The Araucana chickens originated in an area of Chile ruled by the Araucana indians. The Araucana chicken is a combination of two distinct breeds. The Collonocas, and the Quetros. The "Collonocas" laid blue eggs and were rumpless. The "Quetros", had tufts a tail and laid brown eggs. Over time a combination of these two breeds created the Araucana, a breed that is rumpless, tufted, and lays blue eggs.
The tufts are unique to the Araucana chickens. The tufts are a group of feathers that grow from a flap of skin near the ear called a peduncle. The tufts gene is lethal when two copies are passed to the embryo, and the chick dies in the shell and does not hatch. So living tufted birds only carry 1 copy of the gene and that is why a tufted bird can have cleanfaced offspring. A cleanfaced bird is one that does not carry the tufting gene and cannot pass it on.
The is also a lot of variance in the shape and size of tufts. The shape of a parents tufts can have little bearing on the tufts a chick will have. A unilaterily tufted Aruacana (a tuft on only 1 cheek ) can have a chick that is bilaterily tufted ( a tuft on each cheek ). A bird with huge georgous tufts can have offspring that have tiny little barely there tufts.
Since it only takes 1 copy of the tufting gene to produce tufts and two copies are lethal. Many breeders pens are mixs of clean faced and tufted birds. If you mate a tufted roo to a clean faced hen you will get 50% tufted and 50% cleanfaced and have none die in shell from tufting. If you breed tufted to tufted you will get 50% tufted, 25% clean faced, and 25% dead in the shell. You end up with the same amount of tufted chicks either way.
Araucanas are rumpless which means they do not have a tail or tail bone. The trait that producess rumplessness is a non-lethal gene unlike the tufting gene. Though the gene is non-lethal it can cause difficulties. It can produce very short bodied birds that are not only unbecoming, they have a tendancy to have what is called poopy but. Because of this some breeders have a few tailed birds in their breeding pens. However mating a rumpless bird to a tailed bird results in 50% rumpless and 50% tailed. Some of the birds will only be partly tailed or rumpless due to various modifying genes.
Araucanas are supposed to lay a blue egg. The blue color is a liver bile pigment that is deposited throughout the egg at the same time as the calcium carbonate that makes up the egg shell. Therefor the blue color is on the inside of the shell as well as the outside. This is different from the brown shell color seen in other breeds. The brown color is deposited on the outside of the shell just before the egg is laid. If you crack open a brown egg it will be white on the inside.
Some Araucana lay a green or olive egg. This indicates the presence of a brown egg layer somewhere in the birds history. The inside of the egg will still be blue, while the outside is green or olive because the brown color is merely deposited on the outside. To overcome this you would breed the bird to an Araucana that hatched from a blue egg, then only breed to the chickens that lay the bluest eggs. Eventually you would have only blue egg laying chickens. It takes a while though.