Can you never remember all seven of Snow White’s dwarfs? Then try the seven traits studied in peas by Mendel. Smooth or wrinkled seeds, yellow or green seeds, white or purple flowers… I used to stop there until I read about the latest study in Nature. Joining forces, the John Innes Centre in Norwich, UK, and the Institute of Agricultural Genomics in Shenzhen, China, have identified Mendel’s remaining genes—solving a conundrum in the history of science and laying the groundwork for a leap forward in the genetic improvement of a food crop that is nutritious but too often overlooked by geneticists.

Of course, in the 19th century, Gregor Mendel didn’t know about DNA and wasn’t talking about genes, but about “factors.” In the age of modern genetics—and now genomics—it was inconceivable to continue ignoring which genes those traits corresponded to.

The first Mendel gene to be identified, back in 1990, was the one controlling seed shape. In some varieties, seeds shrivel when dried and taste sweet when eaten fresh. The key gene codes for an enzyme that converts sugars into starch. The dominant variant fills seeds with starch and keeps them smooth, while the recessive variant leaves more sugar.

Subsequently, genes for three more Mendelian traits were discovered: plant height, flower color, and seed color. But three remained elusive: pod color, pod shape, and flower arrangement.

It took six years of work to uncover them, using a collection of 700 varieties with 155 million polymorphisms (SNPs) compared to the reference sequence. Noel Ellis, Noam Chayut, Shifeng Cheng, and colleagues discovered that the yellow (rather than green) color of pods is due to a deletion in a gene involved in chlorophyll synthesis. This mechanism is different from that of seed color, which depends on a gene responsible for degrading the pigment.

Pod shape, on the other hand, depends on two mutations that affect cell wall thickening. Depending on the allelic variant, the pod may or may not be edible. Finally, a deletion in another gene causes changes in flower arrangement on the plant.

The Sino-British tour de force also enabled the study of many other traits, beyond the original seven that founded Mendelian genetics. Notably, this was accomplished without relying on gene editing, which has yet to be adapted to Pisum sativum. For more details, see the news reports in Science and Nature.