Biologists at UC Davis have discovered a remarkable genetic mechanism in walnut trees that enables them to switch between male and female flowers each season, a trait that has persisted for approximately 40 million years. Their findings, published in Science, reveal that walnut trees consistently exhibit two flowering patterns, either starting the season with male (“male-first”) or female (“female-first”) flowers. This dynamic approach helps avoid self-pollination and was first noted by Charles Darwin in 1877. Jeff Groh and Professor Graham Coop conducted genomic sequencing on walnut species and identified two variants of a gene responsible for these flowering types, which have remained stable over millennia. Interestingly, the mechanism mirrors animal sex determination systems, such as X and Y chromosomes in humans, maintaining a balance of genetic variation. In addition, the researchers explored a similar phenomenon in pecan trees, suggesting that both walnuts and pecans evolved comparable flowering mechanisms through different genetic paths. This research not only enhances our understanding of plant reproduction but also offers insights into broader evolutionary processes. Overall, this work highlights the intricate relationship between genetics and flowering patterns and their implications for understanding sex determination across species.
