The Sexual Cycle and Intercrossing in the Genus <i>Astrephomene</i>*

Abstract

SYNOPSIS. The structure and certain aspects of the physiology of the sexual cycle, including mating and zygote germination, were studied in strains of the colonial green flagellate Astrephomene gubernaculifera . Mating type inheritance was analyzed in 4 crosses among strains with 7 chromosomes and 1 cross between strains with 4 chromosomes. Results in all cases indicated that mating type was under the control of a single pair of alleles. Twenty‐six morphologically identical clones from separate geographic areas were studied with regard to sexual compatibility. On the basis of intercrossing, 6 sexually isolated groups were recognized. Complete gene flow (genetic compatibility) was found among the strains comprising intercrossing Group I.