1. Sustained heterozygosity across a self-incompatibility locus in an inbred ascidian.
- Author
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Satou Y, Hirayama K, Mita K, Fujie M, Chiba S, Yoshida R, Endo T, Sasakura Y, Inaba K, and Satoh N
- Subjects
- Animals, Animals, Inbred Strains physiology, Chromosomes, Ciona intestinalis physiology, Genetic Loci, Genetic Variation, Self-Fertilization, Sequence Analysis, DNA, Animals, Inbred Strains genetics, Ciona intestinalis genetics, Heterozygote
- Abstract
Because self-incompatibility loci are maintained heterozygous and recombination within self-incompatibility loci would be disadvantageous, self-incompatibility loci are thought to contribute to structural and functional differentiation of chromosomes. Although the hermaphrodite chordate, Ciona intestinalis, has two self-incompatibility genes, this incompatibility system is incomplete and self-fertilization occurs under laboratory conditions. Here, we established an inbred strain of C. intestinalis by repeated self-fertilization. Decoding genome sequences of sibling animals of this strain identified a 2.4-Mbheterozygous region on chromosome 7. A self-incompatibility gene, Themis-B, was encoded within this region. This observation implied that this self-incompatibility locus and the linkage disequilibrium of its flanking region contribute to the formation of the 2.4-Mb heterozygous region, probably through recombination suppression. We showed that different individuals in natural populations had different numbers and different combinations of Themis-B variants, and that the rate of self-fertilization varied among these animals. Our result explains why self-fertilization occurs under laboratory conditions. It also supports the concept that the Themis-B locus is preferentially retained heterozygous in the inbred line and contributes to the formation of the 2.4-Mb heterozygous region. High structural variations might suppress recombination, and this long heterozygous region might represent a preliminary stage of structural differentiation of chromosomes., (© The Author 2014. Published by Oxford University Press on behalf of the Society for Molecular Biology and Evolution. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)
- Published
- 2015
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