{"id":15664,"date":"2016-05-01T12:51:44","date_gmt":"2016-05-01T09:51:44","guid":{"rendered":"http:\/\/109.232.216.219\/~bilimvegelecek\/?p=15664"},"modified":"2018-01-03T12:59:56","modified_gmt":"2018-01-03T09:59:56","slug":"darwin-devrimi-2-evrimsel-genetigin-kurucu-babalari","status":"publish","type":"post","link":"https:\/\/bilimvegelecek.com.tr\/index.php\/2016\/05\/01\/darwin-devrimi-2-evrimsel-genetigin-kurucu-babalari","title":{"rendered":"Darwin devrimi – 2:\u00a0Evrimsel geneti\u011fin kurucu babalar\u0131"},"content":{"rendered":"

Ronald A. Fisher, JBS Haldane ve Sewall Wright. Evrimsel geneti\u011fin bu \u00fc\u00e7 kurucu babas\u0131 da, temelinde se\u00e7ilimle evrimle\u015fmenin yer ald\u0131\u011f\u0131 Darwinci evrimsel biyolojinin toparlan\u0131\u015f\u0131, yeniden bi\u00e7imleni\u015fi ve \u201cModern Sentez\u201de giden yolu d\u00f6\u015feyen ta\u015flar\u0131n olu\u015fturulmas\u0131 bak\u0131m\u0131ndan b\u00fcy\u00fck \u00f6neme sahiptir.<\/em><\/p>\n

Ge\u00e7en yaz\u0131m\u0131zda, Charles Darwin\u2019in evrimsel biyoloji bilimini do\u011furup \u015fekillendiren devrimci etkisinin, K\u00f6ken<\/em>\u2019de \u00f6nceki benzerleriyle k\u0131yaslanamayacak \u00f6l\u00e7\u00fcde ayr\u0131nt\u0131l\u0131 ve tutarl\u0131 \u015fekilde ortaya koydu\u011fu do\u011fal se\u00e7ilimle ortak bir k\u00f6kenden t\u00fcreme olmad\u0131\u011f\u0131n\u0131, ideal tipler \u015feklinde bin y\u0131l\u0131 a\u015fk\u0131n s\u00fcredir Bat\u0131 zihninde k\u00f6klenen t\u00fcrlerin de\u011fi\u015fmezli\u011fi alg\u0131s\u0131n\u0131, t\u00fcrlerin bireylerinde g\u00f6r\u00fclen biyolojik de\u011fi\u015fkenli\u011fi kullanarak tepetaklak etmesi oldu\u011funu s\u00f6ylemi\u015ftik. Aralar\u0131nda ge\u00e7i\u015f olmayan anl\u0131k yarat\u0131l\u0131\u015f \u00fcr\u00fcnleri olarak kabul edilen t\u00fcrler, akrabal\u0131k ili\u015fkisine ve bu ili\u015fkinin do\u011fal s\u00fcre\u00e7lerle kurulmas\u0131na olanak veren \u201cdejenere\u201d biyolojik de\u011fi\u015fkenli\u011fe yap\u0131lan vurguyla\u00a0 evrimsel s\u00fcrecin normal par\u00e7alar\u0131 haline gelmi\u015flerdi zihniyet d\u00fcnyas\u0131nda.<\/p>\n

Yaz\u0131m\u0131z\u0131n bu b\u00f6l\u00fcm\u00fcnde ise, Darwin\u2019den bu yana kal\u0131t\u0131msal biyolojik de\u011fi\u015fkenlik odakl\u0131 evrimsel biyolojinin tarihsel \u00e7izgilerini genel itibar\u0131yla takip etmeye devam edece\u011fiz. Yaz\u0131m\u0131z\u0131n sonraki ve son b\u00f6l\u00fcm\u00fcnde ise tarihsel perspektifi \u00f6zetlemeye devam edecek ve genom \u00e7e\u015fitlili\u011fi odakl\u0131 g\u00fcncel t\u00fcrle\u015fme \u00e7al\u0131\u015fmalar\u0131 \u00fczerinde duraca\u011f\u0131z. B\u00f6ylece, Darwinci evrimsel biyolojinin ta\u00e7land\u0131\u011f\u0131 g\u00fcn\u00fcm\u00fcz evrimsel biyoloji disiplininin vard\u0131\u011f\u0131 nokta hakk\u0131nda bir fikir olu\u015fturmaya \u00e7al\u0131\u015faca\u011f\u0131z.<\/p>\n

Mendel\u2019in yeniden ke\u015ffi ve t\u0131kan\u0131kl\u0131\u011f\u0131n a\u015f\u0131lmas\u0131<\/strong><\/p>\n

\u00d6ncelikle, K\u00f6ken<\/em>\u2019in 1859\u2019da yay\u0131nlanmas\u0131n\u0131 takiben b\u00fcy\u00fck ilgi \u00e7ekti\u011fi ve f\u0131rt\u0131nalar kopard\u0131\u011f\u0131n\u0131 \u015feklindeki do\u011fru ve ancak iyice s\u0131radanla\u015fm\u0131\u015f tespitin \u00fcst\u00fcnde durmadan, do\u011fal se\u00e7ilimle evrimle\u015fme \u015feklinde \u00f6zetleyebilece\u011fimiz Darwinci evrimsel biyolojinin 19. y\u00fczy\u0131l sonlar\u0131na do\u011fru g\u00f6r\u00fcl\u00fcr bir kan kayb\u0131 ya\u015famaya ba\u015flad\u0131\u011f\u0131n\u0131 hemen belirtelim. D\u00f6nemin jeolojik kay\u0131tlar\u0131ndan \u00e7\u0131kan ve ya\u015famakta olan t\u00fcrlerle kurulan benzerlik ili\u015fkileri ve anatomik ve morfolojik kar\u015f\u0131la\u015ft\u0131rmalarla detayland\u0131r\u0131lan bu ili\u015fkilerin biyoco\u011frafya bak\u0131m\u0131ndan takibinde ortak k\u00f6ken ili\u015fkileri b\u00fcy\u00fck kolayl\u0131k sa\u011flamas\u0131na yani Darwin\u2019in ortak k\u00f6ken tespitinin b\u00fcy\u00fck oranda kabul\u00fcne ra\u011fmen, t\u00fcrlerin yok olu\u015fu ve yeni t\u00fcrlerin ortaya \u00e7\u0131k\u0131\u015f\u0131n\u0131 t\u00fcr i\u00e7indeki de\u011fi\u015fkenli\u011fin do\u011fal se\u00e7ilimle olan tarihsel etkile\u015fimine ba\u011flayan sac aya\u011f\u0131 hayli sars\u0131lm\u0131\u015f durumdayd\u0131. Bir ba\u015fka deyi\u015fle, t\u00fcr i\u00e7i de\u011fi\u015fkenli\u011fin se\u00e7ilimle yo\u011frulmas\u0131 diyebilece\u011fimiz evrimle\u015fme s\u00fcrecini ortaya koyman\u0131n d\u00f6nem i\u00e7in s\u00f6z konusu olan ola\u011fan\u00fcst\u00fc g\u00fc\u00e7l\u00fc\u011f\u00fc, do\u011fal se\u00e7ilimin laftan ibaret bir kurgu oldu\u011fu \u015feklindeki alg\u0131y\u0131 g\u00fc\u00e7lendirmekteydi.<\/p>\n

19. y\u00fczy\u0131l sonlar\u0131 ile 20. y\u00fczy\u0131l\u0131n ilk \u00e7eyre\u011finde net bi\u00e7imde g\u00f6rebilece\u011fimiz bu t\u0131kan\u0131kl\u0131k durumu, a\u015f\u0131lmas\u0131 g\u00fc\u00e7 ve se\u00e7ilim kar\u015f\u0131t\u0131 ve Darwin\u2019in hesapla\u015f\u0131p geride b\u0131rakt\u0131\u011f\u0131na ikna oldu\u011fu teolojik ve teleolojik alternatiflerin yeniden ve daha sofistike bi\u00e7imde dillendirildi\u011fi bir \u201ckaranl\u0131k devir\u201ddir adeta.1<\/sup> Bu d\u00f6nemin atlat\u0131lmas\u0131n\u0131n devindirici motoru ise, hi\u00e7 ku\u015fkusuz, ayr\u0131nt\u0131lar\u0131n\u0131 ba\u015fka bir yaz\u0131ya b\u0131rakaca\u011f\u0131m\u0131z, Mendel\u2019in yeniden ke\u015ffi denen ve yakla\u015f\u0131k 40 y\u0131ld\u0131r yayg\u0131nla\u015fmay\u0131 bekleyen temel genetik ilkelerinin ba\u011f\u0131ms\u0131z \u00e7al\u0131\u015fmalarla ortaya konmas\u0131yla b\u00fct\u00fcn biyoloji ve yan disiplinlerin gidi\u015fat\u0131n\u0131 k\u00f6kten de\u011fi\u015ftiren hadiseler toplam\u0131d\u0131r.<\/p>\n

Konumuz itibar\u0131yla \u00f6zetle s\u00f6ylersek, Mendel ilkeleri \u0131\u015f\u0131\u011f\u0131nda, mayoz b\u00f6l\u00fcnmenin basit sonu\u00e7lar\u0131 olan e\u015fey h\u00fccresi s\u0131kl\u0131klar\u0131n\u0131n e\u015fle\u015fme s\u0131kl\u0131\u011f\u0131 \u015feklinde d\u00fczenlenmesi ve e\u015fle\u015fme oranlar\u0131n\u0131n de\u011fi\u015fmeden devam\u0131na dayal\u0131 bir evrimsel dura\u011fanl\u0131\u011f\u0131n, konuyu matematiksel netli\u011fi i\u00e7inde ba\u011f\u0131ms\u0131z olarak ele alan biliminsanlar\u0131n\u0131n adlar\u0131n\u0131 zikrederek, me\u015fhur Hardy-Weinberg dengesi \u015feklinde ifade edilmesi bir d\u00f6n\u00fcm noktas\u0131 olmu\u015ftur. Bu dura\u011fanl\u0131k modeli, evrimsel de\u011fi\u015fmezli\u011fi genetik de\u011fi\u015fkenli\u011fi tan\u0131mlayan alternatif genetik formlar\u0131n, Mendel\u2019in \u00e7iftler \u015feklinde (biri anneden di\u011feri babadan) bulundu\u011funu ke\u015ffetti\u011fi kal\u0131t\u0131msal birim fakt\u00f6rlerin s\u0131kl\u0131klar\u0131n\u0131n de\u011fi\u015fmezli\u011fine dayand\u0131ran, fizik ve kimyan\u0131n ideal gaz denklemine benzer bir \u00e7\u0131k\u0131\u015f noktas\u0131 te\u015fkil etmektedir.<\/p>\n

\u00dc\u00e7 kurucu baba<\/strong><\/p>\n

Bu dura\u011fanl\u0131k modelini do\u011fal se\u00e7ilimin genetik kuram\u0131n\u0131 ortaya koymak i\u00e7in kullanan ki\u015fi ise b\u00fcy\u00fck istatistik\u00e7i, varyans analizinin mucidi ve pop\u00fclasyon geneti\u011finin \u00fc\u00e7 kurucu babas\u0131ndan biri kabul edilen Ronald Aylmer Fisher\u2019dir. Fisher, insan do\u011fum ve \u00f6l\u00fcm oranlar\u0131n\u0131 kullanarak, Mendel geneti\u011finin ilkeleri \u00e7er\u00e7evesinde, Hardy-Weinberg dengesinden sapmalar \u015feklinde do\u011fal se\u00e7ilimin matematiksel tarifini yapar.2<\/sup> Fisher\u2019in do\u011fal se\u00e7ilimi g\u00f6sterdi\u011fi matematiksel pop\u00fclasyon genetik yakla\u015f\u0131m\u0131 ve t\u00fcrevleri, vazge\u00e7ilmez bir se\u00e7ilimle evrimle\u015fme modeli olarak g\u00fcn\u00fcm\u00fcz evrimsel biyoloji literat\u00fcr\u00fcndeki \u00f6nemli yerini korumaktad\u0131r (Fisher\u2019in 19. y\u00fczy\u0131l sonlar\u0131nda alevlenen, 20. y\u00fczy\u0131l ba\u015flar\u0131nda nihayete eren ve kantitatif geneti\u011fin do\u011fmas\u0131na yol a\u00e7an biyometrici-Mendelci kal\u0131t\u0131m kavgas\u0131n\u0131n sonlanmas\u0131ndaki pay\u0131 da b\u00fcy\u00fckt\u00fcr. Bu konuyu da sonraya b\u0131rakal\u0131m).<\/p>\n

Fisher\u2019le hemen ayn\u0131 y\u0131llarda, b\u00fcy\u00fck alim ve velut John Burden Sanderson Haldane, Fisher\u2019in izinde, se\u00e7ilim katsay\u0131lar\u0131na ili\u015fkin diferansiyelleri veren \u00f6nemli \u00e7al\u0131\u015fmalar\u0131n\u0131 ortaya koymaktad\u0131r.3<\/sup> Fisher ve Haldane\u2019nin ortaya koydu\u011fu \u00e7er\u00e7eve, genel itibar\u0131yla, uyum ba\u015far\u0131s\u0131 giderek artan bir t\u00fcre ait pop\u00fclasyonlar\u0131n do\u011fal se\u00e7ilimle, bir genin farkl\u0131 formlar\u0131n\u0131n olu\u015fturdu\u011fu genotiplerin -kabaca s\u00f6ylersek- bir sonraki ku\u015fa\u011fa yavru d\u00f6l aktarma d\u00fczeylerinin fonksiyonu \u015feklinde ifade edilen uyum ba\u015far\u0131s\u0131 farklar\u0131n\u0131n sonucunda, bir t\u00fcre ait pop\u00fclasyonlar\u0131n giderek b\u00fcy\u00fcmesini \u00f6ng\u00f6ren dinamik bir modeli tarif etmektedir.<\/p>\n

Ancak yine hemen ayn\u0131 d\u00f6nemlerde, Amerikal\u0131 b\u00fcy\u00fck teorik pop\u00fclasyon genetik\u00e7isi Sewall Wright, do\u011fal se\u00e7ilimle pop\u00fclasyon b\u00fcy\u00fckl\u00fc\u011f\u00fcn\u00fc bir arada ele alan, g\u00f6rece daha ger\u00e7ek\u00e7i bir modeli ortaya atm\u0131\u015ft\u0131r. Wright\u2019\u0131n yakla\u015f\u0131m\u0131yla, gen s\u0131kl\u0131klar\u0131ndaki rasgele olan-olmayan de\u011fi\u015fimlerin pop\u00fclasyon b\u00fcy\u00fckl\u00fc\u011f\u00fc ile ele al\u0131nmas\u0131 ve mutasyon, gen ak\u0131\u015f\u0131 gibi di\u011fer \u00f6nemli evrim s\u00fcre\u00e7lerinin hesaba kat\u0131lmas\u0131, se\u00e7ilimle evrimle\u015fmeye ili\u015fkin resmin hatlar\u0131n\u0131 iyice ortaya \u00e7\u0131karmaktad\u0131r.4<\/sup><\/p>\n

Aralar\u0131ndaki kimi farklara kar\u015f\u0131n, evrimsel geneti\u011fin bu \u00fc\u00e7 kurucu babas\u0131 da, temelinde se\u00e7ilimle evrimle\u015fmenin yer ald\u0131\u011f\u0131 Darwinci evrimsel biyolojinin 20. y\u00fczy\u0131ldaki toparlan\u0131\u015f\u0131, sa\u011flam \u015fekilde yeniden bi\u00e7imleni\u015fi ve \u201cModern Sentez\u201de giden yolu d\u00f6\u015feyen ta\u015flar\u0131n olu\u015fturulmas\u0131 bak\u0131m\u0131ndan b\u00fcy\u00fck \u00f6neme sahiptir. Onlar\u0131n sayesinde, genetik temelli biyolojik \u00f6zellik de\u011fi\u015fkenli\u011finin dinamik do\u011fal se\u00e7ilim s\u00fcreciyle evrimle\u015fmeyi sa\u011flamas\u0131na ili\u015fkin en temel yakla\u015f\u0131mlar olu\u015fturulmu\u015f ve modern evrimsel biyolojinin genetik omurgas\u0131 yerine oturtulmu\u015ftur.<\/p>\n

\u2018Sinek odas\u0131\u2019<\/strong><\/p>\n

Yine ayn\u0131 d\u00f6nemlerde, Amerikal\u0131 genetik\u00e7i Thomas Hunt Morgan\u2019\u0131n Kolombiya \u00dcniversitesi\u2019ndeki me\u015fhur Drosophila laboratuvar\u0131nda (\u201cSinek odas\u0131 – Fly room\u201d), Mendel geneti\u011finin ilkeleri \u00fczerinden, \u00e7e\u015fitli morfolojik mutantlar\u0131n kullan\u0131m\u0131yla, biyolojik de\u011fi\u015fkenli\u011fin genetik temelinin arz etti\u011fi evrensel sorunlar\u00a0 Drosophila melanogaster<\/em> kullan\u0131larak yo\u011fun bi\u00e7imde \u00e7al\u0131\u015f\u0131lmaktayd\u0131. Morgan, y\u00fczy\u0131l\u0131n hemen ba\u015flar\u0131nda, e\u015feye \u00f6zg\u00fc kal\u0131t\u0131m g\u00f6steren bir g\u00f6z mutant\u0131n\u0131 kullanarak, kal\u0131t\u0131m\u0131n kromozom teorisinin temelini atm\u0131\u015f, bir ba\u015fka deyi\u015fle, Mendel\u2019in kal\u0131t\u0131msal birim fakt\u00f6rlerini e\u015feye \u00f6zg\u00fc bir tonla yeniden renklendirmenin yolu iyice a\u00e7\u0131lm\u0131\u015ft\u0131.5<\/sup><\/p>\n

Fakat Morgan laboratuvar\u0131n\u0131n konumuz a\u00e7\u0131s\u0131ndan \u00f6nemi, b\u00fcy\u00fck genetik\u00e7inin Nobel \u00f6d\u00fcl\u00fcyle ta\u00e7lanan muazzam \u00e7al\u0131\u015fmalar\u0131ndan ziyade, 1927 y\u0131l\u0131nda d\u00f6nemin Sovyetler Birli\u011fi\u2019nden 1 y\u0131ll\u0131\u011f\u0131na Morgan\u2019la \u00e7al\u0131\u015fmaya gelen enteresan bir ki\u015fili\u011fin evrimsel biyolojiye yapaca\u011f\u0131 ola\u011fan \u00fcst\u00fc katk\u0131lar\u0131 bi\u00e7imlendirmesinde yatmaktad\u0131r: sonraki birka\u00e7 y\u0131l i\u00e7inde y\u0131ld\u0131z\u0131 muazzam \u015fekilde parlayacak olan, y\u00fczy\u0131l\u0131n en b\u00fcy\u00fck evrimsel biyologlar\u0131ndan Theodosius Dobzhansky, sadece 1 y\u0131l i\u00e7in, Morgan\u2019la \u00e7al\u0131\u015fmak \u00fczere geldi\u011fi Amerika\u2019dan bir daha d\u00f6nmeyecek ve ya\u015fam\u0131n\u0131n sonuna kadar ge\u00e7en yakla\u015f\u0131k 50 y\u0131ll\u0131k aktif zaman zarf\u0131nda, Darwinci evrimsel biyolojinin gidi\u015fat\u0131n\u0131 derinden etkileyecektir. \u00d6n\u00fcm\u00fczdeki ay kald\u0131\u011f\u0131m\u0131z yerden devam edece\u011fiz.<\/p>\n

Dipnotlar<\/strong><\/p>\n

1) Peter J. Bowler, The Eclipse of Darwinism: Anti-Darwinian Evolution Theories in the Decades around 1900<\/em>, Johns Hopkins, 1983.<\/p>\n

2) Ronald Aylmer Fisher, The Genetical Theory of Natural Selection<\/em>, Oxford University Press, 1930.<\/p>\n

3) J. B. S. Haldane, The Causes of Evolution<\/em>, Longmans, 1932.<\/p>\n

4) Sewall Wright, Evolution in Mendelian Populations, Genetics 16, 97-159, 1931.<\/p>\n

5) T. H. Morgan, Sex limited inheritance in Drosophila<\/em>, Science 32, 120-122, 1910.<\/p>\n

 <\/p>\n","protected":false},"excerpt":{"rendered":"

Ronald A. Fisher, JBS Haldane ve Sewall Wright. Evrimsel geneti\u011fin bu \u00fc\u00e7 kurucu babas\u0131 da, temelinde se\u00e7ilimle evrimle\u015fmenin yer ald\u0131\u011f\u0131 Darwinci evrimsel biyolojinin toparlan\u0131\u015f\u0131, yeniden bi\u00e7imleni\u015fi ve \u201cModern Sentez\u201de giden yolu d\u00f6\u015feyen ta\u015flar\u0131n olu\u015fturulmas\u0131 bak\u0131m\u0131ndan b\u00fcy\u00fck \u00f6neme sahiptir. Ge\u00e7en yaz\u0131m\u0131zda, Charles Darwin\u2019in evrimsel biyoloji bilimini do\u011furup \u015fekillendiren devrimci etkisinin, K\u00f6ken\u2019de \u00f6nceki benzerleriyle k\u0131yaslanamayacak \u00f6l\u00e7\u00fcde ayr\u0131nt\u0131l\u0131 […]<\/p>\n","protected":false},"author":67,"featured_media":15665,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[184,1475,21,32,231],"tags":[461,200,292,1474],"class_list":["post-15664","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-147-sayi","category-bilim-ve-tarih","category-biyoloji","category-evrim","category-molekuler-biyoloji-ve-genetik","tag-darwin","tag-evrim","tag-genetik","tag-turlerin-kokeni"],"acf":[],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t