Cannabis is a genus of flowering plants that includes three putative species, Cannabis sativa L., Cannabis indica Lam., and Cannabis ruderalis Janisch. These three taxa are indigenous to central Asia and surrounding regions.
Industrial hemp products are made from Cannabis plants selected to produce an abundance of fiber and minimal levels of THC (Ä9- tetrahydrocannabinol), the psychoactive molecule that produces the "high" associated with marijuana. The drug consists of dried flowers and leaves of plants selected to produce high levels of THC. Various extracts including hashish and hash oil are also produced. The cultivation and possession of Cannabis for recreational use is outlawed in most countries.
Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions. At the top of a flowering plant, this number again diminishes to a single leaflet per leaf. The lower leaf pairs usually occur in an opposite leaf arrangement and the upper leaf pairs in an alternate arrangement on the main stem of a mature plant.
Cannabis usually has imperfect flowers with staminate "male" and pistillate "female" flowers occurring on separate plants, although hermaphroditic flowers sometimes occur. Male flowers are borne on loose panicles, and female flowers are borne on racemes. It is not unusual for individual plants to bear both male and female flowers in some strains, a condition called monoecy. On monoecious plants, flowers of both sexes may occur on separate inflorescences, or on the same inflorescence.
Cannabinoids, terpenoids, and other volatile compounds are secreted by glandular trichomes that occur most abundantly on the floral calyxes and bracts of female plants.
All known strains of Cannabis are wind-pollinated and produce "seeds" that are technically called achenes. Most strains of Cannabis are short day plants, with the possible exception of C. sativa subsp. sativa var. spontanea (= C. ruderalis), which is commonly described as "auto-flowering" and may be day-neutral.
Cannabis is naturally diploid, having a chromosome complement of 2n=20, although polyploid individuals have been artificially produced. Cannabis is a genus of flowering plant which includes one or more species. The plant is believed to have originated in the mountainous regions just north west of the Himalayas. It is also known as hemp, although this term usually refers to varieties of Cannabis cultivated for non-drug use. Cannabis plants produce a group of chemicals called cannabinoids which produce mental and physical effects when consumed. As a drug it usually comes in the form of dried buds or flowers(marijuana), resin (hashish), or various extracts collectively known as hashish oil. In the early 20th century, it became illegal in most of the world to cultivate or possess Cannabis for drug purposes.
Cannabis is predominantly dioecious, although many monoecious varieties have been described. Subdioecy (the occurrence of monoecious individuals and dioecious individuals within the same population) is widespread. Many populations have been described as sexually labile.
As a result of intensive selection in cultivation, Cannabis exhibits many sexual phenotypes that can be described in terms of the ratio of female to male flowers occurring in the individual, or typical in the cultivar. Dioecious varieties are preferred for drug production, where the female plants are preferred. Dioecious varieties are also preferred for textile fiber production, whereas monoecious varieties are preferred for pulp and paper production. It has been suggested that the presence of monoecy can be used to differentiate between licit crops of monoecious hemp and illicit dioecious drug crops.
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. At the time, the XY system was the only known system of sex determination. The was first described in Drosophila spp in 1925. Soon thereafter, Schaffner disputed Hirata's interpretation, 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.
Since then, many different types of sex determination systems have been discovered, particularly in plants. 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.
Since the 1920s, a number of sex determination models have been proposed for Cannabis. Ainsworth 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. According to other researchers, no modern karyotype of Cannabis had been published as of 1996. Proponents of the XY system state that Y chromosome is slightly larger than the X, but difficult to differentiate cytologically.
More recently, Sakamoto and various co-authors 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. 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."
Environmental sex determination is known to occur in a variety of species. Many researchers have suggested that sex in Cannabis is determined or strongly influenced by environmental factors. Ainsworth reviews that treatment with auxin and ethylene have feminizing effects, and that treatment with cytokinins and gibberellins have masculinizing effects. It has been reported that sex can be reversed in Cannabis using chemical treatment. A PCR-based method for the detection of female-associated DNA polymorphisms by genotyping has been developed.
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