Frans Alfons Janssens (Sint-Niklaas 23 July 1865 - Wichelen, 8 October 1924) was Catholic priest and the discoverer of 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.
Frans Janssens was the son of Theodoor Janssens, a politician.
He was ordained as a priest in 1886 and obtained a PhD in Natural Science with the highest honors and a scholarship to attend many prestigious foreign laboratories.
Janssens then worked with Professor Kjeldahl at the Hansen Institute Carlsberg Brewery in Copenhagen and was a teacher at the St.
Lawrence Brewery School in Ghent.
In 1896, he became a professor at the Faculty of Sciences for the Catholic University of Leuven, as a chair in microscopy and later in cytology, succeeding Jean-Baptiste Carnoy in the chair.