🚀 go-pugleaf

Hi all,

Whew, I had a feeling my first publishing would be about my rats, and would be
in usenet forum.

But I thought it would be regarding disease in Australian rat colonies.  

It seems fitting for it to appear here, in this developing aus.science
newsgroup.  Please excuse my unfamiliarity with the publishing protocols.

But here goes:


The Presence and effects of the dominant Pearl gene in Australian Fancy rats.
L "Ana" Farrall.


Background:  

The show standards for Fancy rats in Australia has been under development for
five years.  For the last two, they have been "stable", but the genetic
information relating to some of the standardised phenotypes has been awaiting
research.

There has, however, been variation in several colours which has caused them to
be considered "guide standards".  These are Dove, Pearl, Cinnamon, and Topaz.


Materials and Results:

Rats from my own mischiefs, exhibiting phenotypes typical of standardised
phenotypes in other countries, bred to assist development of Australian
Exhibition standards in what is now referred to as Rattus douglasii, because of
their distinct differences to the wild Norway or Brown rat.

Mink, aamm, and Dove, which is the expression of the Red eye gene (rr) on mink.
(aammrr) having been bred for three and four generations to establish a good
Dove colour for exhibition and Pearl rats, also for exhibition.

Lines of the highly irregular "topaz" which was theorised to possibly be a ruby
eyed Cinnamon (A/-mmrr) or ruby eyed Agouti (A/-rr).

Cinnamon, Argente and Topaz rats which had been bred for four and five
generations, to establish what the genotypes of Argente and Topaz are, and their
possible relation to the Cinnamon A/-mm and Mink aamm genotypes.

In the fourth and fifth generations, five does bred to bucks for this purpose,
appeared to spontaneously abort.  100% of the litters were lost.

Robinson identified definite links between the expression of the dominant Pe
pearl gene in combination with homozygous recessive mink (aamm) and heterozygous
Agouti Cinnamon (Aamm)

	He observed that Pepe caused two types of phenotype.  One, the Pearl of
UK and Australian standards, which is a very pale, almost white hair base, with
dark "tipping" of the hair.  The pearl Pepe was observed to produce a greatly
varying phenotype, between a light dusting and a profusion of tipping heavy
enough to imitate a "roan" colouration.

	The second he called "yellow pearl" as it had a similar tipping effect
on the hair, but in combination with the golden or red banding of the hair,
associated with the phenotype of a dominant agouti gene. This is the genotype
now referred to as Cinnamon Pearl in show standards.

	Pearl is dominant to mink and hypostatic to other genes.  It can only be
expressed in combination with homozygous mink genes.

	The Cinnamon pearl was observed only in heterozygous dominant agouti
rats: AammPepe

	It was also documented that homozygous dominant PePe pearl is a lethal
gene.


Discussion:
	
If "topaz" is the same genotype as the "lynx" or "lilac agouti", which was
proposed because of the similarity in the phenotype, and the great variations in
the phenotype, then the genotypes would be A/-ddbb and A/-ddbbrr.  

If this were the case, then in breeds and line breeds for A/-dd and A/-bb
colours, as well as chocolate aabb and blue aadd should result.  These genotypes
have not been observed in Fancy rats in Australia.

Following comparison of my own breeding and the observation of great variation
in the appearance of the "topaz", together with the unexpected loss of line bred
litters, it appears that the "topaz" is actually the genotype A/-mmPepe which
Robinson identified as the Agouti "version" of the pearl and mink.

Robinson also observed that all his Cinnamon Pearl rats were observed in
heterozygous agouti genotypes, hence the homozygous agoutis could be carrying a
heterozygous mink recessive Mm and a heterozygous Pearl dominant Pepe, without
expressing either colour, it would appear as a normal Agouti phenotype.

Given the expression of pearl phenotype only in combination with homozygous mink
and heterozygous agouti, it would be expected that line breeding to produce this
phenotype should appear in 50% of the breedings of rats known to be carrying
both an Aa agouti, mm mink, and Pepe pearl dominant. 

This result, however, was not observed.

100% of the 5 litters bred to exhibit the Pe gene in the aammPepe and A/-mmPepe
phenotypes failed.  At the time, it was considered that a pathogen was likely to
be responsible for the losses.  In particular the Sendai virus.  

However, three of the does who lost litters had been bred before, and the only
fatalities were 2 aged rats.  It is still possible that a pathogen contributed
to the losses of litters, but normal Sendai symptoms would be for only does
carrying their -first- litter to be at risk of spontaneous abortion.

It could be possible that some of the rats bred actually carried homozygous PePe
genotypes, which weren't able to express the lethal effects of the gene, because
of the lack of a homozygous mink mm to combine with or a heterozygous agouti Aa.

Robinson doesn't comment on this possibility, since he was breeding from rats of
known genotype.

Now that the genotype of the formerly described "topaz" rats, with the great
variation of phenotypical effect of the Pepe pearl gene causing the variations
in seen in the "topaz" rats, it can be assumed that the "topaz" phenotype is
actually Cinnamon pearl AammPepe.  


Conclusions:

That great care should be taken in line breeding for Pearl phenotype rats, due
to the lethal nature of the homozygous dominant genotype.

That further test matings of Cinnamon pearl and mink rats be undertaken to
provide data for the supposition that there is a possibility of AA and Mm
genotypes to successfully "carry" a homozygous dominant PePe.

That Australian Standards for the exhibition of Fancy Rats be ammended to list
"topaz" as AammPepe Cinnamon Pearl, and "Argente" to be test bred to
substantiate the probability that this phenotype is actually A/-rr, a red or
ruby eye dilution of Agouti.


References:

Roy Robinson, "Mink and Pearl: New colour mutations in the norway rat."  in the
Journal of Heredity 1994:85(2) pp 142, 143.

NFRS Standards of Excellence.  NFRS 1999.

History of Standards, Nick Mays, NFRS archivist, in conjunction with the
Standards of Excellence.