Like E=MC Squared
by Doc Skinner
December, 2000
The Mendelian Theory mapped how characteristics are
transmitted from one generation to the next. If anyone thinks
this holds the answer to breeding superior animals, they believe
in fairy tales.
Mendel mapped out his theory by recording observable
characteristics that were not appreciably affected by the
environment. These characteristics were carried by just a few
genes whose dominant and recessive potentials responded in a
predictable manner.
The inheritance of coat color has been worked out because the
results are observable and could be documented and analyzed.
Although the results are not always predictable because of the
number of alleles involved, the possibilities can be predicted.
The large number of genes and alleles in the dog’s genome
makes it impossible to predict many of the characterisitics. Man
has 46 chromosomes in his body cells, dogs have 78. A chromosome
can be thought of as a rod with beads threaded on it, each bead
being a gene. Since one of each pair of chromosomes comes from
each parent, you could say the dog has 39 pairs of chromosomes.
Genes for particular characteristics are always found at the same
location or locus on the chromosome. If the genes were simply
dominant and recessive such as BB for black and bb from brown, it
would be easier to determine the outcome of a breeding. The genes
B and b are influenced by alleles on the same location that can
change or modify the color. An allele may be thought of as a
mutation that occurred probably due to a biochemical change in
the enzyme system. Melanin, a dark pigment, is produced by an
enzyme reaction on the amino acid taurine, modifications of this
can result in color changes. Here Darwin’s theory comes into
play. If the mutation is an advantage or not neccessarily a
disadvantage, it may be maintained through the benevolence of
Mother Nature.
It is safe to say, that the environment does not appreciably
affect the coat color and if it is, it is not transmitted
genetically since it is an acquired characteristic. Many of the
desired characteristics of a gun dog such as a big nose are
genetically unknown. We do not know how many alleles are involved
or how the environment might affect it. Breeding is often done
blindly with the hope that a certain family carries a sought
after characteristic.
Getting back to the rod like chromosome and the bead like gene,
don’t think of the rod as having to be straight; but more
like a pipe cleaner that has been bent into a definite shape that
is always reproduced. The chromosome consists of D.N.A. and
protein while the gene consists of only D.N.A. D.N.A. being
peculiar to the individual has made it useful in determining
identity. The gene’s D.N.A. becomes involved in biochemical
reactions that lead to a definite result, such as the production
of melanin. Yellow color can be produced by a second gene
oxidizing the effect of the black pigment gene resulting in
yellow instead of black. However, the black gene is still present
in the yellow dog and if bred to an individual carrying a black
gene, can produce black puppies.
To reiterate, a single gene with dominant and recessive
characteristics is simple Mendelian. If it involves multiple
allels, the alleles are arranged in their degree of influence.
The most influential being epistatic and the least influential
hypostatic. All the alleles above a particular allele are
epistatic to it and all the alleles below are hypostatic to it.
We mentioned that each individual has two members of an allelic
series, the exception being when the characteristic is sex
linked. Females have two X Chromosomes, they are XX. Males are XY
so they only have one X-chromosome. Therefore, whatever gene they
carry on their X chromosome will be expressed whether it is
dominant or recessive because it is the only member present. An
example being, all three colored cats are female. If a three
colored cat occurs, it is sterile because it’s genetic
makeup looks like XXY. Somewhat similar mistakes produce
hermaphrodites. Going back to Darwin’s survival of the
fittest, the change is a disadvantage and self-limiting due to
sterility. Some genes are modifiers, modifying the action of
another gene. Actually all genes affect their pair member to a
greater or lesser degree.
The inheritance of beagle characteristics depends on so many
genetic influences that the simple laws of Mendel are of no
assictance to the serious breeder. Breeders must also draw on a
limited number of results, which are probably statically
insignifigant.
Have fun breeding your beagles but don’t expect to corner
the market, it will only last so long. Knowledgeable culling is
probably the serious breeders most effective tool. As breeders,
the traditional brace people have done an amazing job of
constantly selecting recessive characteristics to produce hounds
of remarkably similar disablity. Domestication has produced many
changes that would not have survived the more stringent selection
of mother nature.