium article Source Type: research
Sex Determination, Sex Chromosomes, and Karyotype Evolution in Insects
Insects harbor a tremendous diversity of sex determining mechanisms both within and between groups. For example, in some orders such as Hymenoptera, all members are haplodiploid, whereas Diptera contain species with homomorphic as well as male and female heterogametic sex chromosome systems or paternal genome elimination. We have established a large database on karyotypes and sex chromosomes in insects, containing information on over 13000 species covering 29 orders of insects. This database constitutes a unique starting point to report phylogenetic patterns on the distribution of sex determination mechanisms, sex chromoso...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Blackmon, H., Ross, L., Bachtrog, D. Tags: Symposium article Source Type: research
A Century of Sex Determination in Flowering Plants
Plants have evolved a diverse array of strategies for sexual reproduction, particularly through the modification of male and female organs at distinct points in development. The immense variation in sexual systems across the land plants provides a unique opportunity to study the genetic, epigenetic, phylogenetic, and ecological underpinnings of sex determination. Here, we reflect on more than a century of research into flowering plant sex determination, placing a particular focus on the foundational genetic and cytogenetic observations, experiments, and hypotheses. Building on the seminal work on the genetics of plant sex,...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Harkess, A., Leebens-Mack, J. Tags: Symposium article Source Type: research
Accumulation of Deleterious Mutations on the Neo-Y Chromosome of Japan Sea Stickleback (Gasterosteus nipponicus)
Degeneration of Y chromosomes is a common evolutionary path of XY sex chromosome systems. Recent genomic studies in flies and plants have revealed that even young neo-sex chromosomes with the age of a few million years show signs of Y degeneration, such as the accumulation of nonsense and frameshift mutations. However, it remains unclear whether neo-Y chromosomes also show rapid degeneration in fishes, which often have homomorphic sex chromosomes. Here, we investigated whether a neo-Y chromosome of Japan Sea stickleback (Gasterosteus nipponicus), which was formed by a Y-autosome fusion within the last 2 million years, accu...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Yoshida, K., Makino, T., Kitano, J. Tags: Symposium article Source Type: research
Dynamic Sequence Evolution of a Sex-Associated B Chromosome in Lake Malawi Cichlid Fish
B chromosomes are extra chromosomes found in many species of plants, animals, and fungi. B chromosomes often manipulate common cellular processes to increase their frequency, sometimes to the detriment of organismal fitness. Here, we characterize B chromosomes in several species of Lake Malawi cichlid fish. Whole genome sequencing of Metriaclima zebra "Boadzulu" individuals revealed blocks of sequence with unusually high sequence coverage, indicative of increased copy number of those sequences. These regions of high sequence coverage were found only in females. SNPs unique to the high copy number sequences permitted the de...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Clark, F. E., Conte, M. A., Ferreira-Bravo, I. A., Poletto, A. B., Martins, C., Kocher, T. D. Tags: Symposium article Source Type: research
Chromosome-Specific Centromere Sequences Provide an Estimate of the Ancestral Chromosome 2 Fusion Event in Hominin Genomes
Human chromosome 2 is a product of a telomere fusion of two ancestral chromosomes and loss/degeneration of one of the two original centromeres. Genomic signatures of this event are limited to inverted telomeric repeats at the precise site of chromosomal fusion and to the small amount of relic centromeric sequences that remain on 2q21.2. Unlike the site of fusion, which is enriched for sequences that are shared elsewhere in the human genome, the region of the nonfunctioning and degenerate ancestral centromere appears to share limited similarity with other sites in the human genome, thereby providing an opportunity to study ...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Miga, K. H. Tags: Symposium article Source Type: research
Horizontal Transfer Can Drive a Greater Transposable Element Load in Large Populations
Genomes are comprised of contrasting domains of euchromatin and heterochromatin, and transposable elements (TEs) play an important role in defining these genomic regions. Therefore, understanding the forces that control TE abundance can help us understand the chromatin landscape of the genome. What determines the burden of TEs in populations? Some have proposed that drift plays a determining role. In small populations, mildly deleterious TE insertion alleles are allowed to fix, leading to increased copy number. However, it is not clear how the rate of exposure to new TE families, via horizontal transfer (HT), can contribut...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Groth, S. B., Blumenstiel, J. P. Tags: Symposium article Source Type: research
A Half-Century of Studies on a Chromosomal Hybrid Zone of the House Mouse
The first natural chromosomal variation in the house mouse was described nearly 50 years ago in Val Poschiavo on the Swiss side of the Swiss–Italian border in the Central Eastern Alps. Studies have extended into neighboring Valtellina, and the house mice of the Poschiavo-Valtellina area have been subject to detailed analysis, reviewed here. The maximum extent of this area is 70 km, yet it has 4 metacentric races and the standard 40-chromosome telocentric race distributed in a patchwork fashion. The metacentric races are characterized by highly reduced diploid numbers (2n = 22–26) resulting from Robertsonian fus...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Gimenez, M. D., Förster, D. W., Jones, E. P., Johannesdottir, F., Gabriel, S. I., Panithanarak, T., Scascitelli, M., Merico, V., Garagna, S., Searle, J. B., Hauffe, H. C. Tags: Symposium article Source Type: research
Estimating Diversity of Black Flies in the Simulium ignescens and Simulium tunja Complexes in Colombia: Chromosomal Rearrangements as the Core of Integrative Taxonomy
Black flies (Diptera: Simuliidae) are distributed throughout the world, with more than 2200 formally described species. The family is renowned for its high frequency of cryptic species, offering an opportunity for integrative taxonomy, based on morphological, chromosomal, and molecular approaches. The biodiversity within Simulium (Psilopelmia) ignescens and S. (Psilopelmia) tunja in Colombia was estimated from the larval stage; 10 morphoforms were recognized based on 7 structural characters. This remarkable morphological variation was evaluated through 23 markers on the polytene chromosomes. We established 1 new cytoform i...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Colorado-Garzon, F. A., Adler, P. H., Garcia, L. F., Munoz de Hoyos, P., Bueno, M. L., Matta, N. E. Tags: Symposium article Source Type: research
The Evolution of Genome Structure by Natural and Sexual Selection
This article reviews progress in understanding how chromosome inversions and sex chromosomes evolve, and how their evolution affects species’ ecology. Analyses of clines in inversion frequencies in flies and mosquitoes imply strong local adaptation, and roles for both over- and under dominant selection. Those results are consistent with the hypothesis that inversions become established when they capture locally adapted alleles. Inversions can carry alleles that are beneficial to closely related species, causing them to introgress following hybridization. Models show that this "adaptive cassette" scenario can trigger ...
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Kirkpatrick, M. Tags: Symposium article Source Type: research
Chromosome Evolution: Molecular Mechanisms and Evolutionary Consequences
(Source: Journal of Heredity)
Source: Journal of Heredity - December 13, 2016 Category: Research Authors: Peichel, C. L. Tags: Guest Editorial Source Type: research
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(Source: Journal of Heredity)
Source: Journal of Heredity - December 13, 2016 Category: Research Tags: Cover / Standing Material Source Type: research
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(Source: Journal of Heredity)
Source: Journal of Heredity - December 13, 2016 Category: Research Tags: Cover / Standing Material Source Type: research
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(Source: Journal of Heredity)
Source: Journal of Heredity - December 13, 2016 Category: Research Tags: Cover / Standing Material Source Type: research
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(Source: Journal of Heredity)
Source: Journal of Heredity - December 13, 2016 Category: Research Tags: Cover / Standing Material Source Type: research
