Creatures do have maximum DNA caps per Creature Level based on their rarity. When the cap is reached, any additional DNA acquired in-game will not be added. The only exception for this is for any DNA acquired through purchased incubators. 

• Common: 850,000 DNA 
• Rare: 250,000 DNA
• Epic: 85,000 DNA 
• Legendary: 25,000 DNA 
• Unique: 8,000 DNA
• Apex: 3,000 DNA
• Omega: 60,000 DNA