Part Two

Remember part one? The key terms introduced were a few of the basic horse colours (grey, bay, black, chestnut) and homozygous and heterozygous. Genes are located on loci (location..loci, easy enough to remember) and on each locus (locus is singular for loci), there are two genes for each trait. With horse colour genetics, a trait for example can be grey versus non grey. On the grey locus, there can be one copy of the grey gene (written as G) and one copy of the non-grey gene written as g, so the horse genetically is written out shorthand as Gg.

A horse homozygous for the grey gene would be written out as GG. A heterozygous grey horse would be written out as Gg.

Now to understand how we go from this shorthand written out to how your horse actually appears, a short introduction to dominant versus recessive genes is needed.

Dominant traits only need one copy of the gene on the locus to be expressed. For example, grey is a dominant trait. A horse only needs to be heterozygous for grey and posses one grey gene to be grey coloured. A Gg horse will always appear grey coloured.

Recessive traits need two copies of the gene to be expressed. Non-grey (g) is recessive and for a horse not to be grey, it needs two non-grey genes (gg) and homozygous to not express the grey gene.

For the genetic shorthand, there are certain standard letters to represent colours as shown below and will be expanded upon as we continue our journey. For now, just the colors we have discussed will be represented. Each line signifies a locus and has the gene and the opposite gene of that trait (ie grey versus non grey). The dominant gene is written first and is always expressed with a capital letter.

Grey (G)---Non-Grey (g)

Black (E)---Chestnut (e)

Bay [Agouti] (A)---Non-Bay (a)

I know a lot of terms have just been thrown at you and I admire the persistence if you made it this far, but trust me, it'll get easier once you understand the basics.

Get up, have a stretch, a cup of coffee, pet a horse, and come back when part three is written.