Coming from scientific backgrounds, we have always believed that applying some basic genetic principles to our breeding program will greatly enhance the rate of improvement within the herd and help avoid some costly disappointments. This has been of particular importance to us in our quest to build a herd of white suris which breed true to type, and because of our interest in cross-breeding suri with huacaya. We are always happy to try to explain the science of genetics to those entering the industry, for whom it may seem a daunting subject full of technical terms.

Here are three brief concepts which may be helpful:

1. Sex

The sex of any individual (be it human or alpaca) is determined by their sex chromosomes. Like all other chromosomes these occur in pairs. However, the key difference is that females have two of the same type of chromosome, called X, whereas males have two different sex chromosomes, one X and one Y. When the chromosomes divide to form the female’s egg cells, every egg must therefore carry an X chromosome—she has no other type. During the production of the male’s sperm, however, the chromosomes will divide and 50% of the sperm cells will be X and 50% will be Y.

	The end result is that 50% of offspring will be female and 50% will be male
	Since the female can only contribute X chromosomes, while the male can contribute X or Y, it is technically the male that is determining whether the offspring will be female (XX) or male (XY). Although some breeders claim that environmental factors (drought, diet etc) or the receptivity of the female’s egg cell to one type of sperm cell can lead to more of one sex than the other being produced, to us this seems highly unlikely. At the end of the day it all comes down to random chance, the toss of a coin, and if one looks at the progeny produced in a herd over a number of years, or at a number of herds during any one year, there will be a 50:50 split between the sexes
	When selecting a female, therefore, treat with due caution any claims by her breeder that “she’s always given us girls” or “she comes from a whole family of females who only ever breed girls”. Whilst this may indeed be the case, it is only because, to date, they have been lucky!

Unfortunately the inheritance of sex in your alpacas is something over which you have NO CONTROL.
You get what you are given!

2. Colour

Unfortunately for all alpaca breeders the inheritance of fleece colour is not a simple matter of one colour gene being dominant to another. There are numerous theories, but all agree that there are both colour genes (e.g. black) and modifier genes, which can cause multi-colouring, spots or dilution of the main colour to a lighter shade.

So, where does this leave the poor breeder attempting to produce their chosen colour line? The following pointers may be helpful:

	Use the AAA database to study the colour of progeny that the male you are considering using has produced. Does his colour tend to dominate when he has been mated to different coloured females? Does he tend to produce a lighter or a darker shade of the female’s colour? What colour were his ancestors and his siblings?
	Don’t forget to research the colour background of your females as well—remember, they are contributing 50% of the genetic make-up of the cria they produce. What colour were her ancestors and siblings? What colour cria has she previously produced and out of what coloured male?
	You have the best chance of producing a certain colour if you mate two alpacas who are that colour
	White animals often seem to be carrying coloured genes and if a white is mated to a colour the progeny are more likely to be coloured than white. A mating between two coloured alpacas will almost always result in some form of colour, rather than white
	Many otherwise solid-coloured animals (including solid whites) will have a spot of another colour somewhere on their body. This may serve as an indication that they are carrying that colour

The inheritance of colour, therefore, is something over which you have SOME CONTROL, through careful breeding decisions.
But there will always be surprises!

3. Suri and huacaya fleece type

The gene controlling whether an alpaca’s fleece type is that of a huacaya or suri is an example of “the law of genetic dominance”. The gene which produces the suri fleece type is dominant to that which produces a huacaya fleece type.

This means that in order to have a huacaya fleece an animal must be what is termed “homozygous” for the huacaya gene—this means that they are carrying two huacaya-fleece genes. If you mate one huacaya alpaca to another, there can be only one possible outcome—a huacaya cria.

BUT, if you are breeding suris, life becomes a little more complicated...

Some suris will be carrying two suri fleece type genes and, of course, these animals have a suri fleece—they are “homozygous” for the suri gene. However, because the suri gene is dominant it means that some suri alpacas will be carrying one suri gene and one huacaya gene and although they look exactly the same as homozygous suris, they will pass on their huacaya gene to 50% of their offspring. These suris are referred to as “heterozygous”.

The issue of whether a suri is heterozygous or homozygous can be extremely important for the breeder, as the following facts demonstrate:

	If two homozygous suris are mated together, 100% of their offspring will also be homozygous suris, carrying only suri genes
	If a homozygous suri is mated to a heterozygous suri, 100% of their offspring will be suri in appearance (or “phenotype”) but 50% will be heterozygous and carrying the huacaya gene
	If two heterozygous suris are mated together, 75% of their offspring will be suri in appearance but one in four progeny will be born huacaya, which can be very disappointing for the dedicated suri breeder. In addition, two out of every three suris produced will, like their parents, be heterozygous and carrying a huacaya gene which they may pass on to future generations. Only one in every four progeny produced from such a mating will be a homozygous suri which can be guaranteed to breed true to the suri type
	If a huacaya female is mated to a homozygous suri male, 100% of the offspring will be suri, but all will be heterozygous as they will have inherited a huacaya gene from the dam and a suri gene from the sire. These cross-bred suris are known as “first-crosses”, often abbreviated to “F1s”
	If a huacaya female is mated to a heterozygous suri male, only 50% of the offspring will be born as F1 suris; the remainder will be born huacaya, having inherited a huacaya gene from the dam together with the “hidden” huacaya gene being carried by the heterozygous suri sire. Given that breeders really only use cross-breeding as a way of producing F1 suris, this is not a good result!

So, if you are thinking of breeding suris bear in mind a few key points:

	The only way to guarantee you will never produce a huacaya from a suri/suri mating is to be certain that at least one of the parent animals is a homozygous suri. In practice, it is usually easier to prove this with a male, as they have the ability to produce many progeny each year of their productive lives
	If you plan to produce F1 suris by crossing huacaya females with a suri male it is essential the male is homozygous, or you will produce only 50% suri offspring
	If you buy, or breed, F1 suri females, you would be wise to mate them with a proven homozygous suri male to produce your next generation (known as a back cross 1 or BC1). If you use a heterozygous suri male you are crossing two heterozygous animals and therefore one in four progeny is likely to be a huacaya

How do you know if a suri male is homozygous?

The best way to test a male is by mating him to a number of huacaya females. If out of ten such matings you only produce suris, you can be 99.9% sure the male is homozygous; even five matings producing all suris will give you a 96.9% certainty. However, as soon as the first huacaya cria is born, you know that the male is heterozygous and carrying the huacaya gene.

Why cross-breed at all?

You might wonder, given all the above, why anyone would ever attempt to cross breed suri and huacaya, and there are breeders who understandably take the decision to keep their suris “pure”. At Birrong we decided, at the outset, to experiment with cross-breeding for the following reasons:

	Cost—high quality suri females are expensive. Cross-breeding good quality huacaya females with good quality homozygous suri males is a way of producing affordable suris
	Availability—even if you are prepared to pay a high price, good quality “pure” suris are relatively scarce
	Colour—it can be difficult to access reliable coloured (including solid white) genetic suri lines. Crossing proven coloured huacaya lines with suris is a way of importing these colour genetics into the suri population
	Hybrid vigour—the majority of cross-bred animals will be particularly robust and fertile, and may combine the best features of the two pure types

But there are disadvantages:

	It can take several generations, and therefore years, to produce top-quality suris having a good likelihood of being homozygous for the suri gene
	It is very unwise to mate two F1s to each other (this would produce an animal classified as an F2) as there is a 50% likelihood of reverting to the huacaya type
	Male F1s, whilst they may be good for fleece production or showing, should not be used for breeding as they are, by definition, heterozygous

In the end, it is the breeder’s personal choice whether to cross-breed or attempt to keep the suri line “pure”. You do, however, if you understand and adhere to the genetic principles described, have RELATIVE CONTROL over the outcome of your breeding decisions.