Old but not (so) degenerated--slow evolution of largely homomorphic sex chromosomes in ratites.Recombination arrest is a necessary step for the evolution of distinct sex chromosomes. Structural changes, such as inversions, may represent the mechanistic basis for recombination suppression and comparisons of the structural organization of chromosomes as given by chromosome-level assemblies offer the possibility to infer inversions across species at some detail. In birds, deduction of the process of sex chromosome evolution has been hampered by the lack of a validated chromosome-level assembly from a representative of one of the two basal clades of modern birds, Paleognathae. We therefore developed a high-density genetic linkage map of the ostrich Z chromosome and used this to correct an existing assembly, including correction of a large chimeric superscaffold and the order and orientation of other superscaffolds. By comparing the order and location of genes on the ostrich Z chromosome with that of six bird species from the other major clade of birds Neognathae , and of reptilian outgroup species, 25 Z-linked inversions were inferred in the avian lineages. We defined Z chromosome organization in an early avian ancestor and identified inversions spanning the candidate sex-determining DMRT1 gene in this ancestor, which could potentially have triggered the onset of avian sex chromosome evolution. This study illustrates the need for validated chromosome-level assemblies for inference of genome evolution.
Author information: DNA-based sex tests now exist for many avian species. However, none of these tests are widely applicable to ratites. We present DNA sequence data for a locus that is W chromosome-linked in the kiwi, ostrich, cassowary, rhea, and emu. At the amino acid level, this sequence has significant homology to X-linked genes in platyfish and Caenorhabditis elegans. Polymerase chain reaction PCR primers designed to this locus allow the assignment of sex in all species of living ratites.
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Author information: Ellegren ebc. Degeneration of the nonrecombining chromosome is a common feature of sex chromosome evolution, readily evident by the presence of a pair of largely heteromorphic chromosomes, like in eutherian mammals and birds. However, in ratites order Palaeognathae, including, e. To better understand what may limit sex chromosome evolution, we performed ostrich transcriptome sequencing and studied genes from the nonrecombining region of the W chromosome. Fourteen gametologous gene pairs present on the W chromosome and Z chromosome were identified, with synonymous sequence divergence of 0. The location of these genes on the Z chromosome was consistent with a sequential increase in divergence, starting and ending Ma. On the basis of the occurrence of Z-linked genes hemizygous in females, we estimate that about one-third of the Z chromosome does not recombine with the W chromosome in female meiosis.
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Ratite Sex Chromosomes
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Keywords: kW1 sequenceNeognathous birdsPaleognathous birds Ratite Repetitive sequenceReptilesSex chromosome differentiation. Cytogenet Genome Res ; Morphological differentiation of sex chromosomes in three species of ratite birds. H.A.. Ansari. N. Our results suggest that the evolution of sex chromosomes has occurred .. One is that the sex chromosomes of ratites and non-ratite birds originate from.
Sex determination in the representatives of the superorder Ratite birds - test of blood The sex in birds is determined by sex chromosomes Z and W. The female. Chromosomes were studied in female specimens of the ostrich, Struthio camelus L., analysis with regard to the differentiation of the sex-chromosomes. Abstract. Recombination arrest is a necessary step for the evolution of distinct sex chromosomes. Structural changes, such as inversions, may.