Genetics of Gracilaria sp. (Rhodophyceae, Gigartinales). IV. Mitotic recombination and its relationship to mixed phases in the life history

Abstract

The long-standing problem of mixed phases in life histories of red algae was investigated by genetic techniques. Diploid tetrasporophytes of Gracilaria sp. growing in culture produced functional male and female gametangia in addition to tetraspores. Sporelings resulting from fertilizations involving these gametangia were polyploid, their chromosome numbers indicating that gametes from the tetrasporophyte were diploid. The tetrasporophytes themselves were heterozygous for two genes affecting plant colour. These markers were observed to become homozygous in twin spots of recombinant tissue at the same time that gametangia were formed. All the observations are consistent with the interpretation that both gametangia and recombinant twin spots arise as a consequence of mitotic recombination. The broader implications of these observations for the Rhodophyceae are discussed.