With special thanks to Birrong Suri Alpacas Australia
Suri Alpaca Genetics Made Simple
(or how to win at cards!)
To be successful in breeding any livestock, be it cattle, sheep, horses or chickens it is vital to have at least a basic understanding of genetics. This was never more the case than with breeding the suri alpaca. Genetics is the science behind the art of livestock breeding. Without this knowledge the breeder will find it very hard, if not impossible, to make informed purchasing decisions and ensure that each generation of breeding shows an improvement on the previous. Sadly, it is a topic which is often put in the “too hard basket” by many new (and not so new) suri alpaca breeders leading to disappointment and disillusionment.
What is Genetics?
Genetics is the study of heredity and the units of inheritance (genes) which are contributed equally by each parent when they mate and produce offspring. One of the most off putting things about beginning to study genetics is the baffling terminology, and we will try to explain some of the most important of these concepts in the simplest way. Most of us will understand a little of how blue or brown eyes are inherited in humans and we have used this as an example throughout the definitions:
- Gene: A gene is a unit of inheritance which will cause a particular characteristic in an individual, such as eye colour. Most higher organisms (including humans and alpacas) have two copies of each gene. These two copies may be identical or may be different to each other
- Homozygosity: If the two gene copies are the same, then the individual is said to be homozygous for that gene. A person who has two genes for blue eyes is “homozygous for the blue eyed gene”
- Heterozygosity: If the two gene copies are different, then the individual is said to be heterozygous for that gene. A person who has one gene for blue eyes and one for brown eyes is “heterozygous for the eye colour gene”
- Dominance: This is one of the most important concepts in genetics: some genes will always show dominance over others. So, the gene for brown eyes is dominant over that for blue eyes in humans. This means that an individual who is heterozygous for the eye colour gene will have brown eyes, even though they are also carrying a copy of the blue eyed gene
- Recessive genes: A gene which is not dominant is termed recessive. In order for a recessive gene to show itself in the appearance of an individual, that individual must be homozygous for the recessive gene. Thus, because the blue eyed gene is recessive, for a human to have blue eyes they must be carrying two copies of the blue eyed gene – they are homozygous for the blue eyed gene
- Genotype: This term is used to describe the exact genetic make-up of an individual, e.g. whether they are homozygous or heterozygous for a particular gene, such as eye colour. An individual’s genotype can never be changed – you are born with a set genetic blueprint. You cannot see an individual’s genotype, but you may be able to deduce something about it by studying their family tree or pedigree
- Phenotype: This is what you actually see in front of you – the person with brown eyes or the alpaca with suri fleece. Phenotype cannot directly tell you what the individual’s genotype is because recessive genes will be masked by dominant ones
Most higher forms of animal life reproduce as the result of the mating of a male and a female. Remember: each parent is carrying two copies of every gene. However, during the formation of the female’s egg cell and the male’s sperm cells the two sets of genes divide in half, and then re-join in a new combination when the egg is fertilised and the embryo starts to develop. This results in the offspring having its own unique set of genetic material, inherited in exactly equal amounts from its two parents.
So, How do We Apply all this Theory to the Breeding of Suris?
The suri is another example of dominance, just like the brown eyed gene in humans. The suri fleece gene is dominant and the huacaya fleece gene is recessive. This means that in order to be a huacaya the alpaca is only carrying huacaya genes. They are “homozygous for the huacaya gene” and if you mate any two huacayas together you will always get a huacaya.
However, because the suri gene is dominant there will be some suris who are “homozygous” and have two suri genes and some who are “heterozygous” and have one suri gene and one huacaya gene. They will look basically the same – that is, they have the same “phenotype” (suri) even though the “genotype” is different.
Try thinking of these genes as pairs of playing cards, placed one on top of another. The card you can see on top indicates the “phenotype” – suri or huacaya – but it is important to know what the “hidden” card is!
What happens when we mate two suris? If both parent animals are homozygous (meaning they only have suri genes), then the offspring will, of course, also be homozygous suris.
If you mate one homozygous suri with one heterozygous suri, you will also always get a suri offspring, but half of them will be heterozygous, having a “hidden” huacaya gene!
If you mate two heterozygous suris, however, you have a 50% chance of producing a heterozygous suri, a 25% chance of producing a homozygous suri but also a one in four chance of actually producing a huacaya!
Many suri breeders will have cross-bred suris within their herd – that is, suris that have a huacaya ancestor somewhere in their background. Again, there are some special terms used to describe these animals:
- First Cross or F1: a suri produced by mating a huacaya to a suri (most commonly it is the dam who is the huacaya and the sire the suri)
- Back-Cross One or BC1: a suri produced by mating an F1 to a suri (again, the sire is likely to be the suri). Also referred to as a “Second Cross” or “second generation suri”
- Back-Cross Two or BC2: a suri produced by mating a BC1 to a suri. Also referred to as a “Third Cross” or “third generation suri”
- Back-Cross Three or BC3: a suri produced by mating a BC2 to a suri
It is considered by many breeders that by the 4th generation – that is, BC3 – a suri can be considered “pure”, having 93.75% suri blood and an 87.5% chance of being homozygous for the suri gene.
Although the fleece of most F1s will not display all the desired characteristics of suri fleece (in particular the lock structure will probably not be as well defined), with each generation of back-crossing the style will usually improve, provided that top-quality, homozygous suri males are used at all times.