"Coloured" vs. White (Sheep Colours as it relates to my flock - Part 2)

You may have noticed that in discussing moorit, I have by-passed white. This is because the genetics that affect whether a sheep is white or coloured involve different loci (plural of locus) than the question of black vs. brown!

There are two main loci that I need to mention in this post:
~ A-locus
~ E-locus


E-locus

I want to deal with the E-locus first.

There are two main alleles at the E-locus that are of some interest to me:
~ The dominant allele at the E-locus is often termed "dominant black", and produces a solid coloured sheep - that will be either black or moorit, depending on it's B-locus alleles. This "dominant black" over-rides the expression of A-locus alleles.
~ The recessive allele at the E-locus allows the expression of the A-locus.

As far as I am aware, I do not have the "dominant black" in my flock. I really do not know for certain if this allele is in any sheep in New Zealand, but I suspect that it may well be in NZ in some of the more exotic breeds that have been brought into NZ in more recent decades.


A-locus / Agouti locus

The main reason that the E-locus is of any interest to me, is that it involves the concept of "colour" over-riding white. In contrast, with A-locus alleles, the usual rule of thumb is that white is more dominant...

There are quite a number of alleles believed to exist at the A-locus. The A-locus / Agouti locus is often called the "pattern locus". The word "pattern" is very important as it is not a matter of which colour, so much as "which pattern" - with different patterns featuring different amounts and locations of white & colour!

The most dominant A-locus allele seems to be one that makes a totally white sheep. The most recessive seems to be one that produces a totally coloured sheep.
 In between those ends of the spectrum, many of the A-locus alleles are "incompletely dominant". So, for the most part, when a sheep inherits two different alleles, it will display the white markings from both alleles!

I'm not clear on all the A-locus alleles in my flock - though there are some very striking colour patterns that I know I have never had! A sheep that came into my flock a few years ago seems to have introduced an allele that I didn't have immediately prior, as I've seen certain distinctive characteristics that I've not noticed before.



Photos:

These  first two photos show white ewes with their lambs. Both of these ewes carried a coloured A-locus allele, and both of them carried one moorit allele (& one black allele) at the B-locus. In both of these cases, the sire was coloured (so had two coloured A-locus alleles), and moorit (so had two alleles for moorit at the B-locus). Thus the sires passed on coloured A-locus alleles and moorit B-locus alleles to all the lambs
 

This photo is of a moorit ewe with a white lamb and a moorit lamb. The sire of these lambs was white, but carried a coloured A-locus allele, as well as having both black and moorit alleles at the B-locus.

This photo is of a black ewe (that did also carry moorit at the B-locus - a fact I know for two reasons - firstly, her sire was moorit, and secondly, she later had some moorit lambs). The sire of her lamb was white, and would probably not have carried any coloured A-locus alleles.

This final photo is a bonus for yesterday's post about moorit. It shows some shorn sheep - a darker-coloured moorit ewe (left), a lighter-coloured moorit ewe (centre), and a black ewe (right), as well as a white ewe behind the others (and possibly a woolly lamb tucked in there too). It gives a good comparison of the colour differences between moorit & black!