Drizzle

part one

By James Gratz dvm

 Larry Long (posthumously)

Introduction: 

In the spring of 2005, Larry Long acquired the first, then unnamed drizzle racing homer, from No Fear Loft, Mike Shippert and Lew Digby, from Dixon and Polo, Illinois.  The mutation most likely is down from Pete Hogan stock. ¹    Originally the bird was thought to be homozygous undergrizzle-Ug.   Undergrizzle in the homozygous state causes a whitening of the basal feather shafts, “Usually the feather is normal color at the tip followed by some bronzing and then white basally.  The effect is most noticeable on the flight and tail feathers.  In the homozygous state, the juvenile feathers are white with colored tips over the entire body and may appear somewhat piebald or mottled in some areas…changes at the first molt so that the covert feathers may make the bird look normal color with the wings closed.”²

Breeding the bird in 2006 caused Larry to suspect something wasn’t right with the thought that it was undergrizzle.  Undergrizzle expresses very little in the heterozygous state, but in this case, more affected birds were produced in the first year.  Larry brought 4 to NYBS and gave me one, a hen.¹   I bred from this hen in 2007 and compared notes with Larry in the late summer after he was diagnosed with cancer.^3,4  I hoped he would write it up.

Experiment: 

I bred the affected hen to a blue bar white flight cock of my own family of racing homers.  I have maintained this family for over 20 years and have not observed any undergrizzle in that whole time period.  I did not breed in an individual breeding coop, but there were no other racing pigeons in the loft where the breeding took place.  The offspring are legitimate as they obviously are not fancy pigeon crosses.

Results: 

The mating of an affected hen to a wild type cock of unrelated bloodline produced nine young that survived to weaning.  Seven of the young were affected.  Only three affected young survived to sexual maturity; two cocks and one hen.  These three offspring have all produced affected offspring.

Conclusions: 

The mutation Larry Long discovered is clearly a dominate or codominate.   Larry named the mutation drizzle, because the birds look like those viewed through a steady rain.³    He also gave it the symbol Drz, as dr was used by Gary Fillmore for drumming.⁵  Drizzle is also an autosomal gene (not sex linked) because a drizzle hen when mated to wild type produced a drizzle hen.

Description: 

Drizzle-Drz, an autosomal dominate or codominate, causes a lightening or a shift from blue to grayish, of the entire bird, both coarse and smooth spread areas.  In some birds, the head and neck are nearly the same color as the body.  The wing bars and dark terminal band on the flights are lightened as well as the terminal tail bar.  Drizzle also causes a whitening of the basal areas of the feathers especially the primaries, secondaries, tertiaries and large tail feathers. There is considerable variation in phenotype from subtle to extreme, but they all are lightened and have basal whitening.  Pictures C-F.

Discussion: 

Seven out of nine affected is higher than the 1:1 ratio expected for a dominate or codominate gene, but seven or more drizzles are expected to happen 8.9% of the time, so not outside expected random chance.⁶  Since the affected can be determined at a young age, some bias may also have been responsible.  The lack of survival to maturity is due to a serious hawk problem and not a lack of viability.

Certainly part of the phenotype looks like undergrizzle.  To date I have not produced any lightened birds that did not have the undergrizzle like effect.  I have also not produced any normal colored birds that had an undergrizzle like effect. 

A similar autosomal dominate gene in Europe, discovered by Bernhard Koellhofer and published by Andreas Boisits, has been named anthrazit-An (anthracite).⁷

Much is yet to be learned about drizzle.  Is it dominate or codominate?  Can homozygous birds be produced?  Is it lethal in the homozygous state?  What, if anything, is it an allele to?  How will it interact with spread, recessive red and other mutations?

References:

1)    Email  1/29/07, Larry Long

2)    Genetics of Pigeons, 2005, Lester Paul Gibson,  page 44

3)    Personal communication with Larry Long

4)    Email 8/09/07, Larry Long

5)     Genetics of Pigeons, 1995, Lester Paul Gibson, page 124

6)    Calculated using the online binomial calculator at site: http://www.stat.tamu.edu/~west/applets/binomialdemo.html

7)     Oesterreichischer Kleintierzuechter 2/2008

Special thanks to Richard Cryburg PhD for his encouragement and help with the statistics.

Drizzle  Update  2012

Introduction:

The drizzle color mutation in pigeons was discovered by Larry Long in 2005.  He found it in racing pigeons tracing back to Pete Hogan “Leen Boers” through No Fear Loft.  Long’s first drizzle was AU 05 NO FEAR 766, “2nd High Point young bird of the year…that flew 9 races.”

Drizzle was named and symbolized (Drz) in 2008 by Gratz and Long.  Long chose the name drizzle because he felt the birds looked like those viewed through a steady rain.  In the 2008 paper drizzle was found to be nonsexlinked or autosomal in nature.  It was also identified as being dominant or codominant.

Drizzle was first described in the Gratz and Long paper as “Causes a lightening or a shift from blue to greyish, of the entire bird, both coarse and smooth spread areas.  In some birds the head and neck are nearly the same color as the body.  The wing bars and dark terminal band on the flights are lightened as well as the terminal tail bar.  Drizzle also causes a whitening of the basal areas of the feathers especially the primaries, secondaries, tertiaries and large tail feathers.  There is considerable variation in phenotype from subtle to extreme, but all are lightened and have basal whitening.”

The purpose of this study is to continue the investigation into drizzle.  Multiple F1’s were produced and mated together to produce F2’s.  Bulging eyes had been observed in a couple previous drizzles, so this was looked for in the F2’s as well.  Since no obvious homozygous F2’s were produced, several F2’s were tested to see if they were homozygous.

Experiment 1:

From the late fall of 2009 through the summer of 2010, 5 pairs of F1 drizzles were placed in a 12’ by 8’ section with a sunporch.  They were allowed to mate at random.  No other pigeons were in the section.  All of these heterozygous drizzles were decedents of AU 2006 ARPU 61941 a daughter of NO FEAR 766.  While all were blue bar and drizzle, other mutations were in the mix as well, including, but perhaps not limited to;  dirty(V), pied genes, and a couple cocks were known to be heterozygous for dilute(d).  None of the birds used had bulging eyes.   All young were banded at one week of age, but no attempt was made to keep track of who the parents were.  It was recorded if there was one or two banded in the nest.

Results 1: 

Forty nine F2 young were banded, all but the oldest 4 were banded consecutively using bands 05/GAR/0705 to 05/GAR/0749.  The color was identified at weaning and double checked at 3-4 months of age after the molt was underway.  While drizzle varies considerably in phenotype, all of the young were classified without difficulty into drizzle or wild type categories.   Based on phenotype none were obviously homozygous.  The lightest drizzles produced were no lighter in color than other drizzles already proven to be heterozygous.   Most were sexed at maturity or necropsy.  Two birds with bulging eyes were identified, one was drizzle and one was wild type.

Results of the 49 F2’s are found in the chart below:

Discussion 1:

Thirty three drizzles and sixteen wild type F2’s were produced.  Using classical Mendelian segregation we would expect a 3:1 ratio if drizzle was a simple autosomal dominant.  With 49 young we would anticipate 37 Drz:12 wild type.  The probability of 16 wild type produced is 0.14, or 14%.  This is within the realm of statistical probability using a 5-95% confidence interval and does not rule out simple autosomal dominance.

Using the assumption that homozygous drizzle is lethal; the Mendelian ratio becomes 2:1.  One lethal for two heterozygous drizzle for every wild type.  With 49 young we would anticipate 33 Drz:16 wild type.This is exactly what was produced, but does not prove drizzle is lethal when homozygous as not enough young were produced to get a statistical result.  Of the two possibilities though, it seems the most likely.  Adding to the lethal assumption multiple eggs pipped but did not hatch.  Unfortunately this was realized too late in the experiment and not kept track of carefully. Fifteen of the young were banded as singles however.  Assuming the nestmate pipped and didn’t hatch the ratio becomes 15:33:16.   This is very close to the 1:2:1 ratio we would expect if drizzle is lethal when homozygous.  Rather than producing another one hundred or two hundred young from the F1 cross, to get statistical proof, another experiment was set up.

Experiment 2:

From the fall of 2010 through the summer of 2011 drizzles produced from experiment one were tested to see if any homozygous drizzle (Drz//Drz) could be found.  All of this testing was done in 2 foot by 3 foot wire bottom cages, with only the test drizzle and a wild type mate present.  Only unrelated birds were used as the wild type mate.  As in experiment one, all birds were racing homers.  If a pair produced 8 to 10 drizzles without any wild type young produced the drizzle test subject would most likely be homozygous drizzle(Drz//Drz).  If one wild type young was produced the test subject would be proven to be heterozygous drizzle (Drz//+).  Once a wild type was produced the pair could be removed from breeding.  The first round of eggs was routinely disposed of.  Consecutive banded birds from experiment one were used to eliminate selection bias in testing.  Twelve of the oldest fifteen were tested. One of the 3 not tested was scalped and died in the breeding cage, one was sterile with two different hens and the third was given away before the experiment started.  Seven cocks and five hens were tested.

Results 2:

From these twelve matings 28 young were produced.  Of the young, 11 were drizzle and 17 were wild type.  The drizzle/wild type distinction was determined at weaning, and verified by a second observer.  Wild type young were produced from every mating.   All twelve drizzles tested were proven to be heterozygous drizzle (Drz//+).

Discussion 2:

The first experiment showed that drizzle is more likely to be lethal when homozygous than it is to be a simple dominant, however that could not be statistically proven.  If drizzle is a simple dominant then one third of the drizzles produced in experiment one should be homozygous drizzle (Drz//Drz).  All 12 tested were proven to be heterozygous, in individual breeding cages.  If drizzle is a simple dominant, the probability of all 12 tested being heterozygous is 0.008.  This result clearly rules out that drizzle is a simple dominant, and proves that it is lethal when homozygous.  Prior to experiment two, several other drizzles had been tested by the author and none were found to be homozygous.  Others have tested possible homozygous drizzles as well.  To the authors knowledge none have been found.

Conclusion:

Previous work by Gratz and Long showed drizzle was not sex linked.  The results in this paper clearly prove with 99.2% certainty  that drizzle (Drz) is an autosomal color dominant, that is lethal when homozygous.

Addendum:

Indigo (I) and dominant opal (Od) are both autosomal dominants that, to a small extent, resemble drizzle (Drz).  In addition dominant opal is lethal in the homozygous.  Crosses to both of these mutations were made.  Indigo drizzle (I//+, Drz//+) and dominant opal drizzle (Od//+, Drz//+) were readily made and tested.  Drizzle was easily proven not to be an allele of either dominant opal or indigo.  Both indigo drizzles and dominant opal drizzles produced wild type young in individual breeding cages.

Only two birds with bulging eyes were produced in this experiment. On e of them GAR 0718 was included in experiment 2.  She has been bred from extensively and has produced drizzle and wild type young with each of several mates.  GAR 0718 is currently blind but otherwise healthy.  It is the authors opinion that the bulging eyes are a separate mutation likely down from ARPU 61941.

By James Gratz dvm

August, 2012 

Additional data on the Lethality of Homozygous Drizzle - submitted by Tim Kvidera, 3/18/2013

Drizzle is an autosomal dominant gene discovered and named by Larry Long shortly before his passing.   Phenotypically heterozygous drizzle is quite similar to heterozygous faded and heterozygous chalky, both of which are sex linked alleles at the almond locus.   Most of the subsequent work with this gene has been done and published by James Gratz, DVM.  From his breeding results James has come to the conclusion that homozygous drizzle is a lethal combination.

This he has demonstrated with a over a 99% degree of confidence by way of multiple matings of drizzles (bred from drizzle X drizzle pairs) paired to non-drizzles and determining that all these young drizzles were heterozygous for drizzle.  If drizzle homozygotes were non-lethal one out of three drizzle youngsters from a drizzle X drizzle pair should be homozygous drizzle.  In breeding from 12 drizzle offspring from drizzle X drizzle pairs Gratz found all to be heterozygous for drizzle.

A few years ago I obtained my start in drizzle from James.  The past two seasons I have been generating data on drizzle X drizzle pairings by monitoring each pair’s egg performance and young bird production.  My results support homozygous drizzle as being lethal.

In 2011 I had one pair of drizzle X drizzle.  They generated six eggs resulting in 3 drizzle youngsters, 2 blue bars and one dead embryo.  The egg candled as being fertile, partially developed and failed to pip or hatch.

In 2012 two pairs of drizzle X drizzle matings were done.  18 more eggs have been classifiable.  Five of these candled as being fertile yet failed to hatch.  Death of the embryo varied from a few days after fertility was confirmed to late term.  One of the 18 eggs showed no indication of having been fertile.  The other 12 eggs produced nine drizzle youngsters and three non-drizzles. 

In summary  -  my drizzle X drizzle pairings have resulted in 1 infertile egg and 23 fertile eggs.  These 23 fertile eggs resulted in 6 dead embryos and 17 squabs (12 drizzles and 5 non-drizzles).  These results (6:12:5) are consistent with a 1:2:1 ratio and support the conclusion that homozygous drizzle is lethal.