They are a specific breed of chicken. 100% chicken. As far as I know turkeys cant make hybrids the way chickens/guines or guineas/peafowl can but im not totally positive about that since Ive never heard anyone talk about turkey hybrids.
The correct name for a turken is Naked Neck I think, and they are originally from eastern Europe.
Turkens are a pure breed of chickens. They just have the nickname Turkens. They are also called Naked Necks. I have never heard of a turkey breeding with any other type of poultry. Guineas do it with other birds. Here is a thread about one. https://www.backyardchickens.com/forum/viewtopic.php?id=263053&p=1
Turkey-chicken hybrids: a cytological study of early development
K. Harada, and E. G. Buss
Kyushu University Fukuoka, Japan
Pennsylvania State University University Park, PA 16802.
Abstract
Reciprocal hybridization experiments were performed between the line of Beltsville Small White turkeys that has been selected for high incidence of parthenogenesis and two strains of chickens. The eggs were examined cytologically at early stages of development. In the cross of turkey females X chicken males, it was found that both male (2A-ZZ) and female (2A-ZW) zygotes are formed, but the latter are much less viable and usually die in a very early stage of development. Besides the hybrid embryos, parthenogenetic-type embryos also were found. In the cross of chicken females X turkey males, no evidence of successful hybridization was obtained. However, cell division was initiated in 100 percent of the chicken eggs. This fact suggests that turkey sperm had some enhancing effect on parthenogenetic cell division in chicken eggs.