Tagyirpaziri baraksi irsiyat meboshad, vale bo on robitai zich dorad. Zero zarrachahoi irsi – genho in- kishofi in yo on alomatro muayyan mekunand. Agar aznavbarqaror- shavii qolab (matritsa) – molekulai KDN hamesha daqiq surat megirift, pas dar vaqti afzoishi organizmho faqat alomathoi peshtara az nasl ba nasl meguzashtand va mutobiqati namudho ba tagyiroti sharoiti muhiti zist nomumkin megasht. Az in ru, tagyirpaziri qobiliyati organizmho buda, baroi paydo kardani alomatu khosiyathoi nav khele muhim meboshad va dar natija tagy- iryobii sokhtori mavoddi irsi yo paydoishi genhoi navi omekhta ba amal meoyad.
Tagyirpaziri baroi intikhobi tabii mavoddi gunogun muhayyo mesozad, yane tagyirpaziri intikhobi fardhoe meboshad, ki ba sharoiti muhiti zist nagz mutobiq gashtaand. In ba paydo shuda- ni shakl va namudhoi navi organizmho musoidat mekunad.