Sforno on Genesis 1:24/ספורנו על בראשית א׳:כ״ד

1תוצא הארץ נפש חיה, earth should produce living creatures possessing a quality of life superior to that of the plants.

2ויהי כן, it was exactly so, i.e. without omissions or additions. If any of the components of these creatures (genes) were to be missing, they would lose the ability to procreate in kind.