HOMOEOLOGOUS CHROMOSOME PAIRING AND RESTRICTED SEGREGATION IN THE FERN CERATOPTERIS

The segregation of a marker characterized by pale green gametophytes was monitored within an inbreeding study of the polyploid fern Ceratopteris. Although all of the sporophytes showing segregation were derived from the self-fertilization of haploid gametophytes, a low overall frequency of 2.5% pale gametophytes was observed in the F₃–F₅ generations. A model based upon a duplicated locus and homoeologous chromosome pairing can explain the segregational behavior within the study. The overall level of homoeologous pairing was determined to be 10%. Occasionally, green gametophytes that were presumably heterozygous for the marker contained pale sectors. This behavior may involve mitotic crossing-over between homoeologous chromosomes.