Synaptonemal complex and crossing-over: structural support or interference?

Positive cross-over interference is attributed to the prevention of crossing-over by the growing synaptonemal complex. This conjecture is based on a report in the literature that the selection of prospective cross-over sites may actually precede a proper synapsis of homologous chromosomes during meiotic prophase. A genetic test of this notion is suggested using a properly marked trisomic configuration, applicable to a variety of organisms.