currently the only feasible means for production of haploids in cotton is via semigamy. Haploids produced by semigamy can be used to facilitate selection Semigamy is a type of facultative apomixis in which incotton(GossypiumbarbadenseL.)breedingandgenemapping.The the male sperm nucleus does not fuse with the egg objectivesofthepresentstudyweretodetailthegeneticmechanismof nucleus after penetrating the egg in the embryo sac. Subsemigamy and its relationship with reduction in chlorophyll content. Pima 57-4, a semigametic line isolated as a doubled haploid (DH) sequent development can give rise to an embryo confrom Pima S-1, produced 46 to 50% haploid progeny when selfed. taining haploid chimeral tissues of paternal and materComparedwithitsnaturalisogeniclineS-1,57-4hadlowerleafchloro- nal origins. In cotton, the semigametic phenomena was phyll content, photosynthetic rate (Pn), and boll weight, and had first reported by Turcotte and Feaster (1963), who dehigher lint percentage, seed index, and shorter and coarser fiber. veloped the Pima line 57-4 that produced haploid seeds Three segregating populations (F2 and two BC1F1) from a cross of at a high frequency. The semigametic line was a DH 57-4 S-1 were progeny tested to investigate the genetic basis of from a natural haploid mutant found in a field of Pima semigamy. Haploid production in F1 ,F 2, and backcrosses were also S-1. In two presentations, Turcotte and Feaster (1974, recorded. The results verified that semigamy in cotton is controlled 1975) indicated that semigamy in Pima appeared to be by one gene, previously designated Se. The gene functions sporophytcontrolled by one dominant gene (Se). Despite wide ically and gametophytically, resulting in incomplete dominance nature. A generation-mean analysis for the cross of 57-4 S-1 identified acceptance by the cotton research community (Kohel one gene responsible for the parental differences in chlorophyll con- and Lewis, 1984; Smith and Cothren, 1999), no compretent. Consistent with the difference between the two parental isogenic hensive genetic data have been published. Semigametic lines, semigameticF2.3 lineshad significantlylower chlorophyllcontent lines can produce 30 to 60% haploids when self pollithan nonsemigametic F2.3 lines, an observation that was confirmed by nated, and about 0.7 to 1.0% androgenic haploids when a significant association between haploid production and chlorophyll used as female parents in crosses with normal nonsemicontent. The Se gene and the gene for reduced chlorophyll content gametic cottons (Chaudhari, 1978, 1979; Turcotte and could be either the same or closely linked. The elucidation of the Feaster, 1967). A unique feature of semigamy is that relationship between semigamy and fiber development will help charthe inheritance of the gene is conveyed by both male acterize the molecular function of the semigametic gene. and female gametes, but expression of the trait in terms of haploid production occurs only in the female parent. As a consequence, for example, in reciprocal crosses