Селекция генов

В-третьих, один признак часто зависит от нескольких генов, поэтому при селекции генов со слабой наследуемостью аддитивность постепенно уменьшается. В-четвертых, некоторые благоприятные признаки сцеплены с неблагоприятными, вследствие чего нередко приходится довольствоваться компромиссом. И наконец, по истечении нескольких десятилетий сказываются последствия начального выбора. Селекция занимает длительный срок хотя бы потому, что цветение деревьев часто наступает довольно поздно: эвкалипт зацветает на третьем году жизни, на приморской сосне стробилы появляются только к шести годам, а на ели — только к двадцати. Правда, химическим путем можно ускорить сроки цветения, но эта операция осуществима лишь на небольшом количестве деревьев.

Выли попытки устранить некоторые недостатки и ускорить процесс селекции. Вместо отбора и прививки особей можно, например, создать участок одной семьи, состоящий из всего потомства особей F0 или его большей части. Внутри участка производится индивидуальная селекция но нескольким признакам с учетом свойств семьи и наследуемости каждого признака; при этом оптимизируют аддитивность двух или нескольких признаков, находящихся в неблагоприятной корреляции на уровне популяции. Такие работы были проведены с сосной приморской Pin us pinaster. В естественных популяциях встречаются незаурядные экземпляры, возникшие в результате случайных удачных генетических рекомбинаций. Иногда в практике контролируемого скрещивания получаются чрезвычайно удачные подборы пар, демонстрирующие удивительные и неожиданные свойства генетической рекомбинации. Селекция на уровне отдельных особей

Появление незаурядных экземпляров происходит гораздо чаше при гибридизации генетически далеких особей при скрещивании растений, имеющих разное географическое происхождение (но принадлежащих к одному виду), или при межвидовом скрещивании (когда оно возможно или когда его можно сделать таковым). Здесь речь идет о гетерозисе, явлении еще недостаточно понятом, связанном с гетерозиготностью.

 

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