Codominant inheritance of polymorphic color variants of Gracilaria domingensis (Gracilariales, Rhodophyta)

Agar is the most valuable phycocoloid in the world market. Currently, about half of its production is obtained from the red alga Gracilaria (Gracilari ales, Rhodophyta). Consequently, this genus has been the subject of many st udies worldwide. A common green color variant of G. domingensis (Kutzing) S onder ex Dickie was found in a natural population on the northeastern coast of Brazil. Crosses were performed to determine the mode of color inheritan ce. The results can be interpreted as the expression of a pair of codominan t alleles, where the green and red phenotypes are homozygous, and the heter ozygotes present a brownish color. Heterozygous tetrasporophytes, at least until they are 4-5 cm long, exhibit a parental influence on the female game tophyte, since the reddish-brown or greenish-brown color is dependent on th e female parent color (red or green). Mixed reproductive phases, as well as specimens with patches of different colors bearing spermatangia or cystoca rps, were observed in laboratory cultures. Gametophytes that resulted from in situ germination of meiospores were also observed, and could be easily d etected when red or green gametophytes were grown on brown tetrasporophytes .