Description:
There are a few different mutations that can cause crooked neck or other neck issues in quail. All of them are considered to be autosomal recessive, meaning that it can hide in a flock. They are grouped here because all of them present very similarly, cause the same issues in quail, and are inherited in the same manner. It is worth noting that most of these mutations and general neck issues in quail can also be caused from much more common nutritional issues.
The back-drawer mutation causes the quail's head to bow low and the bird to crouch about half of the time. It is called "back drawer" because of the bird's tendancity to draw backwards. Sometimes the bird rolls forward. Birds show symptoms before 8 weeks of age, and about 1/4 will die shortly after symptoms start. Symptoms come and go - there will be times the bird appears "normal", but will usually revert back to the back-drawer behavior. About half of the birds with back-drawer will recover completely without special care, but will have extremely low fertility for their lives. All birds, even after "recovery" died around or before 4 months of age. (All information in this paragraph from source 3).
Star-gazing, also called wry neck, causes the bird to tip their head upwards and rest it on their back for short periods of time. This throws them off-balance and causes them to spin in circles or move backwards, and sometimes walk on their hocks. It isn't lethal, and birds can live and reproduce with the condition if proper care is given, though the condition gets more pronounced with age. Chicks with stargazing usually present symptoms before 3 weeks that progressively get more common. (All information is from source 2).
Congenital loco (also called wry neck) is found in chickens, quail, and turkeys. Very similar to star-gazing, it causes the bird to throw its head back when excited, though it is typically seen within the first day of hatch, and get even more noticeable after a week of age. It presents as lethal, with about 80% of chicks dying within the first week and the rest dying before reaching a month old, likely from being unable to properly eat and drink. The fertility of these chicks were not tested. It has been suggested that star gazing is just a mild form of congenital loco, though this is unknown and not formally tested. (All information is from source 4). This has been confirmed to be on Chromosome 12. (5)
Crooked neck is a completely lethal mutation in quail that causes any bird with two copies of the gene to die in the shell. Embryo dissection reveals that the quail develops a sharply kinked neck, uneven beak lengths, and considerably smaller bodies. It is likely a dwarfing gene on top of causing neck issues. No bird is able to hatch because the neck prevents them from pipping properly. (All information in this paragraph is from source 1).
It is unknown how prevalent any of these genes are, and they are nor confirmed to be in public hands at this time. This is due to the recessive nature of all of them, and similar traits can also be observed from nutritional issues and incorrect incubation settings.
Breeding with Neck Mutations:
Neck Mutant x Neck Mutant = 100% Neck Mutants, if any chicks can survive to adulthood and are fertile.
Neck Mutant x Normal Birds = 100% NM Carriers, again dependant on how many full Neck Mutants can survive to adulthood and reproduce
Neck Mutant x NM Carriers = 50% Neck Mutants, 50% NM Carriers
NM Carrier x NM Carrier = 25% Normal Birds, 50% NM Carriers, 25% Neck Mutants
NM Carrier x Normal Birds = 50% NM Carriers, 50% Normal Birds (indistinguishable from each other)
References & Further Reading
K. SITTMANN, R. M. CRAIG, Crooked Neck Dwarfs in Japanese Quail, Journal of Heredity, Volume 58, Issue 1, January 1967, Pages 44–46, https://doi.org/10.1093/oxfordjournals.jhered.a107540
Savage TF, Collins WM. Inheritance of star-gazing in Japanese quail. J Hered. 1972 Mar-Apr;63(2):87-90. doi: 10.1093/oxfordjournals.jhered.a108236. PMID: 5031318.
TSUDZUKI, Masaoki, and Noboru WAKASUGI. "Back-drawer: a behavioral mutant in Japanese quail." Experimental Animals 37.2 (1988): 137-144.
Sittmann, K., Richards, W. P. C., & Abplanalp, H. (1965). CONGENITAL LOCO IN A THIRD SPECIES OF DOMESTIC FOWL. Canadian Journal of Genetics and Cytology, 7(4), 636–640. doi:10.1139/g65-084
Okumura Y, Ohtake T, Uemoto Y, Sato S, Sato S, Kobayashi E. Fine mapping of the chicken congenital loco locus on chromosome 12. Anim Genet. 2013 Dec;44(6):778-81. doi: 10.1111/age.12065. Epub 2013 Jun 7. PMID: 23742667.