Abstract
The random amplified polymorphic DNA (RAPD) technique was employed in the haplo‐diploid dioecious species Gracilaria gracilis to identify sex‐linked PCR markers. Sixty‐nine decamer oligonucleotide primers were tested on two bulks of DNA, one from five haploid males and the other from five haploid females. One of these primers (OPD13) generated a 430‐bp fragment specific to males and a 620‐bp fragment specific to females. The diploid individuals (tetrasporophytes) showed the co‐occurrence of these two fragments. In order to verify the linkage between the sexual phenotypes and these markers, a progeny array of 59 haploid individuals (male and female) born on a diploid individual was analysed, in all of which the two markers produced by the OPD13 primer segregated perfectly with sex.