{"id":8119,"date":"2013-10-11T20:10:28","date_gmt":"2013-10-11T18:10:28","guid":{"rendered":"http:\/\/www.ilkkimbuldu.com\/?p=8119"},"modified":"2018-10-03T16:12:16","modified_gmt":"2018-10-03T14:12:16","slug":"genetik-bilimi-kurucusu-kim","status":"publish","type":"post","link":"https:\/\/www.ilkkimbuldu.com\/?p=8119","title":{"rendered":"Genetik Bilimi kurucusu kim"},"content":{"rendered":"

Geneti\u011fin \u00f6zerk bilim olarak yerle\u015fmesi i\u00e7in a\u015fa\u011f\u0131 yukar\u0131 iki y\u00fczy\u0131l gerekmi\u015ftir ve Maupertius<\/strong> (1698-1759), ilk ger\u00e7ek genetik\u00e7i say\u0131labilir. Voltaire\u2019in Dr. Akakia ad\u0131yla g\u00fcl\u00fcn\u00e7le\u015ftirmeye \u00e7al\u0131\u015ft\u0131\u011f\u0131 bu dahi bilim adam\u0131, bu konuda her \u015feyi sezmi\u015f, \u00f6nceden g\u00f6rm\u00fc\u015f ve bulmu\u015ftur: Mendel yasalar\u0131; kal\u0131t\u0131mla ilgili kromozom kuram\u0131; de\u011fi\u015finimler.<\/p>\n

Genetik tarihi, \u00fc\u00e7 ayr\u0131 ara\u015ft\u0131rma d\u00fczeyiyle ilgili \u00fc\u00e7 d\u00f6neme ayr\u0131labilir. 1900\u2019e kadar iki isim g\u00f6ze \u00e7arpar: Naudin<\/strong> ve Gregor\u00a0Mendel<\/strong><\/a>. O tarihte kal\u0131t\u0131m bilimi emeklemekte, yaln\u0131zca ana-babalar ile \u00e7ocuklar aras\u0131ndaki benzerli\u011fi sa\u011flayan do\u011fal yasalar\u0131 ortaya \u00e7\u0131karma\u011fa \u00e7al\u0131\u015fmaktad\u0131r. 1900\u2032 de, h\u00fccre geneti\u011finin destans\u0131 d\u00f6nemi ba\u015flar: \u00d6zg\u00fcl \u00f6zelliklerin \u00e7ekirdek i\u00e7inde bulunan ve \u00abkromozom\u00bb denen harika birimlerde bulundu\u011fu ortaya \u00e7\u0131kar\u0131l\u0131r. 1953\u2019te Francis Crick<\/strong> ve James Watson<\/strong> taraf\u0131ndan deoksiribon\u00fckleik asidin ve genetik \u015fifrenin gizinin \u00e7\u00f6z\u00fclmesiyle, molek\u00fcl geneti\u011fi \u00e7a\u011f\u0131na girilir.<\/p>\n

Soya\u00e7ekimin bin bir gizini ayd\u0131nlatma giri\u015fiminde, bu i\u015fe en uygun deney gere\u00e7lerini kullanmak gerekir. Daha 1863 y\u0131llar\u0131nda Naudin, melezlerden yola \u00e7\u0131karak, yak\u0131n iki tatula (patatesle akraba, sanr\u0131 uyand\u0131r\u0131c\u0131 bitki) t\u00fcr\u00fcn\u00fc \u00e7aprazlam\u0131\u015ft\u0131. Ama Avusturyal\u0131 ke\u015fi\u015f Johann Gregor Mendel<\/strong>, ayr\u0131 altt\u00fcrden (\u00e7e\u015fit, \u0131rk) tohumluklar kullanma becerisini g\u00f6sterdi. Bu din adam\u0131, g\u00fcn\u00fcm\u00fczde \u00c7ekoslovakya\u2019 da bulunan Bmo manast\u0131r\u0131n\u0131n bah\u00e7esinin bir k\u00f6\u015fesinde, kendid\u00f6llek, \u00e7ok d\u00f6l verimli ve h\u0131zl\u0131 b\u00fcy\u00fcyen bir sebze olan bezelyeler \u00fcst\u00fcnde \u00e7al\u0131\u015ft\u0131. G\u00f6zlemlerinin sonu\u00e7lar\u0131n\u0131, Versuche \u00dcber Pflanzenhybriden (\u00c7e\u015fitli Bitki Melezleri \u00dcst\u00fcne Ara\u015ft\u0131rmalar) -[1865] ad\u0131yla yay\u0131nlad\u0131. O zamanki bilim d\u00fcnyas\u0131n\u0131n k\u00fc\u00e7\u00fcmsedi\u011fi bu yap\u0131t, ancak aradan 35 y\u0131l ge\u00e7tikten sonra, Correns, Hugo de Vries ve \u00c7ermak\u2019\u0131n yeni bulu\u015flar\u0131yla hakketti\u011fi \u00f6neme kavu\u015ftu.<\/p>\n

Mendel yasalar\u0131 \u00fc\u00e7 tanedir ve \u015f\u00f6yle \u00f6zetlenebilir:<\/h2>\n

1) Birinci ku\u015fakta, b\u00fct\u00fcn melezler birbirine benzer;<\/p>\n

2) \u0130kinci ku\u015fakta, melezler ayr\u0131\u015f\u0131kt\u0131r, kal\u0131t\u0131msal \u00f6zellikler birbirine benzemez;<\/p>\n

3) Bir \u00e7iftte ya da belli bir \u00f6zellik grubunda, \u00f6zelliklerin her biri ba\u011f\u0131ms\u0131z olarak kendini g\u00f6sterir. Bu savlar\u0131 do\u011frulamak i\u00e7in, baz\u0131 deneylere giri\u015fmek yeterlidir.<\/p>\n

Bir yerde, biri k\u0131rm\u0131z\u0131, \u00f6teki beyaz \u00e7i\u00e7ekli olan iki gecesefas\u0131 \u00e7e\u015fidi yeti\u015ftirilir ve birinin di\u015fici\u011fi \u00f6tekinin \u00e7i\u00e7ek- tozlar\u0131yla d\u00f6llenirse, birinci ku\u015fakta b\u00fct\u00fcn melezlerin pembe \u00e7i\u00e7ekli oldu\u011fu g\u00f6r\u00fcl\u00fcr Bu iki \u00abyeni\u00bb \u00e7i\u00e7ek kendi aralar\u0131nda d\u00f6llendirilip \u00e7o\u011falt\u0131l\u0131rsa, elde edilen \u00e7i\u00e7eklerin y\u00fczde 25\u2019inin k\u0131rm\u0131z\u0131, y\u00fczde 25\u2019inin beyaz, y\u00fczde 50\u2019sinin pembe oldu\u011fu g\u00f6r\u00fcl\u00fcr. Bundan sonra art\u0131k k\u0131rm\u0131z\u0131lar yaln\u0131z k\u0131rm\u0131z\u0131, beyazlar yaln\u0131z beyaz \u00e7i\u00e7ek verecek, ama pembeler gene belli oranlarda (1\/4, 1\/4, 1\/2} k\u0131rm\u0131z\u0131, beyaz ve pembe \u00e7i\u00e7ekler vereceklerdir.<\/p>\n

Bu uyumlu sonu\u00e7lar\u0131n yorumlanmas\u0131, pek de karma\u015f\u0131k de\u011fildir. T\u00fcm\u00fc iki s\u00f6zc\u00fckle \u00f6zetlenebilir: Fenotip; genotip. Bir organizman\u0131n d\u0131\u015f g\u00f6r\u00fcn\u00fc\u015f\u00fc, s\u00f6zgelimi rengi, onun fenotipidir. Yar\u0131s\u0131 babadan, yar\u0131s\u0131 anadan gelen kal\u0131t\u0131msal varl\u0131\u011f\u0131 ise, \u00abgenotip\u00bb denen \u015feyi olu\u015fturur. Demek ki, fenotip ile genotipin mutlaka uyu\u015fmas\u0131 gerekmez.<\/p>\n

BB genotipli beyaz (B) gecesefas\u0131yla \u00e7aprazlanan KK genotipli k\u0131rm\u0131z\u0131 (K) gecesefas\u0131, ilk ku\u015fakta pembe feno- tipli ve KB genotip\u0131li melezler verir. \u0130kinci ku\u015fakta, 1\/4 oran\u0131nda ar\u0131 k\u0131rm\u0131z\u0131 \u0131rk KK, 1\/4 oran\u0131nda an beyaz \u0131rk BB ve 1\/2 oran\u0131nda yeni pembe melezler KB ortaya \u00e7\u0131kt\u0131\u011f\u0131 g\u00f6r\u00fcl\u00fcr. Ba\u015fka bir deyimle, \u00abe\u015fit\u00bb g\u00fc\u00e7te beliren K ve B \u00f6zellikleri, bir ara renkte birle\u015fip erir.<\/p>\n

T\u0131pk\u0131 Mendel gibi, bezelyelerle \u00e7al\u0131\u015f\u0131lmak istenirse, bir b\u00f6l\u00fcm\u00fc p\u00fcr\u00fczs\u00fcz, bir b\u00f6l\u00fcm\u00fc k\u0131r\u0131\u015f\u0131k olan bezelyeler ele al\u0131n\u0131r. O zaman birinci ku\u015fakta, b\u00fct\u00fcn melezlerin p\u00fcr\u00fczs\u00fcz taneli oldu\u011fu g\u00f6r\u00fcl\u00fcr. Bu p\u00fcr\u00fczs\u00fcz (P) \u00f6zellik, bask\u0131n \u00e7\u0131kt\u0131\u011f\u0131 ve kendi fenotip yasas\u0131n\u0131 kabul ettirdi\u011fi i\u00e7in ba\u015fat say\u0131l\u0131r; buna kar\u015f\u0131l\u0131k, daha s\u00f6n\u00fck ve \u00e7ekingen olan k\u0131r\u0131\u015f\u0131k (k) \u00f6zellik, \u00abba\u015fat\u00bb ad\u0131na kar\u015f\u0131 \u00ab\u00e7ekinik\u00bb ad\u0131n\u0131 al\u0131r. \u0130kinci ku\u015fak ya da d\u00f6lde, tanelerin 1\/4\u2019\u00fc ar\u0131 k\u0131r\u0131\u015f\u0131k (rr) \u0131rk, 1\/4\u2019\u00fc an p\u00fcr\u00fczs\u00fcz (PP) \u0131rk ve 1\/2\u2019si melez p\u00fcr\u00fczs\u00fcz (Pk) \u0131rk olur.<\/p>\n

B\u00fct\u00fcn bu varsay\u0131msal hesaplar bo\u015f g\u00f6r\u00fcnebilir, ama bu konuda \u00e7ok verimli deneyler de yap\u0131lm\u0131\u015ft\u0131r. S\u00f6zgelimi, \u00abye\u015fil devrim\u00bbin yarat\u0131c\u0131s\u0131 Dr. Borlaug<\/strong>\u2019un, b\u00fct\u00fcn bulu\u015flar\u0131n\u0131 Mendel\u2019e bor\u00e7lu oldu\u011fu s\u00f6ylenebilir. Verimli ama kurakl\u0131\u011fa dayan\u0131ks\u0131z bir bu\u011fday ile verimi az ama kurakl\u0131\u011fa dayan\u0131kl\u0131 bir bu\u011fday\u0131 \u00e7aprazla\u015ft\u0131rarak, hem verimli, hem de dayan\u0131kl\u0131 bir bu\u011fday cinsi yaratm\u0131\u015ft\u0131r.<\/p>\n

Ayn\u0131 bi\u00e7imde, Johann Gregor Mendel<\/strong>\u2019in \u00e7al\u0131\u015fmalar\u0131, yeni g\u00fcl, karnabahar ve k\u00f6pek \u0131rklar\u0131n\u0131n yarat\u0131lmas\u0131na, harika bir m\u0131s\u0131r\u0131n k\u00f6yl\u00fcn\u00fcn hizmetine sunulmas\u0131na, hayvanc\u0131lara az yiyen, \u00e7ok s\u00fct veren hayvanlar, tavuk\u00e7ulara ola\u011fan\u00fcst\u00fc yumurtlay\u0131c\u0131 tavuklar sa\u011flanmas\u0131na, \u00fcst\u00fcn verimli yoncalar, d\u00fc\u015f \u00fcr\u00fcn\u00fc gibi orkideler \u00fcretilmesine, hatt\u00e2 XVII. y\u00fczy\u0131lda ortadan kalkan Avrupa yaban s\u0131\u011f\u0131r\u0131n\u0131n b\u00fct\u00fcn \u00f6zellikleriyle yeniden yarat\u0131lmas\u0131na (Korsika bo\u011fas\u0131 ve \u0130sko\u00e7 ine\u011fi kullan\u0131larak) olanak vermi\u015ftir.<\/p>\n

Mendel yasalar\u0131, t\u0131pta da eski g\u00f6r\u00fc\u015fleri darmada\u011f\u0131n etti. Soydan ge\u00e7en pek \u00e7ok kusurun aktar\u0131lmas\u0131n\u0131 \u00f6rten perde, onlar sayesinde kald\u0131.Hemofili (kanama hastal\u0131\u011f\u0131) ve fenilketon i\u015feme gibi, \u015feker hastal\u0131\u011f\u0131 ve vereme yatk\u0131nl\u0131\u011f\u0131n da \u00e7ekinik \u00f6zellik bi\u00e7iminde aktar\u0131ld\u0131\u011f\u0131 bilinmektedir; buna kar\u015f\u0131l\u0131k, soydan ge\u00e7me alyuvary\u0131k\u0131m\u0131 hastal\u0131\u011f\u0131 ba\u015fat olarak aktar\u0131l\u0131r. Ba\u015fka \u00f6zellikler de, \u00f6zellikle Albin hastal\u0131\u011f\u0131 (albinizm), bunlara benzer \u00e7izimlerle a\u00e7\u0131klanabilir.<\/p>\n

G\u00f6z rengine gelince, kahverengi g\u00f6zl\u00fc ana ve babadan mavi bir \u00e7ocuk do\u011fabilir, ama kahverengi maviye g\u00f6re ba\u015fatt\u0131r; buna kar\u015f\u0131l\u0131k, ikisi de mavi g\u00f6zl\u00fc ana ve babadan, kahverengi g\u00f6zl\u00fc bir \u00e7ocuk do\u011fmaz. \u00d6rnekler pek \u00e7oktur (kan gruplar\u0131, Rh\u00e9sus etkeni, burun bi\u00e7imi, vb.).<\/p>\n

B\u00fct\u00fcn bunlardan toplu bir sonu\u00e7 \u00e7\u0131kar\u0131lmak istenirse, \u015f\u00f6yle denebilir: Saf \u0131rklar\u0131n ve yak\u0131n kan akrabalar\u0131n\u0131n birle\u015fmesi (evlenmesi), anormal \u00f6zelliklerin kar\u015f\u0131la\u015fma tehlikesini art\u0131r\u0131r; buna kar\u015f\u0131l\u0131k melezlik, yozla\u015fm\u0131\u015f genleri t\u00f6rp\u00fcler, kalabal\u0131k i\u00e7inde yitirir. Hitler, \u00e7\u0131lg\u0131n d\u00fc\u015f\u00fcn\u00fc ger\u00e7ekle\u015ftirebilseydi, s\u00f6zde \u00fcst\u00fcn Ari \u0131rk\u0131, olsa olsa soysuzla\u015fm\u0131\u015f bir k\u00fctleye d\u00f6n\u00fc\u015ft\u00fcrmeyi ba\u015farabilirdi. Irk gruplar\u0131n\u0131n i\u00e7ine kapal\u0131 ya\u015famas\u0131, n\u00fcfusun sa\u011fl\u0131\u011f\u0131n\u0131 bozar, kar\u0131\u015fmalar\u0131ysa g\u00fc\u00e7lendirir. Y\u00f6ntemleri ne olursa olsun, \u0131rk\u00e7\u0131l\u0131k, ula\u015fmak istedi\u011fi ama\u00e7lara bile ayk\u0131r\u0131 d\u00fc\u015fer: Laboratuvarlardaki beyaz s\u0131\u00e7anlar,yabani tarla s\u0131\u00e7anlar\u0131na g\u00f6re, kurnazl\u0131k bilmeyen, hi\u00e7 bir vir\u00fcs hastal\u0131\u011f\u0131na kar\u015f\u0131 koyamayan, g\u00fc\u00e7s\u00fcz ve zavall\u0131 hayvanlard\u0131r.<\/p>\n

Mendel a\u015famas\u0131ndaki genetik, kal\u0131t\u0131m\u0131n g\u00f6r\u00fcn\u00fcr olaylar\u0131n\u0131 a\u00e7\u0131klama a\u00e7\u0131s\u0131ndan yeterli hi\u00e7 bir eksi\u011fi bulunmayan, tam bir bilimdir. Ama gene de a\u00e7\u0131klanmas\u0131 gereken temel bir sorun kalmaktad\u0131r-. Geneti\u011fin inceledi\u011fi ya da ele ald\u0131\u011f\u0131 \u00f6zellikler, neyle ta\u015f\u0131nmaktad\u0131r?<\/p>\n

Kal\u0131t\u0131m\u0131n soya\u00e7ekimle ilgili kromozom kuram\u0131<\/h2>\n

Kal\u0131t\u0131m\u0131n soya\u00e7ekimle ilgili kromozom kuram\u0131, \u00f6zellikle A.B.D\u2019li Thomas Hunt Morgan\u2019\u0131n yap\u0131t\u0131d\u0131r\u2019. Morgan, bir s\u00fcr\u00fc sirkesine\u011fi, yani kara kar\u0131nl\u0131 sirkesine\u011fi (Drosophila melanogaster) yeti\u015ftirmi\u015ftir; \u00e7\u00fcnk\u00fc bu b\u00f6ceklerin, h\u00fccre \u00e7ekirdeklerinde 8 kromozom (4 \u00e7ift) ta\u015f\u0131mak gibi b\u00fcy\u00fck bir \u00fcst\u00fcnl\u00fckleri vard\u0131r.<\/p>\n

Kromozomlar, h\u00fccre b\u00f6l\u00fcnmesi an\u0131nda belirginle\u015fen, e\u011fri b\u00fc\u011fr\u00fc k\u00fc\u00e7\u00fcc\u00fck ipliklerdir. Morgan, her t\u00fcrdeki kromozom say\u0131s\u0131n\u0131n de\u011fi\u015fmez oldu\u011funu \u00e7ok \u00e7abuk fark etmi\u015ftir. G\u00fcn\u00fcm\u00fczde solucanda 2, farede 40, ipekmaymunda ve insanda 46, goril ve \u015fempanzede 48, k\u00f6pekte 78 ve tatl\u0131su \u0131stakozunda 200 kromozom yabani tarla s\u0131\u00e7anlar\u0131na g\u00f6re, kurnazl\u0131k bilmeyen, hi\u00e7 bir vir\u00fcs hastal\u0131\u011f\u0131na kar\u015f\u0131 koyamayan, g\u00fc\u00e7s\u00fcz ve zavall\u0131 hayvanlard\u0131r.<\/p>\n

Mendel a\u015famas\u0131ndaki genetik, kal\u0131t\u0131m\u0131n g\u00f6r\u00fcn\u00fcr olaylar\u0131n\u0131 a\u00e7\u0131klama a\u00e7\u0131s\u0131ndan yeterli hi\u00e7 bir eksi\u011fi bulunmayan, tam bir bilimdir. Ama gene de a\u00e7\u0131klanmas\u0131 gereken temel bir sorun kalmaktad\u0131r-. Geneti\u011fin inceledi\u011fi ya da ele ald\u0131\u011f\u0131 \u00f6zellikler, neyle ta\u015f\u0131nmaktad\u0131r?<\/p>\n

Kal\u0131t\u0131m\u0131n soya\u00e7ekimle ilgili kromozom kuram\u0131, \u00f6zellikle A.B.D\u2019li Thomas Hunt Morgan\u2019\u0131n yap\u0131t\u0131d\u0131r\u2019. Morgan, bir s\u00fcr\u00fc sirkesine\u011fi, yani kara kar\u0131nl\u0131 sirkesine\u011fi (Drosophila melanogaster) yeti\u015ftirmi\u015ftir; \u00e7\u00fcnk\u00fc bu b\u00f6ceklerin, h\u00fccre \u00e7ekirdeklerinde 8 kromozom (4 \u00e7ift) ta\u015f\u0131mak gibi b\u00fcy\u00fck bir \u00fcst\u00fcnl\u00fckleri vard\u0131r.<\/p>\n

Kromozomlar, h\u00fccre b\u00f6l\u00fcnmesi an\u0131nda belirginle\u015fen, e\u011fri b\u00fc\u011fr\u00fc k\u00fc\u00e7\u00fcc\u00fck ipliklerdir. Morgan, her t\u00fcrdeki kromozom say\u0131s\u0131n\u0131n de\u011fi\u015fmez oldu\u011funu \u00e7ok \u00e7abuk fark etmi\u015ftir. G\u00fcn\u00fcm\u00fczde solucanda 2, farede 40, ipekmaymunda ve insanda 46, goril ve \u015fempanzede 48, k\u00f6pekte 78 ve tatl\u0131su \u0131stakozunda 200 kromozom bulundu\u011fu bilinmektedir.<\/p>\n

Diployit 2n denen bu say\u0131, yaln\u0131z cinsel olmayan h\u00fccrelerde (beden h\u00fccreleri) ger\u00e7ekle\u015fir; gametlerde, n say\u0131s\u0131 kadard\u0131r ve haployit ad\u0131 verilir; bu durum, yumurta ve spermatozoyitlerin olu\u015fumu s\u0131ras\u0131nda bunlarda olu\u015fan \u00abkromatik indirgenme\u00bbye dayan\u0131r. Buna dayan\u0131larak, kromozomlar\u0131n, d\u00f6llenmi\u015f yumurtaya hem baba \u00f6zelliklerinin yar\u0131 pay\u0131n\u0131, hem ana \u00f6zelliklerinin yan pay\u0131n\u0131 getirdi\u011fi s\u00f6ylenebilir. Mendel yasalar\u0131n\u0131n sonu\u00e7lan da bunu \u00f6ng\u00f6r\u00fcyor, geriye bir ad\u0131m atmak kal\u0131yordu. \u0130\u015fte bu ad\u0131m\u0131 atan Morgan, bu a\u00e7\u0131klamay\u0131 getirdi.<\/p>\n

Erkek ve di\u015fi sirke sine\u011finde (drosophila) 4 \u00e7ift kromozomun \u00fc\u00e7 \u00e7ifti \u00f6zde\u015ftir (2\u2019si U, l\u2019i noktal\u0131 bi\u00e7imde); bunlara \u00abotozom\u00bb denir. D\u00f6rd\u00fcnc\u00fc \u00e7ift, di\u015fide birbirine benzer iki \u00e7ubuktan, erkekte bir \u00e7ubuk ile \u00e7engel bir \u00e7ubuktan olu\u015fur: Bunlara da \u00abhetero- zom\u00bb denir: Birincide XX, \u0130kincide XY. Gametlerin birle\u015fmesi s\u0131ras\u0131nda di\u015fi X kromozomlar\u0131, ya erkekten gelen bir X kromozomuyla birle\u015fir (o zaman bir di\u015fi do\u011far), ya da bir Y ile birle\u015fir (o zaman da bir erkek sinek olur). \u0130statistik a\u00e7\u0131s\u0131ndan, \u00e7\u00f6z\u00fcmlerden her ikisi i\u00e7in de olas\u0131l\u0131k ayn\u0131d\u0131r ve toplulukta iki cinsin e\u015fit olmas\u0131nda \u015fa\u015f\u0131lacak bir \u015fey yoktur.
\nDaha sonra yap\u0131lan b\u00fct\u00fcn ara\u015ft\u0131rmalar bu yorumu do\u011frulam\u0131\u015ft\u0131r: \u0130kikanatl\u0131larda. k\u0131nkanatl\u0131larda, bal\u0131klar\u0131n \u00e7o\u011funda, kurba\u011falarda, memelilerde (bu arada Homo sa- piens\u2019te yani insanda) di\u015filerde bir \u00e7ift benzer XX kromozomu, erkeklerde bir \u00e7ift bak\u0131\u015f\u0131ms\u0131z (birbirine denk olmayan) XY kromozomu bulunur. Kelebeklerde, ku\u015flarda, ve s\u00fcr\u00fcngenlerde bunun tersidir; yani erkeklerde XX, di\u015filerde XY kromozom \u00e7ifti vard\u0131r. Y\u2019ye ba\u015fat bir \u00f6zellik (XY bir melez oldu\u011funa g\u00f6re), X\u2019e de \u00e7ekinik bir \u00f6zellik (XX ar\u0131 bir \u0131rka kar\u015f\u0131l\u0131kt\u0131r) g\u00f6z\u00fcyle bak\u0131labilir.<\/p>\n

Kal\u0131t\u0131ma ili\u015fkin kromozom kuram\u0131m sa\u011flamla\u015ft\u0131rd\u0131ktan sonra, Morgan\u2019a bunun s\u00fcrecini belirlemek kal\u0131yordu. \u00d6zellikle sirkesine\u011finde saptanan 400 kadar etkenin (g\u00f6zlerin rengi, kanatlar, kanatlar\u0131n uzunlu\u011fu, vb.), Mendel\u2019in 3. yasas\u0131 (\u00f6zelliklerin ayr\u0131l\u0131\u011f\u0131) ge\u00e7ersizli\u011fini yitirmeden, nas\u0131l olup da bir ve b\u00fct\u00fcn olarak 4 \u00e7ift kromozom taraf\u0131ndan ta\u015f\u0131nabildi\u011fini a\u00e7\u0131klamas\u0131 gerekiyordu.<\/p>\n

Bu da birtak\u0131m deneylerle \u00e7\u00f6z\u00fcld\u00fc: Uzunkanatl\u0131 gri bir sirkesine\u011fi (UU GG) ile \u00e7otuk kanatl\u0131 kara bir sirkesine\u011fi (\u00e7\u00e7 kk) ikinci d\u00f6lde (ku\u015fakta), 9\u2019u genotip, 7\u2019si fenotip olan 16 birey olu\u015fturmaz; sineklerin y\u00fczde 75\u2019i uzun kanatl\u0131 gri, y\u00fczde 25\u2019i \u00e7otuk kanatl\u0131 kara olur. Her \u015fey, sanki bir yanda bulunan \u00abuzun\u00bb ve \u00abgri\u00bb etkenler,, \u00f6te yanda bulunan \u00ab\u00e7otuk\u00bb ve \u00abkara\u00bb etkenlerle ayr\u0131lmaz bir b\u00fct\u00fcnm\u00fc\u015f gibi olup biter. Burada bir linkaj (aralar\u0131nda mant\u0131kl\u0131 hi\u00e7 bir ba\u011f bulunmayan bir\u00e7ok kal\u0131t\u0131msal etmenin a\u015fa\u011f\u0131 yukar\u0131 de\u011fi\u015fmez bi\u00e7imde bir arada bulunmas\u0131) s\u00f6z konusudur: Sirkesine\u011finde her \u00e7ubuk kromozom yakla\u015f\u0131k olarak 60 \u00f6zellik, her U kromozom y\u00fczden \u00e7ok \u00f6zellik, her noktams\u0131 kromozom 5-10 \u00f6zellik ta\u015f\u0131r. \u0130nsanda, cinsel X ve Y kromozomlar\u0131nda kurulan linkajlar daha iyi anla\u015f\u0131lmaya ba\u015flanm\u0131\u015ft\u0131r.<\/p>\n

Olay g\u00f6r\u00fcnd\u00fc\u011f\u00fc kadar yal\u0131n de\u011fildir, linkaj\u0131n da kurald\u0131\u015f\u0131 durumlar\u0131 vard\u0131r: Yumurta spermatozoyitle d\u00f6llendi\u011fi s\u0131rada, kromozom iplikleri yeniden ortaya \u00e7\u0131kt\u0131\u011f\u0131 zaman, kromozomlardan biri k\u0131r\u0131l\u0131p kopabilir ve kar\u015f\u0131l\u0131\u011f\u0131 olan yere d\u00fczensiz bi\u00e7imde kaynayabilir. Bu durumlarda anormallik, bazen de hastal\u0131k ya da bir ucube ortaya \u00e7\u0131kar.<\/p>\n

Ara\u015ft\u0131rman\u0131n bu noktas\u0131nda, h\u00fccre geneti\u011fi, yerini molek\u00fcl geneti\u011fine b\u0131rak\u0131r. Kromozom geneti\u011fi, kromozomlar\u0131n kimyasal bile\u015fimi sorunu \u00e7\u00f6z\u00fcld\u00fc\u011f\u00fc g\u00fcnden beri dev ad\u0131mlar\u0131yla ilerlemektedir. Bunu, ara\u015ft\u0131rmac\u0131 Francis Crick ve James Watson\u2019a bor\u00e7luyuz; s\u00f6z konusu bilginlerin Nature (Do\u011fa) dergisinde yay\u0131nlad\u0131klar\u0131 Dezoksiribon\u00fckleik Asit \u0130\u00e7in Bir Yap\u0131 (1953) adl\u0131 \u00fcnl\u00fc ara\u015ft\u0131rma sayesinde, Mendel ve Morgan yeniden yorumlanabilmektedir.<\/p>\n

Kal\u0131t\u0131msal \u00f6zellikler, kromozomlar\u0131 olu\u015fturmak i\u00e7in birbirine ba\u011flanan uzun dezok- siribon\u00fckleik asit (E\u2019.N.A.) molek\u00fclleri olan genlerle ta\u015f\u0131nmaktad\u0131r (bu genlerin, bir tek kromozomda birka\u00e7 y\u00fcz ile birka\u00e7 bin aras\u0131nda de\u011fi\u015fti\u011fi san\u0131lmaktad\u0131r). D.N.A., bir \u00e7ifte n\u00fckleotit sarmal\u0131 bi\u00e7iminde tasarlanabilir; sarmal bi\u00e7iminde \u00e7ifte ip merdiveni and\u0131ran bu yap\u0131da, merdivenin kenarlar\u0131 fosfat ve \u015fekerlerden (de- zoksiriboz), basamaklar\u0131ysa pirik ya da pirimiclik bazlardan (adenin, sitozin, guanin, timin) olu\u015fmu\u015ftur. H\u00fccre b\u00f6l\u00fcnd\u00fc\u011f\u00fc zaman, D.N.A\u2019n\u0131n \u00e7ifte dal\u0131 t\u0131pk\u0131 bir fermuar gibi a\u00e7\u0131l\u0131r; \u00abD.N.A. polimeraz\u00bb denen bir enzim, onun e\u015flenmesini (t\u0131pat\u0131p kopyas\u0131n\u0131 yapmas\u0131n\u0131) y\u00f6netir; \u00f6yle ki, iki yavru h\u00fccrenin de \u00e7ekirde\u011fi, ana h\u00fccredekine denk ve onunla \u00f6zde\u015f bir genler toplam\u0131 edinmi\u015f olur.<\/p>\n

T\u00fcr\u00fcn de\u011fi\u015fmezli\u011fi b\u00f6ylece sa\u011flanm\u0131\u015f olur. Bu \u00f6yle bir de\u011fi\u015fmezliktir ki, yaln\u0131zca bir e\u015flenme (kopya) yanl\u0131\u015f\u0131yla ya da D.N.A. molek\u00fcl\u00fcndeki bir kopuklukla bozulabilir; o zaman da, bir de\u011f\u015finim (mutasyon) var demektir.<\/p>\n","protected":false},"excerpt":{"rendered":"

Geneti\u011fin \u00f6zerk bilim olarak yerle\u015fmesi i\u00e7in a\u015fa\u011f\u0131 yukar\u0131 iki y\u00fczy\u0131l gerekmi\u015ftir ve Maupertius (1698-1759), ilk ger\u00e7ek genetik\u00e7i say\u0131labilir. Voltaire\u2019in Dr. Akakia ad\u0131yla g\u00fcl\u00fcn\u00e7le\u015ftirmeye \u00e7al\u0131\u015ft\u0131\u011f\u0131 bu dahi bilim adam\u0131, bu konuda…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[92],"tags":[1232,2771],"class_list":["post-8119","post","type-post","status-publish","format-standard","hentry","category-bilim","tag-genetik","tag-gregor-mendel"],"_links":{"self":[{"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=\/wp\/v2\/posts\/8119"}],"collection":[{"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=8119"}],"version-history":[{"count":3,"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=\/wp\/v2\/posts\/8119\/revisions"}],"predecessor-version":[{"id":12256,"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=\/wp\/v2\/posts\/8119\/revisions\/12256"}],"wp:attachment":[{"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=8119"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=8119"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.ilkkimbuldu.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=8119"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}