This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Sexual reproduction usually reshuffles genetic information, creating offspring that differ from their parents. But one small plant takes an unexpected route.
In a new study published in Nature, an international team led by André Marques at the Max Planck Institute for Plant Breeding Research in Cologne has shown that the Brazilian beak-sedge Rhynchospora tenuis reproduces sexually—producing pollen, fertilizing its egg cells and setting seeds—but has completely lost the reshuffling of DNA between chromosomes from each parent. The offspring retained the same genetic makeup as their mothers, effectively mimicking clonal reproduction. Most sexually reproducing organisms rely on meiosis, a specialized form of cell division that produces reproductive cells, during which homologous chromosomes inherited from each parent exchange DNA segments.
These crossovers generate genetic diversity and ensure accurate chromosome segregation; without them, fertility can be compromised. Earlier cytological studies suggested that male meiosis in R. tenuis proceeds without crossovers. However, it remained unclear whether genetic recombination—normally generating new combinations of parental genes in offspring—is absent in both sexes and, if so, how the plant still ensures proper chromosome segregation and maintains fertility.
Rhynchospora tenuis appears to have overcome this problem. Among flowering plants, R. tenuis has the lowest known chromosome number. Its chromosomes also have an unusual organization—the centromere activity spreads across the chromosome's entire length, known as holocentric chromosomes.
In addition, the plant performs meiosis in a reversed order, an alternative cell-division pathway, separating duplicated chromosome copies before separating their matching partners. Together, these features of unusual genome architecture may allow reproduction to continue even without crossovers. The researchers combined detailed genome assemblies from nine plants collected in Brazil with chromosome imaging, sequencing of individual pollen nuclei and controlled crossing experiments.
Across more than 10,000 pollen nuclei, the team detected no crossovers and also obtained no evidence of chromosome exchanges through the female reproductive pathway. Using independent approaches of cytological, genomic, single-cell and developmental analysis, the findings provide evidence for a complete absence of crossovers in both male and female meiosis, a combination documented for the first time in an otherwise sexually reproducing species. Strikingly, the team discovered that inheritance is strongly biased.
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