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The social gene 鄭先祐 (Ayo) 國立台南大學 環境生態研究所 The social gene 12.1 Introduction 12.2 Genes as strategists (基因作為策略者) 12.3 Variant genes 12.4 The reach of the strategic gene (策略性基因) 12.5 The prokaryotic firm: managing a cytoplasmic commons (原核公司:經營一個細胞質公共財) 12.6 Dangerous liaisons (聯繫) 12.7 Plasmid protection rackets 12.8 Team substitutions Social gene 2 12.9 Multicellular corporations 12.10 A chimeric menagerie (供展覽用的野生動物) 12.11 The nuclear citadel (要塞) 12.12 The sexual revolution 12.13 The open society and its enemies 12.14 The eukaryotic alliance 12.15 Sex chromosomes 12.16 Genomic imprinting and the altercation of generations 12.17 Reprise (再出現) Social gene 3 12.1 Introduction 於天擇下演化的複雜行為和構造,可視為 對適應的基因的選擇,而不是對個體 (vehicles) 的選擇。 個體只是基因遺傳個工具。 對這樣的說法之批評:個體才是一個生命 體,其體內的某個基因,倘若沒有其他許 多基因的協助,往往無法遺傳下去。 然而,個別基因可視為整體基因(個體和群 體)social groups的成员。 Social gene 4 This chapter emphasizes the current state of genetical systems, and ask why conserved feature of organisms are evolutionarily stable relative to conceivable(可理解的) alternatives. Gene-centred theories are often reviled(謾罵) because of their perceived implications for human societies. Social gene 5 12.2 Genes as strategists Gene are catalysis. 基因所獲取的利益是在個體上,個體的 reproductive success,以及這個個體的大部份 基因的遺傳。 倘若再加上個體與其親緣關係的個體,整體 的某個基因的inclusive fitness,這時個體的利 益和基因的利益就不一定一致。 這時基因可以扮演 strategists,而不是個體。 Social gene 6 12.3 Variant genes 個體的基因,如同一本書的文字。 這本書有多少字? Material genes 使用多少字彙? Informational genes 於 informational genes 中,有部份是strategic gene(策略性基因),可於 evolutionary game中, 扮演 strategist (策略者)。 A strategic gene corresponds to a set of material genes and can be considered the unit of adaptive innovation. Social gene 7 12.4 The reach of the strategic gene Dawkins (1976) a thought-experiment Considered the possibility of a gene that caused its possessors to develop a green beard and to be nice to other green-bearded individuals. 綠鬍子效應(green-beard effect),策略性基因 因為選擇性的差異,而形成 linkage disequilibrium (Box 12.1) Species boundaries are a major cause of Linkage disequilibrium. Social gene 8 Linkage disequilibrium 1. A new mutation 2. Epistatic selection generates linkage disequilibrium because it causes a gene to leave more descendants when it is present in some combinations than in others. 3. Sampling effects can cause linkage disequilibrium in small populations. Social gene 9 12.5 The prokaryotic firm: managing a cytoplasmic commons 原核公司:經營細胞質公共財 Genetic replication makes use of energy and substrates that are supplied by the metabolic economy in much greater quantities than be possible without a genetic division of labour. These materials are common goods (公共財), available to every gene in the cytoplasm. Thus, genetic communities are potentially vulnerable to free-riders, genes that take more than they contribute. Social gene 10 DNA-based replicators are believed to have evolved from RNA-based replicators, possibly because DNA is copied with greater fidelity (忠 誠) than RNA (Lazcano, et al., 1988). The change also had implications for cellular security. DNA運用m-RNA,且需要隨時清除m-RNA, 如此可以避免有 RNA-based parasite. Social gene 11 12.6 Dangerous liaisons (聯繫) Cosmides and Tooby (1981) called a set of genes that replicated together, and whose fitness was maximized in the same way, a coreplicon.(核心組) 倘若一個個體內有兩個以上的 coreplicon,這 將會有利益的衝突。 細菌有多個circular genomes One is the bacterial chromosome The extra circles are called plasmids. Social gene 12 細菌的plasmid 通常是一些特別的 metabolic skills. 譬如:antibiotic resistance 於細菌交接的過程,通常只有plasmid傳送。 Such a plasmid may be essential in the presence of antibiotics but a burden in their absence. 這是有風險的交接 (譬如有病毒) 細菌的plasmid的遺傳,可以有vertical and horizontal兩種。 Social gene 13 12.7 Plasmid protection rackets Plasmid once acquired, are difficult to discard. Many plasmids encode a persistent “poison” and its short-lived “antidote”. Thus, if a cell segregates without the plasmid, it is cut off from its supply of antidote and succumbs to the poison. The gene for the poison can be said to recognize the presence or absence of the gene for the antidote. Social gene 14 Mitochondria Mitochondria contain a large DNA maxi-circle and many small mini-circles. The maxicircle encodes essential genes in garbled form (斷章不全的形式), whereas the minicircles encode guide RNAs. Could RNA enditing have evolved as a minicircle maintenance system? If so, one would predict that minicircles can also edit DNS and encrypt maxicircle genes in ways that only they can decipher (解讀). Social gene 15 12.8 Team substitutions (換組员) A non-recombining bacterial chromosome is a team that does not change its members (except by mutation). Its social contract is ‘all for one, and one for all’, not ‘every gene for itself’. 細菌的chromosomal recombination 只有在結合 (conjugation)或是病毒感染(transduction)時,才 有可能生。 但有些細菌演化出可以從環境取用DNA取代 其內的某段相同的部份。(這有recombination) Social gene 16 Uptake of DNA is induced under conditions of nutritional stress and may have evolved primarily as a means of gaining nutrients. Why should a team replace one of its members? The repair hypothesis views transformation as a means of replacing injured team members (damaged DNA). 但是這個假說難成立,因為uptake of DNA is not induced by damage to the chromosome. The recombinant-progeny hypothesis views transformation as a means of trying out new players. (於惡劣的環境,更換不同的組员) Social gene 17 12.9 Multicellular corporations The development of resistant spores by Bacillus subtilis illustrates the differentiation of soma and germ line in simple form. 某個細菌進行unequal cell division 產生a mother cell (soma) and a prespore (germ line). The mother cell engulfs the prespore, assists in formation of the spore coat and is then discarded. 當環境營養缺乏時,細菌會犧牲mother cell (soma),而投入 spore (germ line). Social gene 18 多細胞公司 生物發展somas to gain the benefits of a cellular division of labour (分工). 但是soma 是擁有資源者,可能被其他germ lines 剝削資源。 因此soma 必要對其產出的germ lines有「信心」 (基因必要是相同) 當soma 愈來愈大愈複雜,soma 和 germ lines 的關係愈來愈不直接,這讓parasites 有機可 趁。因此免疫機制 (immune surveillance) 必 要產生。 Social gene 19 於vertebrate immune system 發展出 T-cell receptors, major histocompatibility complex (MHC) antigens and immunoglobulins 補充資料 (生物學 免疫系統) Social gene 20 Specific responses Two kinds of lymphocytes play a critical role in the specific responses. These are the B-cells and the T-cells. B-cells are specialized to do two things plasma cells make antibodies to combat the invader. (humoral immunity) memory B-cells 記憶過去曾經產生過的抗體 資料。 Social gene 21 cellular immunity T-cells are involved in cellular immunity. There are three basic kinds of T-cells. Helper T-cells (幫助者), interact with other cells to enhance the immune response. cytotoxic T-cells (殺手), identify infected cells and rupture their membranes suppressor T-cells (壓抑), help call off the body's defenses. Social gene 22 抗原-抗體反應 Antigens are foreign molecules that elicit an immune response in the host organism. Antibodies are proteins produced by the host plasma cells that identify and help destroy antigens, including the cells that bear antigens. Social gene 23 Fig. 20.4 巨喫細胞 Fig. 20.5 When a specific antigen is encountered, the recognition regions of the antibody molecules attach to specific binding sites on the antigen that can be engulfed by a macrophage. Social gene 24 Fig. 20.6 In the ongoing combat against invaders. 巨喫細胞吞食抗原, 再將抗原送至膜外。 Helper T-cell 受到激發, 分泌interleukin。 Interleukin刺激 cytotoxic T-cells和 memory cells的 production. Social gene 25 Fig. 20.7 B-cells begin their own arousal by capturing antigen and preparing a recognition site that will match that of a chosen helper T-cell. When they bind together, interleukin secreted by the helper T-cell activated the Bcell and plasma, and memory cells are produced. Social gene 26 Primary and secondary response Those defenses can be divided into two stages: the primary response and secondary response. Primary response occurs when a foreign substance is encountered for the first time. The secondary response is the sequence that is triggered by the army of memory cells produced by the primary response. Social gene 27 Self-tolerance and autoimmunity All the cells of the body bear their own molecular "markers" embedded in their membranes. 所有的免疫細胞巡邏全身,只要有這些markers 的細胞,就不會攻擊。 This acceptance by the body's immune cells is called-tolerance. In some case, the immune system can turn against its own body, the reaction is called autoimmunity. Social gene 28 Interferon (干擾素) Interferon causes cells to become resistant to attacks by other viruses. It does not act against specific viruses but will inhibit any viral attack. Given interferon in a nasal spray 可以避免感冒。 Interferon reduced brain tumor size. Side effects: it triggers irregular heartbeats, it may also complicate liver or kidney problems. Social gene 29 Essay 20.3 How African crocodiles defend against Texan rabbits If you take hemoglobin from a rabbit and inject it into a crocodile, the crocodile will form antibodies against the rabbit hemoglobin. Why can this be? There are only about 300 DNA segments that code for the variable DNA segments of antibodies. Social gene 30 Recombination of DNA Only 300 DNA segments clearly not enough to provide an antibody response against every possible antigen. However, these regions are extremely unstable. They break apart and rejoin endlessly, providing a virtually infinite number of combinations (in humans, about 180億). Social gene 31 AIDS AIDS:acquired immuno-deficiency syndrome (後天免疫失調症候群) The first case of AIDS in the United States appeared in 1979, followed by a half-dozen cases reported in Los Angeles in 1981. In early 1989, the world Health Organization estimated that over one new case of AIDS was developing each minute, worldwide. Social gene 32 In 1995, it was reported between 63萬 and 89萬7千 人感染AIDS。 It is estimated that between 6 and 10 million people are presently affected with the virus but do not yet show symptoms. Many people carry antibodies to the virus that causes AIDS, showing that they have been exposed to it, without developing the symptoms. The syndrome, once full blown, is incurable and virtually always cause death within a few years (fewer than 14% of victims survive past three years). Social gene 33 Fig. 20.8 AIDS manifests itself in numerous ways, all marked by a deteriorating immune system. Early signs of AIDS include a series of lingering(慢性的), simple colds, night sweats, persistent fever, swollen glands, and coughing. More serious conditions follow, including at least three forms of cancer and destruction of the lungs and brain (Fig. 20.8) Social gene 34 Fig.20.9 AIDS is especially prevalent among needle-sharing addicts. Social gene 35 Dependence on condoms as a protection Some types of condoms are not completely effective. For example, those made of animal membranes, rather than rubber, do not block the passage of viruses. Also some men simply do not know how to use them safely.(The condom-sheathed penis must be withdrawn immediately after ejaculation). Social gene 36 The geographical source of HIV HIV(human immunodeficiency virus) 原本是在African green monkey (West Africa) 身體內的virus 轉入人體。 從西非傳至海地,美國同性戀者渡假地區。 再經由這些同性戀者,傳入美國。 然後,逐漸擴展至全球。 無論是同性或異性戀,都可以傳染。 Social gene 37 Essay 20.4 AIDS The infectious agent of AIDS was discovered in 1984. The virus is called HIV (human immunodeficiency virus). Social gene 38 HIV 攻擊 T-細胞 的過程。 Social gene 39 HIV 攻擊 T-細胞的過程。 The virus attacks the helper T-cell, penetrating the the cell and releasing a single strand of RNA and an enzyme, reverse transcriptase, with it. The enzyme enables the RNA to make a double strand of complementary DNA, which then joins the helper T-cell's DNA. Finally, there are so few helper T-cells in the blood that no effective immune response can be mounted against any attack whatsoever. Social gene 40 AIDS virus seeks out the helper T-cell lymphocytes. Using the various chemical markers on its surface, the AIDS virus binds easily to a receptor on the surface of the helper Tcell. Social gene 41 The HIV injects RNA and the enzyme transcriptase into T-cell. The enzyme helps transcribe the invading RNA into DNA. Once activated, the viral DNA directs the T-cell to make copies of the virus. Eventually the host cell dies. Social gene 42 問題與討論 http://mail.nutn.edu.tw/~hycheng Social gene 43