Description:
The Sex-Linked Brown gene in coturnix quail causes the bird to be a slightly lighter shade of brown than wildtype--in between the clean pharaoh color and pale red color of Ginger and Roux (1). There are several claimed "tricks" to telling if a bird has SLB, including looking for muddy face color, a red-shaped "x" on the back, but it has not been documented if this is actually caused by SLB or just general variance in normal pharaoh.
Sex-linked brown is believed to be fairly common in backyard flocks, as it is hard to see and even harder to breed out. It is recessive, meaning you have to test breed individual birds for several generations to ensure they don't have the gene. Males with only one copy of the gene do not show any signs of SLB. Ginger, Roux, and SLB are all on the same locus (3), so a hen can either have Ginger, SLB, or Roux, but not more than one at a time. Roux and Ginger can be used to remove SLB from a breeding program.
Because SLB is sexlinked, meaning it transfers to male and female offspring differently. It was originally used in production flocks to sex chicks at hatch, but the differences between SLB and Pharaoh are faint in adults and even harder to see as chicks, and Roux or Ginger is generally used instead because it is easier to see (5).
Breeding SLB:
SLB Male x SLB Female = 100% SLB chicks
SLB Male x Clean Female = SLB females, het. SLB males
Clean Male x SLB Female = 100% clean female chicks, 100% het. SLB male chicks
Het. SLB male x SLB Female = 50% SLB female chicks, 50% clean female chicks, 50% het. SLB male chicks, 50% SLB male chicks
Het. SLB male x Clean Female = 50% clean female chicks, 50% SLB female chicks, 50% het. SLB male chicks, 50% clean male chicks.
Note: it is impossible to have a heterozygous female chick, as females can only have one Z chromosome, and the "pair" or the W chromosome is short, meaning it forces the recessive mutation to show even with only one copy. This is called Hemizygous. Refer to the genetics series if you would like to read more.
References & Further Reading
F Minvielle, S Ito, M Inoue-Murayama, M Mizutani, N Wakasugi, Brief communication. Genetic analyses of plumage color mutations on the Z chromosome of Japanese quail, Journal of Heredity, Volume 91, Issue 6, November 2000, Pages 499–501, https://doi.org/10.1093/jhered/91.6.499
Mishra, S. K., Khan, A. A., Narayan, R., Singh, S. P., Pratap, S. O., Saxena, D., & Chaudhuri, D. (2011). Inheritance of plumage colour variations in a large flock of Japanese quail. British Poultry Science, 52(6), 686–693. https://doi.org/10.1080/00071668.2011.640306
Cheng, K.M., Kimura, M.: Mutations and major variants in Japanese quail. In: Crawford, R.D. (ed.) Poultry Breeding and Genetics, pp. 333–362 (1990)
Somes, Ralph G. Jr., "International Registry of Poultry Genetic Stocks" (1988). Storrs Agricultural Experiment Station. 29. https://digitalcommons.lib.uconn.edu/saes/29
Komarchev, A. (2021, June). Autosexing Japanese Quails (Coturnix Japonica). In International Scientific Conference Fundamental and Applied Scientific Research in the Development of Agriculture in the Far East (pp. 864-871). Cham: Springer International Publishing.
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