Frans Alfons Janssens (Sint-Niklaas 23 July 1865 - Wichelen, 8 October 1924). Ordained as a priest in 1886. He obtained a PhD in Natural Science with the highest honors and a scholarchip to attend the most prestigious foreign laboratories. He worked with Professor Kjeldahl at the Hansen Institute Carlsberg Brewery in Copenhagen. He was also a teacher at the St. Lawrence Brewery School in Ghent. In 1896, he became a professor at the Faculty of Sciences for the Katholieke Universiteit Leuven, as a chair in microscopy and later in cytology, succeeding Jean-Baptiste Carnoy in the chair. He is the discoverer of the crossing-over of genes during meiosis, which he called 'chiasmatypie'. His work was continued by the Nobel Prize winner Thomas Hunt Morgan to develop the theory of genetic linkage.
He was also the president of the Societé Belge de Biologie and a Canon (priest) at the Sint-Baafskathedraal in Ghent.
In 1953, the Katholieke Universiteit Leuven founded the 'F.A.Janssens Genetics Laboratory', in recognition for the scientific merits of Frans Alfons Janssens. The laboratory is currently known as the 'Center for Microbial and Plant Genetics'.
Janssens was the son of politician Theodoor Janssens.