Description:
The clench gene in quail is a little-studied mutation that causes quail to be born with curled toes that didn't self-correct, and is strong enough to prevent the chicks from walking properly on their feet. It has an overall look of a clenched human fist, hence the name. The toes were curled up to the top joint on the foot, and both chicks and adults (1).
The bird tends to walk on either the side of their curled feet, or the actual joint itself (1), also coining the term "clubfoot", though this gene is different from both the clubfoot gene in humans and curled toe gene found in chickens. In chickens, the curled toe gene is less prominent (1), with the toes curling sideways forming a fleur de lises look, where with the clenched foot gene the toes curl completely inwards. It is uncertain if the clenched foot is found in other fowl, or if quail have the same recessive curled toe gene as well as the clenched foot gene (2).
Part of the reason this gene isn't as studied or well-known is likely because the condition can also be environmental. A similar clenched foot trait can also be found in chickens that fail to develop their leg muscles properly during hatching, either from a riboflavin (3) or linoliec acid deficiency (4), or from pulling the chick from the shell (5). Though these studies are done on chickens, many of them can also be applied to quail.
Because the gene is also recessive, it is unknown how common it is in backyard breeder flocks. There have been no studies to determine whether the majority of club foot in backyard flocks is genetic or environmental. It is recommended to ensure the incubator temperature and humidity is accurate as well as the feed of the hens.
Clench x Clench = 100% Clench
Clench x Normal = 100% Carrier
Clench x Carrier = 50% Clench, 50% Carrier
Carrier x Carrier = 25% Clench, 50% Carrier, 25% Normal
Carrier x Normal = 50% Carrier, 50% Normal *
*Because you cannot see if a bird is a carrier for clench, it is possible for the gene to hide in lines for generations. The best way to prevent this is to keep track of any chicks with club/clench foot and cull them (remove from your breeding program).
References & Further Reading
Nakane Y, Tsudzuki M. Clench: a new autosomal recessive mutation in Japanese quail. The Journal of Heredity. 1998 Jul-Aug;89(4):347-348. DOI: 10.1093/jhered/89.4.347. PMID: 9703690.
Tsudzuki, M. (2008). Mutations of Japanese quail (Coturnix japonica) and recent advances of molecular genetics for this species. The journal of poultry science, 45(3), 159-179.
Bethke, R. M., & Record, P. R. (1942). The relation of riboflavin to growth and curled-toe paralysis in chicks. Poultry Science, 21(2), 147-154.
Menge, H. (1970). A Toe Deformity in the Progeny of Linoleic Acid Deficient Hens. Poultry science, 49(2), 553-556.
Bakhuis, W. L. (1974). Observations of hatching movements in the chick, Gallus domesticus. Journal of comparative and physiological psychology, 87(5), 997.