What is DNA diagnostics?

What is DNA diagnostics?

Approximately 450 inherited diseases have been found in dogs and more diseases are diagnosed every year. Different kinds of DNA based tests are constantly developed to help the breeders to make decisions concerning breeding. By testing dogs, cat and other domestic animals many harmful gene defects can be avoided. Tests reliably separate normal, carriers and affected individuals from each other and that information can be used in breeding decisions.

Most traits are inherited in autosomal recessive fashion, but also some dominant and X-linked inheritance exists. The best benefits from the tests are gained when the patterns of inheritance, the effects of certain genes that influence on different phenotypes and the restrictions and problems of the tests are well understood.

Influences of the genes

Genes exist in the DNA strand which is packed in chromosomes. Dog has 76 chromosomes and two sex chromosomes (XX female, XY male) so it has 39 chromosome pairs. One of each chromosome of the chromosome pair is inherited from the dam and one from the sire. The Y chromosome is inherited from the sire so the sire determines the sex of the offspring.

Genes can have many different alleles in other words forms of the genes that differ at some extent from each other. A dog has two alleles of every given gene and they are so called gene pairs. When alleles of a given gene are copies of each other they are homozygous. If they differ from each other they are heterozygous. A trait can be polygenic or monogenic. A trait being monogenic only one gene contributes to a certain phenotypical characteristic and if a trait is polygenic many different genes contribute to a phenotype. A character is dominant if it manifests in the heterozygote and recessive if not. Heterozygote of a certain recessive disease allele is the carrier of that disease and can pass the defect to its offsprings. Most diseases tested in gene tests are in fact recessive.

Why is it important to offer DNA diagnostics for dogs?
Dogs carry more familial diseases than any other animals. This is an unwanted "byproduct" of intensive and selective breeding of dogs during the last two hundred years. Annotation of the canine genome allows modern DNA diagnostics to offer new tools to fight against inherited diseases. Gene tests offer the following advantages:

· Gene tests can be used to diagnose different diseases (e.g. certain eye diseases)

· Gene tests can be used to detect gene variants that are known to increase risks for certain diseases. The risk of getting these diseases can be estimated.

· With the help of genetic testing breeding decisions can be made so that diseases are eliminated from the breed.

· Gene tests help to keep healthy carriers of the disease in breeding. This is important in order to improve and keep genetic diversity in the breed.