What Causes a Standard-size Bird to Become a Bantam?

[Blackberry18]

Hey, I've wondered about this for a while, because I noticed about looking in my copy of The Standard of Perfect that many (not all) Bantam breeds accepted by the APA often have a Standard size, too, like Brahmas, Cochins, Plymouth Rocks, etc. I asked my friend about it, and her answer wasn't quite pertaining to Bantams, but she said that her in-breeding of Jersey Giants, the size was quite a bit smaller than the Standard size.

So, I want to know what makes a Standard-sized breed become a Bantam? Is it dominant or recessive gene? Like my friend said, in-breeding? I don't have The Bantam Standard by the ABA, unfortunately, so am also wondering if that includes Bantam breeds from the The Standard of Perfection, which I'm guessing it does, but what features make a Bantam eligible to be accepted by the ABA (and APA?). Thanks in advance!

Blackberry18

 

[rainbowrooster]

A bantam is 1/4 to 1/5 the size of large fowl. There are also breeds of bantams that don't exist as large fowl. Like any other physical trait that you see in animals there are genes specific to bantams. If batamism were the result of too much inbreeding then an infusion of new blood would restore them to a full sized fowl.

The ABA recognizes more varieties of bantam breeds than the APA does. The ABA is only about bantams so it does make sense to me that they would be more inclusive to a greater variety of bantams. The ABA has its own qualifying process (as does the APA) for accepting any new variety or breed of bantam