Mendelian nightmares: The germline-restricted chromosome of songbirds

Pavel Borodin, Augustin Chen, Wolfgang Forstmeier, Simone Fouché, Lyubov Malinovskaya, Yifan Pei, Radka Reifová, Francisco J. Ruiz-Ruano, Stephen A. Schlebusch, Manuelita Sotelo-Muñoz, Anna Torgasheva, Niki Vontzou, Alexander Suh

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Germline-restricted chromosomes (GRCs) are accessory chromosomes that occur only in germ cells. They are eliminated from somatic cells through programmed DNA elimination during embryo development. GRCs have been observed in several unrelated animal taxa and show peculiar modes of non-Mendelian inheritance and within-individual elimination. Recent cytogenetic and phylogenomic evidence suggests that a GRC is present across the species-rich songbirds, but absent in non-passerine birds, implying that over half of all 10,500 bird species have extensive germline/soma genome differences. Here, we review recent insights gained from genomic, transcriptomic, and cytogenetic approaches with regard to the genetic content, phylogenetic distribution, and inheritance of the songbird GRC. While many questions remain unsolved in terms of GRC inheritance, elimination, and function, we discuss plausible scenarios and future directions for understanding this widespread form of programmed DNA elimination.
Original languageEnglish
Pages (from-to)255–272
Number of pages18
JournalChromosome Research
Issue number2-3
Early online date13 Apr 2022
Publication statusPublished - Sep 2022


  • B chromosome
  • Chromosome elimination
  • Germline-restricted chromosome
  • Germline/soma genome difference
  • Non-Mendelian inheritance

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