An Ameraucana breeder on social media asked about the variance in color on her white Ameraucana chicks. Some were more yellow in color and others had more of a gray down. I thought I would start a thread on applicable scientific research on the subject.
From my understanding the down color variations in recessive white chicks have not been adequately clarified via research yet. If anyone else out there has come across something definitive please share it.
Some research reflects that the extended black (E) allele appears to be present when the recessive white chick downs have a gray cast (Jaap, 1943; Jeffrey, 1947). A cross of White Prat x Castellana by Campo in 1997 supported the hypothesis that the extended black allele (E) is necessary for gray or smokiness down to be present in recessive white chick down. However, in that particular study fewer than expected yellow chicks with gray down were observed. The expected proportion of white birds not carrying the columbian restriction gene (3/16) fit better, suggesting that E/- co+/co+ allows gray color to appear in recessive white chick down.
Jerome and Cavers (1952) completed a conflicting study that did not support the need for E to produce gray down. 27.6% of gray down chicks were produced from a flock of White Rocks based on e+e+.
In Jeffrey’s experiments, he found that red tints in the down of recessive white chicks apparently had no relation to the gene for gold, since a strain homozygous for silver still produced chicks, 10 percent of which carried red tints in the down.
A conflicting study found that gold in recessive white birds may promote the occurrence of salmon tints in progeny. A strain of White Rocks was found to be .68 for gold and .32 for silver. In the genotype of this strain, 18 percent of the chicks carried salmon tints. By testing and selecting, this strain was brought to a point where it was known to be homozygous for silver. The progeny at this point did not show a single chick with salmon tints in the down.
A study in 1951 pointed towards autosomal red as being a causal factor for red or salmon colored tints in recessive white chick down.
As you can see, while there is scientific research out there for what causes the variance in chick down for recessive white birds, some of it is conflicting. From the research above, we find that the following factors may affect the chick down of recessive white birds:
Extended black (E) allele
Autosomal red
S/S Silver
s+/s+ Gold
co+/co+
Here are a few links to studies to review.
https://www.sciencedirect.com/science/article/pii/S0032579119368932?ref=pdf_download&fr=RR-2&rr=7e817b12995cda67https://www.sciencedirect.com/science/article/pii/S0032579119405646?ref=pdf_download&fr=RR-2&rr=7e8179360d542248https://www.sciencedirect.com/science/article/pii/S003257911951392X?ref=pdf_download&fr=RR-2&rr=7e8179f78ffb2230
