Selfish gene and sex selection 12-7-2015

Random X chromsome inactivation and Calico cat.

X Chromosome Inactivation XIC – X chromosome Inactivation Center XIC controls expression of the XIST gene XIST (X-inactive-specific transcript): a non-coding 17 kb RNA molecule “Coats” the entire local X-chromosome – cis-acting

Xist RNA-dependent and -independent silencing in mouse preimplantation embryos

X Chromosome Inactivation

XCI initiation varies in mammals Nat Rev Genet. 2014 June ; 15(6): 367–378

TSIX is the Anti-Sense Stand of the XIST gene

Long Noncoding RNAs May Alter Chromosome’s 3D Structure 24 MAY 2013 VOL 340 SCIENCE page 910

從複雜的個体、族群到生態圈 是競爭還是合作？

競爭：生命中無可逃避的宿命！ 食物 交配 陽光和水 But…..

生物為什會有利他的行為？ 合作的好處：互利互惠！ Wolves hunt in packs and then share their prey.

辨識與記憶能力是必要的條件避免白吃的揩油者！ Reciprocal altruism Vampire bats: sharing blood does have costs to the donor. But they may hope to get something back: the next night, they might miss out and the neighbor they fed will feed them in return (future benefits). 辨識與記憶能力是必要的條件避免白吃的揩油者！ 吃虧就是佔便宜！

當然不是！ 任何團体中都會有吃飯不作事的投機份子。 合作是生物世界中的常態嗎？ 當然不是！ 任何團体中都會有吃飯不作事的投機份子。

多細胞生物的源起：單個細胞合作的成果！

黏菌世界中的投機分子：只想成為孢子，而不願成為犧牲自已的支柱細胞！

生物世界如何對付投機分子？ 投機分子多半由於某些基因的損傷。 這些基因多半身負多重功能。 黏菌的投機分子單獨存在時，遇到惡劣環境往往無法正常發育分化成為孢子！ 此處得了便宜，它處必然得付出代價。

完美的利他主義者 Sterile workers in social insects: give up all reproduction for the benefit of their mother queen. 如何解釋這種完全利他的生命行為？

W.D. Hamilton (1936-2000)

Kin selection Hamilton’s Rule (1964) Relatedness to partner r.B > C Benefit to partner Personal cost This rule predicts when a gene for altruism should be selected. Prediction: cooperation at high relatedness, conflict at low relatedness.

Social insect: haploid male with diploid female X Sisters share genes via father OR mother, so average chance is 1 x 0.5 + 0.5 x 0.5 = 0.75 C AB 1 0.5 0,5 0,5 0,75 Worker generation AC BC AC BC

完美的利他主義者 如何解釋這種完全利他的生命行為？ 去幫助蟻后 (姐妹，R = 0.75)； 比照顧自已的後代 (R = 0.5) 更划算！

都是基因惹的禍:自私的基因！ Richard Dawkins: The Selfish Gene (1976) 為什要合作？ 都是基因惹的禍:自私的基因！ Richard Dawkins: The Selfish Gene (1976)

Parent birds feed their chick 無私的個人與自私的基因 Parent birds feed their chick

Altruistic donor individual Selfish “helping” gene 無私的行為源自於自私的基因！ Altruistic donor individual Selfish “helping” gene

身體是DNA的載具，它所有的作為都是在保存並散播DNA。 基因與個体間的関係 D N A Organism 在生殖的過程中完成複製. 身體是DNA的載具，它所有的作為都是在保存並散播DNA。

The idea of green-beard genes was invented by Hamilton , and named by Dawkins . How a gene can spread by recognizing and interacting with individuals carrying copies of itself? 1, to display an observable trait (the ‘green beard’); 2, to distinguish between individuals that do or do not display the trait; 3, to be altruistic to those that do.

Different alleles for Gp-9 locus (B and b) in fire ants influence whether workers will adopt (Bb) or kill queens (BB). Selfish genes: a green beard in the red fire ant. Nature 394, 573–575 (1998).

If the metaphor of selfish gene is right, Why sex reproduction is predominant in the world of eucaryotes (animal, plant and fungi)?

Sex: the greatest lottery on earth! George Bernard Shaw with actress. George Wald and Nobel sperm bank. Sickle cell anaemia how to keep one good and one bad gene together? Clone or sex reproduction?

Parthenogenesis

Why sex reproduction? Cost of finding a partner; Twofold cost of sex; Give a chance for the cheater (selfish gene); Syphilis, AIDS etc.

J. Proc. Linn. Soc. (Bot.), 6: 77-96; 1862. “We do not even in the least know the final cause of sexuality ; why new beings should be produced by the union of the two sexual element?” Darwin, C.R. On the two forms, or dimorphic condition, in the species Primual, and on their remarkable sexual relations. J. Proc. Linn. Soc. (Bot.), 6: 77-96; 1862.

A section of Darwin’s “notes on marriage”, 1838.

Emma Darwin in 1840

The Wedgwood and Darwin families Charles Darwin with his son William Erasmus in 1842

Key steps for sex reproduction: 1, Segregation of chromosomes; 2, Sister chromotid recombination and 3, Cell fusion

A key step in meiosis to make lots of different sex cells – crossing over! Crossing-over multiplies the already huge number of different gamete types produced by independent assortment.

How does sex reproduction arise? Sexual reproduction gene: option switch? You need genetic diversity to combat crisis (sex on). You also need to keep advantageous combinations of genes to remain intact (sex off). The sexy individuals were driving the evolution of sex reproduction Why no new cloner appear over billions of years?

Why asexuality fail? The good; From ab to Ab or aB to best survival AB Why sex is good! Nature 434: 571-2; 2005. The bad; Why sex? Science 311: 960-1; 2006. The ugly!

Low glucose; high temperature and high osmatic pressure (94 vs 80%)

Why asexuality fail? The bad; The ugly! 434: 571-2; 2005. Why sex? Science 311: 960-1; 2006. The ugly!

The water flea, Daphnia pulex, may shift from being sexual to being asexual and recombination in sexual cycle does lead to fewer deleterious mutations. . They observed a clear excess of nonsynonymous mutations in the asexual populations. They also estimated that close to 90% of the nonsynonymous mutations were subject to selection.

Why asexuality fail? The good; From ab to Ab or aB to best survival AB Why sex is good! Nature 434: 571-2; 2005. The bad; Why sex? Science 311: 960-1; 2006. The ugly! Conflict between host and parasite. Red queen theory 程樹德 ：紅皇后與有性生殖 (科學月刊 2011/05/13)

英國作家卡洛（Lewis Carroll）《愛麗絲鏡中奇遇》（Through the looking glass, and what Alice found there）裡，描寫小女孩愛麗絲在夢中變成棋子，與紅皇后博弈。紅皇后腳步疾行如風，但人卻總留在原地，落後於她的愛麗絲喘著大氣說：「在我們家鄉，您走得這麼快，肯定早不知走到那去了！」紅皇后說：「那是多慢的國度，在這你光是費勁跑，也只能留在原地。如果想到別的地方去，你至少得跑兩倍快才行！」

If host (H) and a parasite (p) to coevolve (top series of boxes), then high rates of sexual reproduction are sustained (graph, right). If frozen parasite stocks to reinfect each new generation of the host with a fixed, nonevolving ancestral strain of the parasite (p0 bottom series of boxes), rates of sexual reproduction can decline. Science 333: 166-7; 2011. When coevolving with parasites, all selfing C. elegans populations became extinct within 20 generations; but not sexual one!

Theory of Sexual Selection Darwin (1871, p256): “We are, however, here concerned only with that kind of selection, which I have called sexual selection. This depends on the advantage which certain individuals have over other individuals of the same sex and species, in exclusive relation to reproduction.”

Intersexual selection: The peacock’s tail Extravagant male ornaments The peacock’s tail greatly impairs his mobility…how could such a trait evolve?

Intrasexual Selection

Sexual Dimorphism

Why a theory of sexual selection? Darwin needed a theory to explain the many extravagant traits that seem to reduce survival e.g. the peacock’s tail

Fisher’s runaway model Fitness Tail length Total male fitness (survival + mating) Fitness due to survival Survival Selection Sexual Selection Female choice adaptive for survival

Brotherly love benefits females Nature 505: 626-7; 2014 Sexual competition between males may result in harm to females ( beetle, frog, fly). But what happy if males are brothers (kin selection)? Brotherly love benefits females Nature 505: 626-7; 2014

What happen is the males are AAB?

Sheep with big horn win the chance to mate!

Why not all the males have large horns?

Annual fitness variation and RXFP2 genotype. Life history trade-offs at a single locus maintain sexually selected genetic variation Nature  502, 93–95; 2013