In 1909, cytologist Frans Janssens described microscopic chromosomal structures that were viewed during prophase I of ; he called these structures

meiosis; chiasmata

Explanation:

The linkage between two non-sister chromatids of homologous chromosomes can be seen in the diplotene stage of prophase I of meiosis which is called chiasmata.

This phenomenon is discovered in 1909 by a  Frans Janssens who called the structure chaismata. Chaismata allows the exchange of genes between two homologous chromosomes which came from two parents.

In the pachytene stage crossing over between non-sister chromatids takes place. This crossing over helps in increasing the genetic variability in the gametes and offspring.  

a chain link fence because there so tiny even my albino donkey can't get out