Every alpaca has two copies of every gene (one from dam and one from sire). This also applies to the gene for colour. This is then expressed in the phenotype i.e the colour that you see...obvious so far...what was interesting was the dominance of colours...which is essentially white over fawn over brown over black (greys are another matter).
So a white alpaca may have 2 white genes or may have one white gene and one of another colour, depending on parents, but as white is dominant that will be the phenotype expressed. Therefore if a white alpaca has two white genes it will always have a white offspring, even when mated to a fawn, but the resulting off spring will have one white gene and one fawn (or brown or black depending on the second gene of the fawn and which has been passed on). So the white progeny (from the white and the fawn) is capable of having a fawn, if mated to a fawn ,depending on which gene is passed on.
Unfortunately it isn't quite as easy as this as Dr Merriwether has indentified through DNA testing; a white spot gene and a dark spot gene. It is possible for this to be expressed as masking the underlying colour (i.e one massive spot or sometimes just the extremeties show the underlying colour... for example a brown with a white moustache or foot may be a white with a brown spot gene). There is also a dillutional gene (not so common) that does what it says on the tin.
I did look for some work on the subject on the net and found some work that was done some time ago http://www.alpacagenetics.com/AndyMAlpacaWorldArticle6.pdf however the information presented at WAC was from more recent work completed.
Paul has now come up with lots of theories and is making plans to breed coloured alpacas with fleece qualities of whites...it is a ten year plan (at best depending on whether or not he manages to breed females)...and means that we cannot sell any alpacas until he see the results of his breeding plans...and he calls alpaca breeding MY hobby! I am actually going to let him test his theory, but only on 50% of our females...Cambridge Camilla and EP Cambridge Lady Gaga are definitely in my 50%!
Of course all this relies on the pedigree of the alpacas being correct. During the lecture on Expected Progeny Differences presented by Darby Vannier we were surprised to hear that when the alpacas submitted for the programe were DNA tested, 15% of them had been registered to the incorrect sire!
All of the lectures were packed full of information but some are difficult to share without the photos or notes. Now we are deciding if we can manage to get to the World Alpaca Confernce 2013...in New Zealand...we have had a kind offer of accomodation...so we are very tempted.
Although we have not got a great deal of stock left...we have Our Alpaca Shop up and running. Now to get some more products created...lots of decisions...too many for a Sunday!