The search for genetic markers affecting wool characteristics
Theopoline Omagano Itenge-Mweza
Wool production is a major agricultural industry world-wide, the most
important wool-growing countries include Australia, New Zealand, China, South
Africa and countries within South America. In New Zealand for example, the
industry generates NZ$1.3 billion in export revenue every year. And in
Australia, exports are valued at AU$3.4 billion annually.
Challenges
The wool industry is faced with many challenges that require innovative
solutions. The major competitors to the wool industry, cotton and synthetics,
have developed new fibres that meet consumer needs such as being lightweight,
soft and easy to care. These competitors have also made better productivity
gains than wool, which has resulted in lower prices for all textile products.
Today, there is much instability in wool prices, with a major problem facing the
industry in faulty wool production.
The wool characteristics that are of economic importance include fibre
diameter (or fineness), colour, grease and clean fleece weight, fleece length,
strength and bulk. For Merino and halfbred wools, fibre diameter is the major
factor that contributes to price variation as it significantly influences both
fibre processing properties and ultimate product quality. The colour of wool is
also important because superior colour (bright and white) can be dyed to the
maximum range of shades and consequently is worth more than poorer coloured
wool. Furthermore, the quantity of wool is important in overall wool production
and in the efficiency of the production system.
No simple solution yet
Wool characteristics, like many production traits, do not exhibit simple
Mendelian inheritance patterns (recessive or dominant). Instead, they are
complex and show continuous variation in phenotype (that is their appearance).
This suggests that wool characteristics are not only due to multiple genes, but
also environmental and management factors. Selective breeding has been practised
since the domestication of sheep in order to improve the quality and
marketability of wool. This has resulted in many breeds that are commercially
important today. The domestic sheep Ovis aries today comprises over 500
different domestic breeds. Selection of breeding animals was traditionally based
on the phenotype of the individual animal, a rather slow method of selection.
Other strategies to control environmental factors such as nutrition, time of
shearing or mineral supplementation tend to be costly.
The answer to sidestepping these drawbacks of cost and time may lie in
identifying specific genetic markers. Some sheep consistently produce quality or
faulty wool, suggesting that genetic factors are an important key in determining
wool characteristics.
What is a genetic marker - a quick tour
A gene is a segment of DNA that provides the genetic information necessary to
produce a protein. For almost all of the genes, there are two copies (alleles),
one inherited from the mother and the other from the father. In any population
of animals, there can be many different alleles. This is termed polymorphism or
genetic variation. Polymorphism results from DNA mutation. It is this
polymorphism that molecular scientists take advantage of in order to identify
genetic markers.
A genetic marker for a particular characteristic can be defined as a piece of
DNA that directly affects a phenotype and shows polymorphism. It can also be a
piece of DNA that is closely linked to another piece of DNA that affects a
phenotype. Genetic markers can either be genes or non-functional DNA segments
such as microsatellites or minisatellites.
Genetic variation of wool fibre
 An international team have gone in search of the genetic markers responsible
for wool quality. The team have targeted the keratin gene.
Wool fibre is mainly made up of the protein keratin which consists of two large
heterogeneous groups: the keratin intermediate filament proteins (KRT) and the
keratin IF-associated proteins (KAP). Each type of keratin protein is produced
from a gene and these genes have been reported to be polymorphic. However,
little research has been undertaken in this area.
They believe that polymorphism at the keratin gene loci is responsible for
the observed variation in wool characteristics and impacts on wool quality. If
their hunch is correct, then the potential of using this genetic variation in
marker-assisted selection for superior wool will be investigated and the
technology transferred to the industry.
A gel photo above shows polymorphism in one of the keratin genes, KAP3.2. Three alleles (A, B, C) for KAP3.2 are observed within ten different sheep
populations. Each lane represents a different sheep sample. The aim is to find
out if for example animals which inherited allele A have better wool quality
than those which inherited allele C.
Genetic markers versus genetic engineering
The search for genetic markers affecting wool quality traits is very
different to genetic engineering (GE). While the latter involves the
manipulation or modification of genetic composition of an organism, the former
detects changes within the genetic make-up of an organism, but does not alter
it.
The debate on GE will most likely continue and intensify especially where
animals are involved. However, marker-assisted technology in livestock offers a
powerful "green" alternative to gene manipulation.
Advantages
Genetic markers are not affected by environmental noise and provide a more
accurate and reliable way to assess the true genetic merit of sheep.
The identification of genetic markers would allow sheep breeders to select
animals with improved wool characteristics at an early age and cull the
non-desirable lambs. This would speed up the process of genetic selection and
decrease the generation interval. There is therefore a potential to select
superior animals very early in life and not have to wait for an animal to reach
its adult life to demonstrate that it has superior wool quality. This would mean
a more efficient and profitable wool industry with direct benefits of cost to
the consumer.
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