{"id":15003,"date":"2016-08-01T14:39:51","date_gmt":"2016-08-01T11:39:51","guid":{"rendered":"http:\/\/109.232.216.219\/~bilimvegelecek\/?p=15003"},"modified":"2017-12-21T14:57:57","modified_gmt":"2017-12-21T11:57:57","slug":"darwin-devrimi-5-nihai-genetik-varyasyon-dna-duzeyi","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2016\/08\/01\/darwin-devrimi-5-nihai-genetik-varyasyon-dna-duzeyi","title":{"rendered":"Darwin devrimi \u2013 5: Nihai genetik varyasyon (DNA) d\u00fczeyi"},"content":{"rendered":"<p><em>DNA d\u00fczeyindeki genetik \u00e7e\u015fitlili\u011fi temel alan evrimsel genetik \u00e7al\u0131\u015fmalar\u0131n \u00f6nce tek tek \u201caday\u201d genler \u00fczerine odaklanan ve ard\u0131ndan genom d\u00fczeyindeki \u00e7e\u015fitlilik \u00fczerinden olas\u0131 t\u00fcrle\u015fme genlerinin saptanmas\u0131na dek uzanan geni\u015f bir kavray\u0131\u015f\u0131 ifade eden geli\u015fmeler son 20 y\u0131la damgas\u0131n\u0131 vurdu. <\/em><\/p>\n<p>Ge\u00e7en ayki yaz\u0131m\u0131zda proteinlerdeki amino asit yer de\u011fi\u015fimlerinin sonucu olarak ortaya \u00e7\u0131kabilen protein \u00e7e\u015fitlili\u011fi \u00fczerinden kavranan genetik \u00e7e\u015fitlili\u011fin evrimsel biyolojide yaratt\u0131\u011f\u0131 b\u00fcy\u00fck d\u00f6n\u00fc\u015f\u00fcm ve ivmelenmeden s\u00f6z etmi\u015ftik. Kendinden \u00f6nceki genetik \u00e7e\u015fitlilik tan\u0131mlama y\u00f6ntemlerini b\u00fcy\u00fck oranda g\u00f6lgede b\u0131rakan ve Kuhnvari bir paradigma de\u011fi\u015fimine yol a\u00e7an allozim elektroforezi y\u00f6ntemi, bununla birlikte, i\u00e7erdi\u011fi teknik k\u0131s\u0131tlamalar dolay\u0131s\u0131yla, bir t\u00fcr\u00fcn sahip oldu\u011fu genetik \u00e7e\u015fitlilik miktar\u0131n\u0131n ancak belirli bir b\u00f6l\u00fcm\u00fcn\u00fc ortaya koyabilmekteydi. Bu tekni\u011fin kullan\u0131lmaya ba\u015flad\u0131\u011f\u0131 d\u00f6nemlerden bu yana bilinen ve \u00f6zellikle se\u00e7ilimci-n\u00f6tral evrimci kutupla\u015fma d\u00e2hilinde iyice kronikle\u015fen bu sorunun, DNA d\u00fczeyindeki ve dolay\u0131s\u0131yla nihai durumdaki genetik varyasyonun saptanabilmesiyle a\u015f\u0131labilece\u011fi de ara\u015ft\u0131r\u0131c\u0131larca hep a\u00e7\u0131k \u015fekilde kavranmaktayd\u0131. Bir gendeki Protein elektroforezi ile saptanabilen farkl\u0131 form (alel) say\u0131s\u0131n\u0131 art\u0131rabilen kimyasal m\u00fcdahaleler (\u00f6rne\u011fin, farkl\u0131 y\u00fcr\u00fctme tamponlar\u0131, s\u0131cakl\u0131k ve iyon konsantrasyon d\u00fczeyleri) sonucunda belirli bir a\u015fama kaydedilmesine kar\u015f\u0131n, protein d\u00fczeyindeki farkl\u0131 form say\u0131s\u0131n\u0131n art\u0131\u015f\u0131n\u0131n DNA\u2019daki daha \u00e7ok say\u0131daki farkl\u0131l\u0131\u011f\u0131n i\u015fareti olabilece\u011finin anla\u015f\u0131lmas\u0131<sup>1<\/sup>, genetik \u00e7e\u015fitlili\u011fi DNA seviyesinde ifade etmenin birincil \u00f6nemine i\u015faret etmekteydi.<\/p>\n<p>Bu sorunun a\u015f\u0131lmas\u0131na ili\u015fkin ilk i\u015faretleri 1970\u2019lerin sonlar\u0131na do\u011fru DNA dizilenme y\u00f6nteminin ke\u015ffi vermekteydi.<sup>2<\/sup> DNA dizilenmesinin yaratt\u0131\u011f\u0131 b\u00fcy\u00fck d\u00f6n\u00fc\u015f\u00fcm\u00fcn, temel sorunsal\u0131 genetik varyasyon \u00fczerine in\u015fa edilmi\u015f evrimsel biyolojiye yans\u0131mamas\u0131 elbette beklenemezdi ve nitekim DNA dizisi \u00fczerinden bir gendeki genetik \u00e7e\u015fitlili\u011fi b\u00fct\u00fcn y\u00fczleri ile ele alan ilk \u00e7al\u0131\u015fma <em>Drosophila melanogaster<\/em>\u2019deki,\u00a0 evrimsel geneti\u011fin bir locus classicus\u2019u haline gelmi\u015f olan <em>Adh<\/em> (alkol dehidrogenaz) genindeki varyasyona odaklanmaktayd\u0131.<sup>3<\/sup><\/p>\n<p>Alkol dehidrogenaz geni, <em>D. melanogaster<\/em>\u2019in do\u011fal ortam\u0131nda yer alan alkol\u00fcn par\u00e7alanmas\u0131nda ve enerji metabolizmas\u0131nda kullan\u0131lmas\u0131na olanak veren anahtar genlerden biriydi ve protein elektroforeziyla tan\u0131mlanan iki yayg\u0131n forma sahipti. Bu formlar\u0131n aras\u0131ndaki tek bir amino asit fark\u0131ndan kaynaklanan biyokimyasal ve fizyolojik farklar\u0131n, bu formlar\u0131n be\u015f k\u0131tadaki benzer da\u011f\u0131l\u0131m \u00f6r\u00fcnt\u00fclerini izah edebildi\u011fi d\u00fc\u015f\u00fcn\u00fclmesine kar\u015f\u0131n<sup>4<\/sup>, <em>Adh<\/em> geninin di\u011fer kimi gen ve kromozom \u00e7e\u015fitlilik bi\u00e7imleriyle olan ili\u015fkisi, da\u011f\u0131l\u0131m \u00f6r\u00fcnt\u00fcs\u00fc alt\u0131nda yatan nedenlerin sadece bu gendeki farkl\u0131l\u0131klardan kaynaklanmayabilece\u011fine de i\u015faret etmekteydi.<sup>5<\/sup><\/p>\n<p>Nitekim Martin Kreitman\u2019\u0131n yukarda an\u0131lan ve <em>Adh<\/em> genini model alan, DNA d\u00fczeyindeki ilk evrimsel genetik analizi, sadece tek bir gen d\u00fczeyinde bile hik\u00e2yenin olduk\u00e7a karma\u015f\u0131k bir hal alabilece\u011fini g\u00f6stermekteydi: \u00d6rne\u011fin, elektroforetik olarak ayr\u0131labilen protein d\u00fczeyinde, yek bir amino asit fark\u0131ndan kaynaklanan iki genetik form bulunmas\u0131na kar\u015f\u0131n, bu formlardan her biri kendi i\u00e7inde n\u00fckleotid bazlar\u0131 a\u00e7\u0131s\u0131ndan \u00e7e\u015fitlilik g\u00f6stermekteydi. Her iki elektroforetik form toplamda 43 baz \u00e7ifti noktas\u0131 bak\u0131m\u0131ndan farkl\u0131yd\u0131! Ayr\u0131ca, sadece baz \u00e7ifti yer de\u011fi\u015ftirmelerinden kaynaklanmayan, g\u00f6rece az say\u0131da da olsa, <em>Adh<\/em> genine hareketli genetik elementlerin girip \u00e7\u0131kt\u0131\u011f\u0131na i\u015faret eden baz fazlal\u0131klar\u0131 ve eksilmeleri de mevcuttu. Daha da \u00f6nemlisi, genin protein yap\u0131s\u0131na amino asit sa\u011flayan b\u00f6lgeleri ile sa\u011flamayan b\u00f6lgeleri aras\u0131nda, do\u011fal se\u00e7ilimin varl\u0131\u011f\u0131na i\u015faret eder \u015fekilde, bariz genetik \u00e7e\u015fitlilik farklar\u0131 bulunuyordu. Hepsinden \u00f6nemlisi, protein seviyesinde sadece iki farkl\u0131 formla do\u011fal olarak temsil edilen genin DNA seviyesindeki bu son derece artm\u0131\u015f \u00e7e\u015fitlili\u011fi, co\u011frafi olarak farkl\u0131 pop\u00fclasyonlardan gelme <em>Adh<\/em> formlar\u0131 i\u00e7inde saptanm\u0131\u015ft\u0131. Bir ba\u015fka deyi\u015fle, DNA d\u00fczeyindeki \u00e7e\u015fitlili\u011fi co\u011frafi etkenler \u00e7er\u00e7evesinde ya da co\u011frafi b\u00f6l\u00fcmlenmenin yaratt\u0131\u011f\u0131 nedenler d\u00e2hilinde a\u00e7\u0131klaman\u0131n m\u00fcmk\u00fcn olaca\u011f\u0131 g\u00f6r\u00fcl\u00fcyordu.<\/p>\n<p>Evrimsel geneti\u011fin DNA dizisi ile ilk temas\u0131 diyebilece\u011fimiz bu \u00e7al\u0131\u015fma, do\u011fal pop\u00fclasyonlardaki nihai genetik \u00e7e\u015fitlilik miktar\u0131n\u0131n da\u011f\u0131l\u0131m\u0131 ve bu da\u011f\u0131l\u0131m\u0131n nedenleri hakk\u0131nda fikir verebilecek parametrelerin hesaplanmas\u0131n\u0131 da m\u00fcmk\u00fcn k\u0131lmaktayd\u0131. Nitekim DNA seviyesindeki \u00e7e\u015fitlilik miktar\u0131 ile bu \u00e7e\u015fitlili\u011fin da\u011f\u0131l\u0131m\u0131 aras\u0131ndaki ili\u015fkiyi do\u011fal se\u00e7ilimin varl\u0131\u011f\u0131n\u0131n ara\u015ft\u0131r\u0131lmas\u0131 ba\u011flam\u0131nda istatistiksel bir test ile tan\u0131mlayan kuramsal \u00e7er\u00e7evenin <em>Adh<\/em> ve benzer genetik dizi analizlerini takiben ortaya konmu\u015f olmas\u0131 da \u015fa\u015f\u0131rt\u0131c\u0131 de\u011fildir.<sup>6,7<\/sup> Yine, adaptif protein evrimi konusundaki ilk yakla\u015f\u0131m\u0131n ve test arg\u00fcman\u0131n\u0131n <em>Drosophila melanogaster<\/em> ve ona yak\u0131n akraba t\u00fcrlerdeki <em>Adh<\/em> DNA dizisi kar\u015f\u0131la\u015ft\u0131r\u0131lmalar\u0131 \u00fczerinden tan\u0131mland\u0131\u011f\u0131n\u0131 da ge\u00e7meden s\u00f6yleyelim.<sup>8<\/sup><\/p>\n<p>Uzun y\u0131llar boyunca hem protein \u00e7e\u015fitlili\u011fi hem de bu \u00e7e\u015fitlili\u011fi bi\u00e7imlendiren co\u011frafi ve iklimsel, biyokimyasal ve fizyolojik parametreler \u00e7er\u00e7evesinde evrimsel biyolojinin \u00f6nemli modellerinden biri olmu\u015f <em>Drosophila Adh<\/em> genindeki nihai (DNA) genetik \u00e7e\u015fitlili\u011fin t\u00fcm y\u00f6nleriyle saptand\u0131\u011f\u0131 bu \u00e7al\u0131\u015fma, sonraki benzeri \u00e7al\u0131\u015fmalara esin kayna\u011f\u0131 olmu\u015f ve b\u00fct\u00fcn t\u00fcrlere uygulanabilen temel bir tak\u0131m istatistiksel yakla\u015f\u0131mlar\u0131n ortaya \u00e7\u0131kmas\u0131n\u0131 da te\u015fvik etmi\u015ftir. DNA seviyesinde saptanan, genin i\u015fleve d\u00f6n\u00fc\u015fen-d\u00f6n\u00fc\u015fmeyen t\u00fcm k\u0131s\u0131mlar\u0131ndaki genetik \u00e7e\u015fitlili\u011fin, t\u00fcr-i\u00e7i evrimsel de\u011fi\u015fimler hakk\u0131nda sa\u011flad\u0131\u011f\u0131 ola\u011fan\u00fcst\u00fc bilgi derinli\u011finin yan\u0131 s\u0131ra, ayn\u0131 ya da farkl\u0131 co\u011frafyalarda ya\u015fayan, aralar\u0131nda belli derecelerde akrabal\u0131k ili\u015fkileri bulunan farkl\u0131la\u015fm\u0131\u015f taksonomik birimlerin farkl\u0131la\u015fma dereceleri hakk\u0131nda bilgi vermesi ve hatta bu farkl\u0131la\u015fmalar\u0131n ad\u0131na t\u00fcr dedi\u011fimiz, b\u00fcy\u00fck oranda yal\u0131t\u0131k ve kesintili varl\u0131klar \u015feklinde organizasyonunun izah\u0131 bak\u0131m\u0131ndan anlamland\u0131r\u0131lmas\u0131 da ka\u00e7\u0131n\u0131lmazd\u0131.<\/p>\n<p>Sonu\u00e7 itibar\u0131yla, DNA d\u00fczeyindeki genetik \u00e7e\u015fitlili\u011fi temel alan evrimsel genetik \u00e7al\u0131\u015fmalar\u0131n \u00f6nce tek tek \u201caday\u201d genler \u00fczerine odaklanan ve ard\u0131ndan genom d\u00fczeyindeki \u00e7e\u015fitlilik \u00fczerinden olas\u0131 t\u00fcrle\u015fme genlerinin saptanmas\u0131na dek uzanan geni\u015f bir kavray\u0131\u015f\u0131 ifade eden geli\u015fmeler son 20 y\u0131la damgas\u0131n\u0131 vurmu\u015f durumdad\u0131r.<\/p>\n<p>Yaz\u0131m\u0131z\u0131n \u00f6n\u00fcm\u00fczdeki ayki konusu, t\u00fcrle\u015fme geneti\u011fi ve genomu \u00fczerine yap\u0131lan \u00f6rnek \u00e7al\u0131\u015fmalara odaklanacak. \u00d6n\u00fcm\u00fczdeki ay, Darwin\u2019den bu yana yap\u0131lan say\u0131s\u0131z ara\u015ft\u0131rmaya konu olmu\u015f do\u011fal bir laboratuvar konumundaki Galapagoslar\u2019daki Darwin ispinozlar\u0131 ve t\u00fcrle\u015fmelerine bakaca\u011f\u0131z. Ayr\u0131ca, yine en \u00f6nemli t\u00fcrle\u015fme modellerinden birini veren Do\u011fu Afrika\u2019daki krater g\u00f6l sistemindeki cichlid bal\u0131klar\u0131ndaki farkl\u0131 t\u00fcrlerin olu\u015fumuna varan evrimsel de\u011fi\u015fimleri DNA d\u00fczeyinden ele alan \u00e7ok yak\u0131n tarihli genomik bir ara\u015ft\u0131rman\u0131n sonu\u00e7lar\u0131n\u0131 \u00f6zetleyece\u011fiz. B\u00f6ylece, Darwin devrimini \u00e7ok \u00f6zet bi\u00e7imiyle konu edinen dizimizin de sonuna gelmi\u015f olaca\u011f\u0131z.<\/p>\n<p><strong>Kaynaklar<\/strong><\/p>\n<p>1) Antonio Barbadilla, Lynn M. King ve Richard C. Lewontin, 1996. What Does Electrophoretic Variation Tell Us About Protein Variation? <em>Mol. Biol. Evol<\/em>. 13: 427-432.<\/p>\n<p>2) F. Sanger, S. Nicklen ve A. R. Coulson, 1977. DNA sequencing with chain-terminating inhibitors. <em>PNAS<\/em> 74: 5463-5467.<\/p>\n<p>3) Martin Kreitman, 1983. Nucleotide polymorphism at the alcohol dehydrogenase locus of <em>Drosophila melanogaster<\/em>.<em> Nature<\/em> 304: 412-417.<\/p>\n<p>4) Wilke van Delden, 1982. The alcohol dehydrogenase polymorphism in <em>Drosophila melanogaster<\/em>: Selection at an ezyme locus. Evol. Biol. 15: 187-222.<\/p>\n<p>5) Wilke van Delden ve A. Kamping, 1989. The association between the polymorphisms at the <em>Adh<\/em> and <em>\u03b1Gpdh<\/em> loci and the <em>In(2L)t<\/em> inversion in <em>Drosophila melanogaster<\/em> in relation to temperature<em>. Evolution<\/em> 43: 775-793.<\/p>\n<p>6) Fumio Tajima, 1989. Statistical Method for Testing the Neutral Mutation Hypothesis by DNA Polymorphism<em>. Genetics<\/em> 123: 585-595<strong>.<\/strong><\/p>\n<p>7) Yun-Xin Fu\u2019 ve Wen-Hsiung Li, 1993. Statistical Tests of Neutrality of Mutations. <em>Genetics<\/em> 133: 693-709.<\/p>\n<p>8) John. M. NcDonald ve Martin Kreitman, 1991. Adaptive protein evolution at the Adh locus in Drosophila.<em> Nature<\/em> 351: 652-654.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>DNA d\u00fczeyindeki genetik \u00e7e\u015fitlili\u011fi temel alan evrimsel genetik \u00e7al\u0131\u015fmalar\u0131n \u00f6nce tek tek \u201caday\u201d genler \u00fczerine odaklanan ve ard\u0131ndan genom d\u00fczeyindeki \u00e7e\u015fitlilik \u00fczerinden olas\u0131 t\u00fcrle\u015fme genlerinin saptanmas\u0131na dek uzanan geni\u015f bir kavray\u0131\u015f\u0131 ifade eden geli\u015fmeler son 20 y\u0131la damgas\u0131n\u0131 vurdu. Ge\u00e7en ayki yaz\u0131m\u0131zda proteinlerdeki amino asit yer de\u011fi\u015fimlerinin sonucu olarak ortaya \u00e7\u0131kabilen protein \u00e7e\u015fitlili\u011fi \u00fczerinden kavranan [&hellip;]<\/p>\n","protected":false},"author":67,"featured_media":15004,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[187,1475,21,32,231],"tags":[461,272,200,431,292,525],"class_list":["post-15003","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-150-sayi","category-bilim-ve-tarih","category-biyoloji","category-evrim","category-molekuler-biyoloji-ve-genetik","tag-darwin","tag-dna","tag-evrim","tag-gen","tag-genetik","tag-kromozom"],"acf":[],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/15003","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/users\/67"}],"replies":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/comments?post=15003"}],"version-history":[{"count":0,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/posts\/15003\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media\/15004"}],"wp:attachment":[{"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/media?parent=15003"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/categories?post=15003"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bilimvegelecek.com.tr\/index.php\/wp-json\/wp\/v2\/tags?post=15003"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}