Robinson (1989) reanalysedThis article was written by Sheila Sowter for Pro-Rat-a in 2009. She has kindly given me permission to publish it on my web page.
It is twenty years since Robinson (1989) wrote his paper describing a new allele (he) of hooded white spotting and since then more alleles on this H locus have been discovered. Robinson's paper has no pictures or diagrams but his verbal descriptions suggest an interpretation of the data different from his.
Robinson was supplied with breeding animals of white variant which were interbred. He notes that though the eyes were dark they appeared dark red in strong light and though the animals were white some were not completely so but might have some spots of colour on the side of the head. This sounds like a description of present day black eyed white (BEW) which also tends to have stray spots of colour and the appearance of deep ruby eyes even when derived from black eyed stock. A contemporary description of breeding BEWs by Wildman (1989) says they were then still not breeding true, mentions the very deep ruby eyes and the use of a "mismarked mink capped" in one of the matings giving six kittens including three BEWs two of which later marked up. Wildman (personal communication) was, at the time, working with and exchanging stock with the suppliers of Robinson's stock.
Modern BEW's are thought to be HRohc where HRo is the Robert gene and hc the gene which when homozygous gives capped (Sowter 2009).
Robinson mated his white variant to homozygous self coloured (no specific colour mentioned) and apparently assuming that his white sample must be homozygous on the H locus classed all the 29 offspring (line 1, table 1) as a single phenotype but with a variable expression which he called "roan".
The head is usually solid coloured but the body fur is a mixture of white and coloured hairs. The expression is variable [my italics], ranging from individuals with solid coloured dorsums but with roan coloured venters, to individuals with extensive roaning all over the body. A suggestion of a "hooded" pattern may be shown by a lessening of the roaning along the spine. The more extremely roaned animals have completely white stomach fur and there may be some inversion of the solid coloured head by white hairs.(Robinson 1989)
If this white variant was HRohc he would have got HHRo Robert (Essex) and Hhc. The second part of his description fits the Robert (Essex) (extensive roaning, lessening along the spine, white stomach fur), the first part (solid coloured dorsums) fits the irregular Berkshires Hhc (Sowter 2009) which can have bellies that are almost spotty.
Robinson gives a table of his results. Line 1 is white variant hehe with self and all offspring given as "roan". Line 2, +h x hehe shows 14 of the 86 offspring as "hooded". Obviously these could not be hh hooded but might be the hhc hooded-ish (Sowter 2009). The 46 roans would be HHRo and Hhc and the remainder baldies HRohc and hhc where the vestigal saddle was absent. Line 3 records interbreeding of roans but we cannot know which type. Similarly in line 4 hhe, though we cannot know what was used, of the 217 animals produced we would expect 50 or so to be hehe yet not a single white animal is recorded and only 24 with white head and some coloured spots. Line 5 records interbreeding of the white variant. If it were hehe all the offspring would be hehe, BEW or near BEW. If it were HRohc the offspring would be HRohc and hchc in proportions 2:1 since HRoHRo is lethal. The sample size is small (92) but 38 have considerable colour on their head seeming not to be near BEW.
I have suggested that Robinson was not working with homozygous animals but with HRohc. Is there more evidence to support this? It was not until 1997 that the Robert gene was characterised (Sowter, 1997). One of the consequences was a stream of people coming to me with rats of unknown origin for me to identify. It was obvious that the gene was then widespread in the pet rat population. HHRo were "Berkshires" with unusual colours and poor demarcation. HRoh was taken for capped and indeed still turns up on the show bench in the capped class. In many cases it is difficult to differentiate between hchc and HRoh without test mating. In the same year as Robinson published his paper, the NFRS handbook (1989) describes BEW breeding which used and produced capped (Wildman 1989) and in the section on capped Ann Storey (1989) said "try not to breed rats with big blazes" (quite possibly baldies) "as this feature tends to get worse very quickly. In fact two rats with only small spots may breed a complete litter of almost white faced rats". [my italics]. Capped rats which are homozygous give only capped rats when interbred.
In summary, Robinson's white variant was probably HRohc and the he allele which when homozygous gives BEW does not exist.
Robinson, R. (1989) An extreme allele of hooded spotting in the Norway rat. Genetica 79, 139-141
Sowter, S. (1997) The Robert gene, Pro-Rat-a 99, 10-11
Sowter, S. (2009) The Capped gene, Pro-Rat-a 171, 17-18
Storey, A. (1989) in National Fancy Rat Society Handbook pp. 41-42
Wildman, D. (1989) in National Fancy Rat Society Handbook pp.38-39