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Cytoplasmic male sterility
Many species of plants with bisexual flowers and occasionally monoecious there are few individuals with sterile male generative organs. These facts were known to Darwin. He regarded them as a kind of tendency to move from monoecious to dioecious, which in evolutionary thought better. Thus, the formation of individuals with male sterility, is a natural phenomenon of evolution. Male sterility was first discovered by K.Correns in 1904 at the garden plants summer savory. In 1921, B.Batson found it in linen, in 1924 a geneticist D. Jones - for onions, in 1929 A.I.Kuptsov - in sunflower. Later it was found that male sterility is widely spread among flowering plants. The mutations that cause male sterility are described now in most crop plants.
Male sterility is the absence of pollen or her incapable of. Genetic male sterility genes could be due to the sterility of the nucleus and the interaction of genes and nuclear plazmogenes. According to the two types of male sterility: the nuclear, or gene, and cytoplasmic. Nuclear sterility is caused by mutations of chromosomal genes ms. Due to the fact that the genes of sterility are recessive and fertility genes are dominant, and the type of inheritance of sterility from crossing sterile plants with fertile F1 all plants are fertile (msms x MsMs Msms), and F2 is split on the fertile and sterile forms against 3:1 in the next generation, the number of sterile plants from such crosses decreases continuously. It was being developed methods using genetic techniques to produce sterile hybrids of cotton, sunflower and other crops.
To explain the causes of cytoplasmic sterility were put forward three hypotheses. One of them, known as viral, links the emergence of male sterility with a viral infection that can be transmitted through sexual reproduction through the cytoplasm of the egg. The second hypothesis considers the emergence of CMS as a result of non-compliance of the cytoplasm and nuclei of different species in the distant hybridization. Indeed, in some cases, such as when crossing wheat Triticum aestivum with Tr Aestivum, there are forms to CMS. However, many cultures found CMS is not related to a distant hybridization. Therefore, the greatest recognition, is now has a hypothesis that considers the emergence of CMS as a result of specific mutations plazmogenes.
As a result of learning and generalization of experimental data on the inheritance of male sterility rise to the notion that this property is due to the interaction of the cytoplasm of chromosomes and genes, collectively known as the genetic system. Cytoplasm, which determines pollen sterility, called Cyts (sterile cytoplasm), and the cytoplasm, giving plants with fertile pollen-Cytn (normal cytoplasm). There are localized in the chromosomes of a dominant gene RF (from the initial letters of restoring fertility-restoring fertility), which, without changing the structure and specificity of sterile cytoplasm, at the same time prevent its manifestation. Sterile cytoplasm exerts its effect only in combination with recessive alleys of this gene. Therefore, only the combination of Cyts rfrf may make development of sterile pollen. Fertile pollen is formed on the basis of normal cytoplasm combinations Cytn RfRf, Cytn Rfrf and Cytn rfrf and on the basis of sterile cytoplasm in combination Cyts RfRf and Cyts Rfrf. Thus inheritance CMS maternal possible only in crossing plants Cyts rfrf x Cytn rfrf Cyts rfrf (sterility is fixed).Crossbreeding Cyts rfrf x Cytn (s) RfRf all plants will fertile, a complete restoration of fertility.
The immediate cause of the forms with a CMS, some scientists considered a violation of protein synthesis as a result of mutations in the nucleus, leading to incorrect microsporogenesis other degeneration of pollen grains attributed to disruption in supply of sterile anthers of plants.
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