There
was an outcry within the Azawakh community
during the summer of 2002. Some of the
committee members of the French SLAG had
suggested improving the breed by selectively
cross breeding the Azawakh with the Sloughi.
The genetic pool of Azawakh was said to
be too small in Europe. Are those worries
founded? What are the reasons? And what
is there to be done (if at all necessary)?
Before I deal with the questions above,
let me first explain, as simply as possible,
some of the very basics of biogenetics.
The
cell - the foundation material
The
cell consists of cell body and cell nucleus.
The latter is a carrier of genetic information
material. It contains kernel threads or
chromosomes, which always exist in pairs.
The dog has 78 chromosomes, therefore
39 chromosome pairs.
The
hereditary material is divided into units.
They are called microsatellites and are
genetic mark stones. The dog possesses
50.000 of those microsatellites. Each
microsatellite has its own special place
on the chromosome and this varies from
dog to dog. The closer two dogs are related
to one another the more similar will their
microsatellites be.
Picture: Homozygous allele pair - Heterozygous
allele pair
Genes
- the carrier of genetic information
The
smallest units of genetic information
are genes. Chromosomes do not exist individually,
they are always made up of pairs - homozygous-
each gene belonging to another partner-gene
or homozygous gene (allele).
We
assume that dogs have more than 100.000
allele pairs, and therefore 200.000 genes.
The section where two alleles are located
on one chromosome is called gene location
(gene locus). A specific gene can always
be found in the same location on a chromosome.
And this specific gene will always influence
one specific characteristic/trait and
only ever this one. One chromosome from
a chromosome pair stems from the father
and the other from the mother. The male
and the female dog contribute each half
of the genes.
One
allele can suppress another one, which
affects the hereditary result. If such
an allele occupies a mixed hereditary
gene location, the weaker allele will
be suppressed and the stronger, more dominant
gene determines the phenotype. Those genes,
which cannot push through are called recessive
genes.
Recessive traits/characteristics can only
be seen in the descendants of mixed hereditary
dogs, if their carrier in one animal is
pure hereditary. This means that those
genes are located in pairs at the same
gene location. This fact plays a vital
role when we look at hereditary defects,
as quite a number of those are inherited
recessively. If an allele pair contains
the same genetic information the dog is
considered for this specific trait homozygous.
Should the alleles for this characteristic
be different, the dog is then considered
for this trait heterozygous. The genetic
make-up of a dog is in parts pure hereditary
(homozygous) and in other parts mixed
hereditary (heterozygous). Dogs where
all traits and characteristics are homozygous
do not exist.
In
accordance with genetics
When
we look at the effects of hereditary factors,
we can differentiate between the following
possibilities:
1.)
One gene influences one trait.
2.) One gene influences more than one
trait.
3.) A number of genes influence the shaping
of a trait, in this case we speak of a
polygenetic hereditary make-up, polygenetic
or multifactor genetics.
Usually
not only one specific gene is responsible
for certain traits or characteristics,
but it is the combination of a number
of different genes. Such a polygenetic
hereditary make-up is the basis of nearly
all quantitative traits and characteristics.
The later could be the height, weight
and the degree of back legs, performance
- and natural characteristics. Qualitative
characteristics are fur and fur color.
Additive
genes can only be determined in appearance
if they fulfill a certain minimum number
(threshold). Such threshold effects can
also be seen when dealing with hereditary
defects. Some defects are changes (mutations)
of healthy genes, which were passed on
recessively. Often they stay hidden for
generations. Matching two mutations will
bring this phenomenon to light.
Table:
Heredity degree of different characteristics
in percentages
(taken from Hansen, Vererbung am Hund,
2001)
Characteristics
|
Heritability
in %
|
Heritability
|
Reproduction |
|
|
Fertility |
10-15
% |
low |
Size
of Litter |
10-20
% |
low |
Quality
of Semen |
15
% |
low |
Anatomy |
|
|
Anatomical
characteristics |
30-65
% |
medium
to high |
Shoulder
Height |
40-65
% |
high |
Length
of Body |
40
% |
medium |
Depth
of Chest |
50
% |
high |
Length
of Fang |
50
% |
high |
Behavior |
|
|
Hunting
disposition |
10-30
% |
low
to medium |
Temperament |
30-50
% |
medium
to high |
Nervousness |
50
% |
high |
Fear |
45-60
% |
high |
Sensitivity
to Shooting |
60-70
% |
very
high |
Disposition
for Tracking |
46
% |
high |
Ability
to Scent |
39
% |
medium |
Guarding |
10
% |
low |
Combined
Behavior Characteristics |
27-44
% |
medium |
The
heredity is the influence of the phenotype
through the genetic type. This can vary
between 0 - 100%. Hardly any characteristic
is hereditary 100% (please also compare
Claude Gaillard, Der Zuchtwart, in: Rassehund,
December 2002).
Selective
breeding is the way to enhance or suppress
traits and characteristics. The seemingly
easy rule in breeding tells us that only
those individuals should be bred with,
which combine the favorable traits and
characteristics in a breed and which come
as close as possible to fulfilling the
breeds standards. Of course there will
always be questions on how sensible a
breed standard really is and who should
determine a breed development.
Usually
breeders have a vast pool of non-related
breeding individuals to choose from. This
is especially important when genetic mistakes
show within a homozygous selection and
therefore need to be corrected. These
possibilities can only be applied to the
Azawakh breed, due to its fewer and more
limited numbers, to a certain extent.
Selection always means genetic changes
and losses. Selective and repeated selection
changes the frequency of occurrence of
specific genes within the whole breeding
population.
When
deciding upon genetic losses one has to
look closely at the breeding animal and
also seek help through inbreeding coefficients
and ancestral loss coefficients. The inbreeding
coefficient determines by which percentage
the heterozygous has decreased and the
homozygous has increased within a dog
comparable to the breeding average. The
formula of calculation by weight of the
inbreeding coefficients (IK) reads as
follows: IK=(1/2)n1+n2+1.
The
ancestral loss coefficients (AVK) (formula
designed by Prof. Schlegel, University
of Vienna) are the quotient out of a number
of uniquely found ancestors within the
overall group of ancestors.
Example:
Within a group of the third still know
generation are only eight out of 14 ancestors
different individuals, then the quotient
for this group will be 8:14=0,55. This
means an ancestral loss of 55 percent
.An AVK of 60 for example means a loss
of heterozygous of 40%.
Going
back to the question from the beginning
" The genetic impoverishment of the
Azawakh breed?" I have analyzed the
European stock (about 900 individuals
between 1999 to 2001) with taking the
IK and AVK into account. In order to gain
an annual average figure, all documented
individuals were given their IK and AVK.
These figures were then added and divided
by the figure of entries.
The
result shows a steady decline of the AVK
figure for the Azawakh population in France.
Towards the end of the 1990's the AVK
has sunk under the genetic threshold of
70 percent. In accordance to this development
the inbreeding coefficient increased over
its critical figure of 20 percent. There
is the serious development of the so called
"bottle neck effect" to be witnessed
where we went from the initial wide genetic
range of the Azawakh imports out of colonial
Africa to a situation which is not correctable
by the dramatic narrowing of the genetic
material of the current French breeding.
Graphic
3: IK - and AVK distribution on the example
of the French breeding
Graphic4:
IK - and AVK distribution on the example
of German breeding
The
German breeding started in the 1970's
in quite a similar situation in which
the French population is currently. Due
to the incorporation of Azawakh's from
France and imports from Africa, the German
breeding seems to be much safer and increasing
since the 1990's. Obviously there can
be a discrepancy of this statistical average
between different breeders and bloodlines
(please see graphic 6 - 8).
Homozygous
is considered within normal breeding activity
of pets as the key to optimizing a breed.
Inbreeding means to make dogs and their
genetic material homozygous. The bigger
the IK, the bigger the possibility that
descendants will be homozygous in certain
genes. There is obviously an open question
on which genes will be homozygous by such
breeding - the favorable ones or also
the unfavorable genes. To act like this
within a breed which is already few in
numbers and genetically limited could
have serious consequences, namely the
collapse of the breed as a whole. Recessive
genes in mostly polygenetic heredity often
determine genetic errors. The most undesired
characteristics or traits, which occur
within a homozygous bloodline, are hereditary
mistakes. Only descendants of breeding
individuals, who carry the recessive hereditary
genetically faulty homozygous material,
show this in their phenotype. That is
the reason why a characteristic, which,
through inbreeding, should have been strengthened,
is coupled with a faulty characteristic,
which is undesirable. Or it is the other
way around- the genes which are non -
desirable and which one wishes to eliminate
through inbreeding are coupled with a
gene which is most desirable. In a small
kennel the advantages and disadvantages
come very quickly to light.
By
rebuilding a new breeding population,
inbreeding can very quickly manifest itself
(often arbitrarily) in breed characteristics
defined by breeders and the kennel clubs.
If further inbreeding takes place more
disadvantages will show, this can be described
with the term of inbreeding depression.
Characteristics
|
Consequences
|
Vitality
|
lower
|
Longevity
|
reduction
|
Imunity
|
lower
|
Working
abilities
|
lower
|
Fertility
|
lower
|
Prolificity
|
reduction
|
Quantity
and quality of semence
|
lower
|
Stillborn
|
higher
|
Puppy
Mortality
|
higher
|
Growth
|
lower
|
Abnomalites
|
higher
|
Illness
|
higher
|
Environmental
Sensitivity
|
higher
|
Negative
results with inbreeding do not occur overnight,
nor do they show in a multitude or all
at the same time. Some bloodlines seem
to have a higher level of inbreeding tolerance
than others, before negative effects do
show. Even in very tight bloodline breeding
with relatively high IK and AVK, genetic
mistakes can stay hidden over a long period
of time. They can, through genetic luck,
stay within certain limitations or only
show certain physical or psychological
characteristics, which are not that obvious
to breeder or owner alike, or are simply
tolerated. This could have quite dramatic
effects as those negative results on the
phenotype und behavior could influence
both judges and the public luring them
into a sense of belief that those characteristics
are natural and on the whole desirable.
Partly through that, the broadness of
the "breeding philosophy" is
astonishing high. As an example we could
look at the IK - and AVK statistics of
litters of three Azawakh breeders. Tight
or inbreeding does not necessarily lead
to the end of the pole, especially if
IK and AVK get back in balance through
timely outcrossing. The threshold for
IK stands at the mark of ten and the AVK
threshold is believed to be at a figure
of 75. Tight - and inbreeding means, in
any case, unrecoverable genetic losses
and the risk of undesirable and illness
causing changes.
Graphic
6: IK- and AVK distribution at the example
of an inbreeding kennel
Graphic 7: IK- and AVK distribution at
the example of outcrossing
Graphic
8: IK- and AVK distribution at the example
of a bloodline kennel