The Almost Final Answer on What Determines Sex

Here is an article regarding the postulated ways in which it is thought that C. sativa (includding spp. indica and ruderalis) sex is predetermined (or not) by various factors including genetics and environmental factors. I am reposting this for those who are versed in science; be warned - if you don't have a strong background in biology, much of this may not make sense.
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Summary by -D9-
It seems that indeed sex is to an extent *pre-determined* when the seed is formed, before it even germinates due to male genetic markers reported fairly recently while trying to determine the factors influencing the sex of Cannabis. However, as plants are tricky when it comes to sex, many do in fact change sex during their lifespan, either partly or completely. This, however, is probably due to factors that fall back on genetics in C. sativa (spp.). As many know, chemical treatments with hormones such as gibberellin will induce male phenotypic traits to emerge (notably flowers), at least locally on a plant. This is most likely due to the activation of male genetic markers already present in the plant due to the hormonal treatment, thus the chemical treatment is actually activating either part(s) of, or complete, gene(s) responsible for male sex phenotypes in C. sativa, regardless of genotype. A comparrison might be made to sexual reassignment in humans: When a female human wishes to become male (or as much so as possible), large ammounts of testosterone are provided to the patient, along with treatments that supress very strongly almost all female differentiating hormones. This leads to more masculine traits to become dominant, such as a deepened pitch in the voice, facial hair, and other associated traits found in male humans, while also reducing the feminine traits such as breast size, reorganization of the storage of addipose tissue, and other factors. Obviously, in humans this also requires surgical intervention to be as complete as possible, but due to the flexibility of plants and their complex genetic structure (many plants are much more genetically complex than humans), this can be circumvented when dealing with C. sativa (spp.). Thus, chemical treatment, along with environmental factors can indeed impact sex in plants, and in many cases can define the sex of a plant.

Conclusions resulting from examining the sexual distinction characteristics inherent in Drosophila (spp.) (the fly) and destinctions between monoecious and dioecious varieties further aid in our understanding of what makes a plant male or female. As I have previously postulated, the sexual manifestation in C. sativa is much more complex than a simple XY system as is found in humans; however, it now appears to be yet even more complicated than I had thought. In dioecious types, a heteromorphic sexual type has been identified, which would indicate that in some instances (strains), a plant may indeed be extremely dependent on environmental factors with regard to sex. This is very speculative however, and most of this evidence has not been directly related to C. sativa (spp.) sativa / indica, which are much more valued by horticulturists interested in the floral phenotypes (sex). Furthermore, this work was not exhaustive, and much is still unknown regarding the specific methodology used during these studies.

Most recently, several geneticists have identified male related gene markers now thought to be part of an at present unknown chromosomal sex differentiation system present in C. sativa (spp.). These types of markers are frequently found when attenpting to karyotype an organism (determine complete and accurate chromosomal structure and purpose), and may lead to the future discovery of the complete sex differentiation modality in the species. At the present time, with male markers identified, and the report of possible heteromorphic sex destinction in some plants, it is plausible to assume that if a female flower can be forced to form male flowering parts through hormone induction, it is not out of the question to conceive the idea of reversing this process by using typically female hormones in a phenotypically male plant in an attempt to produce a female flower. If some male plants are not specifically genetically selected to be male by an absolute chromosomal distinction as is the case with the XY system, then it would be (in theory) possible to take an undifferentiated plant exhibiting male phenotypic traits and induce a female phenotypic response following the addition of feminizing hormones. Once the sex differentiation process is better understood in the species, it may be possible to hormonally alter male plants to exhibit female traits in the spp. of interest. If this is the case, a process may be developed to selectively mask all male traits of a plant, forcing it to become phenotypically female. This would be an extremely important discovery in the genetic engineering of C. sativa spp., and could ultimately lead to some of the most potent and true breeding strains ever produced. It would also allow for an estimated 78% increase in total yield per harvest overall, due to the fact that many initially male plants may be forced to flower as females, and be harvested as such rather than being discarded as waste.

Until the exact mechanism by which sex determination is elucidated however, it is important to entertain the notion that environmental factors can, but not always, have an extreme impact on the sex distinction of a plant.

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The Article

Mechanisms of sex determination:
Cannabis has been described as having one of the most complicated mechanisms of sex determination among the dioecious plants.[17] Many models have been proposed to explain sex determination in Cannabis.

Based on studies of sex reversal in hemp, it was first reported by K. Hirata in 1924 that an XY sex-determination system is present.[14] At the time, the XY system was the only known system of sex determination. The X:A system was first described in Drosophila spp in 1925.[18] Soon thereafter, Schaffner disputed Hirata's interpretation,[19] and published results from his own studies of sex reversal in hemp, concluding that an X:A system was in use and that furthermore sex was strongly influenced by environmental conditions.[15]

Since then, many different types of sex determination systems have been discovered, particularly in plants.[10] Dioecy is relatively uncommon in the plant kingdom, and a very low percentage of dioecious plant species have been determined to use the XY system. In most cases where the XY system is found it is believed to have evolved recently and independently.[20]

Since the 1920s, a number of sex determination models have been proposed for Cannabis. Ainsworth[10] describes sex determination in the genus as using "an X/autosome dosage-type."

The question of whether heteromorphic sex chromosomes are indeed present is most conveniently answered if such chromosomes were clearly visible in a karyotype. Cannabis was one of the first plant species to be karyotyped, however, this was in a period when karyotype preparation was primitive by modern standards (see History of Cytogenetics). Heteromorphic sex chromosomes were reported to occur in staminate individuals of dioecious 'Kentucky' hemp, but were not found in pistillate individuals of the same variety. Dioecious 'Kentucky' hemp was assumed to use an XY mechanism. Heterosomes were not observed in analyzed individuals of monoecious 'Kentucky' hemp, nor in an unidentified German cultivar. These varieties were assumed to have sex chromosome composition XX.[21] According to other researchers, no modern karyotype of Cannabis had been published as of 1996.[22] Proponents of the XY system state that Y chromosome is slightly larger than the X, but difficult to differentiate cytologically.[23]

More recently, Sakamoto and various co-authors[24][25] have used RAPD to isolate several genetic marker sequences that they name Male-Associated DNA in Cannabis (MADC), and which they interpret as indirect evidence of a male chromosome. Several other research groups have reported identification of male-associated markers using RAPD and AFLP.[26][16][27] Ainsworth commented on these findings, stating that "It is not surprising that male-associated markers are relatively abundant. In dioecious plants where sex chromosomes have not been identified, markers for maleness indicate either the presence of sex chromosomes which have not been distinguished by cytological methods or that the marker is tightly linked to a gene involved in sex determination."[10]

Environmental sex determination is known to occur in a variety of species.[28] Many researchers have suggested that sex in Cannabis is determined or strongly influenced by environmental factors.[15] Ainsworth reviews that treatment with auxin and ethylene have feminizing effects, and that treatment with cytokinins and gibberellins have masculinizing effects.[10] It has been reported that sex can be reversed in Cannabis using chemical treatment.[29] A PCR-based method for the detection of female-associated DNA polymorphisms by genotyping has been developed.[30]

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