Multiple Alleles and Bengalese Colour Inheritance

This is an extract from a post made by the late Mark Shipway in the BBS Yahoo Group on 11/10/2001, and definately has some worthwhile points to consider.


"I am in the midst of preparing some ideas about standards and types.  As a starting point I thought I'd prepare the ideas below about bengalese colour.  Please bear in mind that this is a theory I have developed and have based it on my experiences and what I have read in other articles, journals etc in foreign magazines on Bengalese.  I have no scientific data to back my conclusions and am prepared to accept that some of my views are open to challenge.  Having said that I believe that this information forms the basis of what we do know to date about bengalese colour.
I believe its important we know about bengalese colour before we go about developing colour standards.  There is also a picture for you to view.
To report on breeding progress.  I have some young in the nest from a large pied cock (source Deon) to a small self hen.  So I am one step closer to producing larger selfs.
Feelfree to make comments on the information below.


Part 1 - Feather colour in Bengalese
Feather colour in Munias is produced by melanin. Two types of melanin occur in Bengalese,namely:
·      eumelanin
·      phaeomelanin
Eumelanin
Eumelanin canbe either black eumelanin or brown eumelanin. Chocolate Bengalese have both. The "Euro" bengalese is effectively a bird with extensive black melanin caused by both selective breeding and introduced from hybridisation with birds with high amounts of this type of melanin e.g.. Blackheaded nuns.
Australian Chocolates show black eumelanin in the face and to varying degrees down the throat to the breast and on the wings and tail. Brown eumelanin is evident almost everywhere. Chestnut Bengalese have some brown eumelanin but no black eumelanin.
Eumelanin in its purest form is the grey mutation.
Phaeomelanin
In its purest form, the fawn bengalese shows virtually only Phaeomelanin. The fawn bengalese should really be called a "phaeo" rather than fawn, cinnamon, ginger or red brown. It is not a true fawn mutation like say the fawn Zebra finch. The only example of a true fawn/cinnamon mutation in munias in Australia that I am aware of is the Fawn Java Sparrow.
Both chestnut and chocolates, like fawns, have varying degrees of phaeomelanin.
A bengalese without any eumelanin or phaeomelanin is white.

Chocolate has the following melanin:
·      Black eumelanin
·      Brown eumelanin
·      phaeomelanin
The future objective with the colour of this mutation should be to increase the amount of black eumelanin.

Chestnut has the following melanin:
·      Brown eumelanin
·      phaeomelanin
The future objective with the colour of this variant should be to settle on the ideal shade and focus on improving its evenness.  I believe that the chestnut should be a grade half way between the chocolate and the fawn.

Fawn has the following melanin:
·      phaeomelanin
The future objective with the colour of this mutation is to darken up the phaeomelanin as much as possible so that it matches Dutch red browns. I believe some individuals are almost there.  I am not sure whether the increase in black melanin in chocolates will assist to intensify the phaeomelanin, time will tell here as we experiment further.

Dilutes are really pastels which have a quantitative reduction in both eumelanin and phaeomelanin to varying degrees between individual birds. It is for this reason that it is not correct to call a "chestnut" a chocolate dilute because, whilst there may be some reduction in eumelanin, there is no reduction in phaeomelanin.

Colour variability between individual birds of the same mutation
Within any particular colour variety it is apparent that intensity of colour varies between individuals. This is particularly relevant in the chestnut mutation (possibly because there is high variation in brown melanin) which has given rise to my confusion in the past as to whether two particular birds are different shades of chestnut or are two different mutations. This is what brought about the name "smokey" and "cream" but I now see these names as not relevant.
Why is this? The most probable explanation for colour variability in bengalese is the effect of multiple alleles. Unlike most other species of birds, in bengalese an unknown number of alleles control colour. They all share the same position onthe chromosome but only two can occupy the position in any particular individual bird. Some combinations result in darker colour whilst others resultin in light colour in graduations down to a colour regarded as dilute.

Multiple Alleles
It is importantfor a bengalese breeder to understand what multiple alleles means and how it operates because it is central to the relationship between:
·      Chocolate, chestnut and fawn
·      The intensity of colour within any particular colour variant
·      possibly, the relationship between pied birds with varying amounts of white.
On the latter point, more research is needed to be sure. I have made this tentative conclusion based on incomplete past breeding experiences.
Chocolate, Chestnut and Fawn
On the basis of multiple allele theory, chocolate is dominant over chestnut and fawn. Chestnut is dominant over fawn. No chocolate can be split to both chestnut and fawn. The only way to produce chocolates, chestnuts and fawns in a particular nest is to mate a Chocolate/ fawn to a chestnut/fawn. Please view the attached photo ofthe three mutations side by side. The fawn can be distinguished from a chestnut on the basis that eumelanin remains in the bill and legs of the chestnut. There is little, if any, phaeomelanin in the bill and legs of a bengalese.
End of Part 1


Kind Regards
Mark Shipway"