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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
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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
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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)
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12.1 Introduction
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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。
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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。
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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.
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12.2 Genes as strategists
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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。
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12.3 Variant genes
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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
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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.
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12.4 The reach of the strategic gene
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Dawkins (1976) a thought-experiment
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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.
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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.
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12.5 The prokaryotic firm: managing
a cytoplasmic commons
原核公司：經營細胞質公共財
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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.
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Thus, genetic communities are potentially vulnerable
to free-riders, genes that take more than they
contribute.
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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.
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12.6 Dangerous liaisons (聯繫)
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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.
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細菌的plasmid 通常是一些特別的 metabolic
skills. 譬如：antibiotic resistance
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於細菌交接的過程，通常只有plasmid傳送。
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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。
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12.7 Plasmid protection rackets
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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.
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Mitochondria
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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?
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If so, one would predict that minicircles can also edit
DNS and encrypt maxicircle genes in ways that only
they can decipher (解讀).
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12.8 Team substitutions (換組员)
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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)
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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).
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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)
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12.9 Multicellular corporations
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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).
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多細胞公司
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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)
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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。
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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)
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Specific responses
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Two kinds of lymphocytes play a critical role
in the specific responses.
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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。
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cellular immunity
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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.
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抗原-抗體反應
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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.
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Fig. 20.4
巨喫細胞
Fig. 20.5
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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.
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Fig. 20.6 In the ongoing
combat against
invaders.
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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.
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Fig. 20.7
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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.
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Primary and secondary
response
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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.
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Self-tolerance and
autoimmunity
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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.
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Interferon (干擾素)
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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.
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Essay 20.3 How African crocodiles
defend against Texan rabbits
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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.
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Recombination of DNA
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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).
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AIDS
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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.
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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).
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Fig. 20.8 AIDS manifests
itself in numerous ways,
all marked by a
deteriorating immune
system.
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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)
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Fig.20.9 AIDS is especially prevalent among
needle-sharing addicts.
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Dependence on condoms as a
protection
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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).
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The geographical source of
HIV
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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。
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Essay 20.4
AIDS
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The infectious
agent of AIDS
was discovered
in 1984.
The virus is
called HIV
(human
immunodeficiency virus).
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HIV 攻擊 T-細胞
的過程。
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HIV 攻擊 T-細胞的過程。
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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.
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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.
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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.
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問題與討論
http://mail.nutn.edu.tw/~hycheng
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