Crested Khaki throw back?

[Kadjain]

How did these crested Khaki's come from non crested parents?
One has a small crest and the other a righteous afro!
I had a previous Khaki hatch with a small one but it went away after a couple weeks. These are 6 weeks old now and their crests are still going strong.

 

[ducklover87]

Maybe one of the grandparents of these ducks were crested? That would be how only a few have it. Also the crest is a deformity in the skull so maybe one of the parents is carrying that gene. Either way it sounds like its a recessive gene from one of the parents whether due to bloodlines or the parent itself.