The present invention provides a genetically modified non-human organism having higher Cas9 expression and capable of simultaneously editing a plurality of different genes or a plurality of locations within the same gene with high efficiency. In the genetically modified non-human organism of the present invention, the gene encoding Cas9 (CRISPR-associated 9) has at least 3 copies in the nuclear genome. The egg cell of the present invention is derived from a genetically modified non-human organism having a nuclear genome into which at least 3 copies of a gene encoding Cas9 have been introduced. The fertilized egg of the present invention is obtained by fertilizing the egg cell and sperm derived from the same species. The method for modifying a target gene of the present invention comprises a step of introducing a guide RNA into a cell derived from the genetically modified non-human organism, the egg cell, or the fertilized egg.本発明は、よりＣａｓ９の発現が高く、複数の異なる遺伝子又は同一遺伝子内の複数箇所を同時に高効率で編集可能な遺伝子改変非ヒト生物を提供する。本発明の遺伝子改変非ヒト生物は、Ｃａｓ９（ＣＲＩＳＰＲ－ａｓｓｏｃｉａｔｅｄ ９）をコードする遺伝子が核ゲノム中に少なくとも３コピーを有する。本発明の卵細胞は、Ｃａｓ９をコードする遺伝子が少なくとも３コピー導入された核ゲノムを有する遺伝子改変非ヒト生物由来である。本発明の受精卵は、前記卵細胞と、同種の生物由来の精子とを受精させてなる。本発明の標的遺伝子の改変方法は、前記遺伝子改変非ヒト生物由来の細胞、前記卵細胞、又は前記受精卵にガイドＲＮＡを導入する工程を備える。
