The Swedish Black + the Silkie

Jamie Watter's Svart Hona Rooster

The Swedish Black chicken, shown, is for its dermal hyperpigmentation phenotype (it is all black).  While most have dark skin, like the Silkie and the Ayami Cemani, there are some that have lighter skin.

The paper by Anna M. Johannson in the Dept of Animal Breeding and Genetics, Swedish University of Agricultural Sciences, in  Uppsala, Sweden, discusses this in depth.

I've taken some of the highlights of Ms Johannsson's paper and put them here.

If you want the whole paper, contact me and I will gladly send the PDF with her contact details as well if you would like to follow up with further questions about her findings.

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There are 11 Swedish local chicken breeds of which two, the SvartHona and the Hedemorahona are discussed, because these as the breeds that are notably all-black.  Ms Johannsson's study was really about the their comb colour, that can be categorized into three categories: red, semi-dark and dark.

It was noted by the owners of these birds over several generation.  The males in particular

Jean Cavanagh's BIS Black Bearded Silkie Blessing

have all three comb colours while females tend to have only red or dark combs.  (I could find no examples of these combs, sorry).

The appearance of a red comb points to the involvement of the Z chromosome in the trait. Additional observations from a bird owner, who is interested in genetics, showed that the inheritance of comb colour can mostly be explained as a Z-linked inheritance, but that there are exceptions that do not fit with a single Z-linked locus (Johansson cites, Swedish breeder Thomas Englund, in  personal communications).

The Fm and id loci are known to be involved in the dark pigmentation phenotype in the Japanese Silkie (Bateson and Punnett, 1911; Dorshorst et al., 2010) as well (see an example of the Silkie from my friend Jean).

The now living birds in both of these breeds originate from small relics of earlier larger populations.

What we want to do is map the  loci associated with the comb colour trait segregated within the two breeds. To do this we genotyped 12 Bohuslän-Dals svarthöna and Hedemorahöna with the 60k SNP chip produced by Illumina for the GWMAS Consortium (Groenen et al., 2011). An association study was performed on the genotypes given the recorded comb colour phenotype.  The huslän-Dals svarthöna originates from the northern part of Bohuslän in western Sweden (close to the Norwegian border -- see map below for the location of Bohuslan, taken from Yahoo Maps.)

What was discovered was that around 1899, a woman got the ancestors of the current population of this breed as a wedding gift. Her two sons inherited the flock,  and in 1958 a man got the birds from the two brothers (Olsson, 2004).  These black birds are said to have be common in this area in old times and there is a legend stating that they are the descendants of birds that sailors brought back from long tours overseas to a foreign country.

 More than that is not explored in the paper but the diversity and inbreeding of the two breeds was,  with the mean inbreeding coefficient (F)  considerably larger in the samples from  Hedemorahöna than in the samples from Bohuslän-Dals svarthöna, and so it was concluded by genetic testing  that the Bohuslän-Dals svarthöna (black Swedish)  individuals were not inbred despite expectations.  That conclusion was derived as their  F coefficient was  less than or close to  zero, which under the Hardy-Weinberg equilibrium means that the these birds  are more heterozygous (different and less inbred) than higher numbers.

 However  half the Hedemorahöna individuals had a F coefficient that was great 0.1 and most of these had F>0.2  (see the supplementary Table 3 in the Johansson paper), with the most inbred  Hedemorahönas had F=0.45.