Each time you donate DNA, you will receive Coins. The amount of Coins you receive depends how much you donate and the creature’s rarity. There is also a daily maximum of Coins you can receive from donations based on your current player level. 

To see how many Coins will be returned on your donation, tap on the “i” icon in the right corner of the request panel. The player you are donating to will not lose any Coins when you receive them.