As I know several genes (like: brown, scarlet, white,...) affect on the eye color in Drosophila melanogaster. On the other hand, eye color in Drosophila was explained as multiple allele inheritance at different references. I will be glad if someone can explain it to me.
Pigments are transported by the so called ABC transporters. There are two in D.mel.: white+scarlet for brown pigments and white+brown for red ones. Therefore, scarlet and brown double mutants are white eyed. Most other genes involved in eye pigmentation effect synthesis of either red (e.g. rosey) or brown (e.g.cinnebar) pigments. Last, but not least there are some mutants affecting vesicle transport (e.g. ruby).
The eye color of a D. melanogaster is the sum of different pigments (with different concentrations). There are two pathways : pteridines (GTP) and ommochromes (Tryptophan).
-> Pteridine => Biopterin (blue) => Drosopterin (red-orange)
=> Dihydropterin (blue)
=> Xanthopterin (yellow-green) => Isoxanthopterin (purple)
=> Sepiapterin (yellow-orange)
-> Ommochrome => Cynerinin => Hydroxanthommatin => Xanthommatine (Brown)
This genes are located throughout the genome of D. melanogaster. Each step of the pathway is catalyzed by a separate enzyme, if an enzyme is not produced (or not functional) like a mutation, the pathway is halted.
Useful visual of above points:
http://www.indiana.edu/~oso/lessons/Genetics/bw_st.html
I started studying Drosophila eye colors over the summer and have found that the phenotypic consequence (i.e. eye color) of combining a mutation in the pteridine pathway (besides brown) with one in the ommochrome pathway is often difficult to predict. Besides doing the crosses empircally, does anyone know of a published resource on this topic?
I've been suprised by some results such as the persistent pale orange color of v;bw flies (that darkens with age), which should phenocopy bw;st and cn bw.
Arvind, mutations in white are epistatic for the reasons that Burkhard has indicated. As Chlasta and Burkhard have explained, white is required to transport guanine and tryptophan into the developing eyes during pupation so that the ommochromes and pteridines, respectively, can be synthesized; as a result, white sits at the top of the eye color pathways, so mutations to w will usually alter the eye color, regardless of mutations to other eye color genes.
Mark,
there is a recent book: "Atlas of Drosophila morphology: wild type and classical mutants" by Chyb and Gompel that has very nice pictures of the most common mutants used as markers. In some cases they even show young and aged flies, as some eye colours darken with age.
It is a beatiful and very useful book!
Free and valuable resource from the Kaufmann lab:
http://flybase.org/static_pages/images/posters/EyeColors.pdf
No double mutants however...
http://flybase.org/static_pages/feature/previous/articles/2013_02/mutant_images.html
Thanks Bàrbara and Thomas. I have accessed the high resolution pictures available on flybase before; the double mutants have sometimes been very surprising, especially as they age.
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