The Parblue Puzzle

Part 5 — Uncertain Conclusions

Much to Learn

From the foregoing sections it can be seen that where Blue and Parblue varieties occur in a parrot species they invariably present a complex and puzzling genetic situation. Differences between species seem to rule out any single all embracing genetic model. However, the indications at present are that in all cases only one gene is involved and that this gene is quite prone to mutation and the consequent formation of a multiple allelic series. It is the hierarchical structure of relative dominance within the series which appears to differ from species to species.

This should not blind us to the fact that the biochemical pathway which finally produces psittacin pigment will comprise many steps, or stages, at which biochemical processes occur and each one of these will be under genetic control. For a bird to appear ‘normal’ each of the steps must confirm exactly to the plan ordained by the gene complex which has evolved over the millennia for that species. There is always the chance that another gene along the psittacin producing biochemical pathway will mutate to produce a completely separate and distinct Blue or Parblue variety. The situation would then get really complex.

Leaving aside this possibility, there are already a number of complicating factors which might make the task of unravelling the genetics of the varieties we are discussing quite difficult. These include:

• Relatively small variations in psittacin concentrations can be caused by a number of minor modifying genes (polygenes). By selective breeding these may be accumulated and fixed, to produce strains or lines significantly paler or deeper than the rest.
  
  
• Similarly, birds from different parts of the geographic range of a species may have been taken into aviculture and have naturally occurring concentrations of polygenes producing the same effects.
  
  
• These effects may, in both instances, be enough to mask or blur the effects of the major colour genes we have been discussing.
  
  
• Where two genes do control the same characteristic, it is not unusual to find that they lie closely together on the same chromosome. These very tightly linked genes nearly always act as one, passing together from generation to generation in their original combination, and have been christened supergenes. (It can be argued that it is advantageous to an organism for its genetic structure to develop in this way.)
  
  In some instances where multiple alleles are first suspected it is later found that the effects are due to distinct and separate genes which, as described above, lie very closely together on the same chromosome.
  
  
• Where alleles of two separate and distinct genes control the same characteristic they can interact in many different ways to produce two or more visual types in unusual proportions. These proportions would be further modified if the two genes were linked.
  
  
  

These points are made to urge some caution in interpreting breeding results. However, the reality is not likely to be this complex and experienced breeders should be able to piece together the genetics of the Parblue varieties over a reasonable period of time. Every breeder of these varieties, no matter how many birds are bred, has the opportunity to play a part in solving the puzzle.

This is just one of many opportunities for committed and enthusiastic breeders to rise to the challenge of extending our knowledge. A chance to make a mark in avicultural history. All that is required over and above the usual avicultural skills are an eagerness to share the knowledge gained as an individual, methodical and precise record-keeping, a basic understanding of genetics, and the ability and self-confidence to write and put forward a written report or account.

These days the popular avian press seems reluctant to publish articles deemed too taxing for their readership. All part of the dumbing-down process overtaking our culture. However the Newsletters and Magazines of the various Societies associated with aviculture, and Websites such as this, should have a much more positive attitude and credit their readership with more than a superficial interest.

Copyright: Clive Hesford, 1992 and 1998

Bibliography

Smith, G. A. 1992. ‘The Turquoise or Parblue Ringneck’, Parrot Society Magazine (UK); April 1992.

Hayward, J. 1992. The Manual of Colour Breeding; Avicultural Publications, Oxford, UK.

Grey, K. H. 1990. Rainbow Budgerigars; Essex Rainbow Publications, Clacton-on-Sea, UK.

Zomer, H. P. M. 1989. Grass Parakeets and their Colour Mutations; B.E.K. Publications, Dorchester, UK.

Taylor, T. G. & Warner, C. 1986. Genetics for Budgerigar Breeders, 2nd Edition; The Budgerigar Society, UK.

Ford, E. B. 1979. Understanding Genetics; Faber & Faber, London, UK.

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