An introduction to canine genetics

The genetic programme in the nucleus of a cell is always the same, regardless of whether the cell is in the heart or the skin. Each cell translates a very small part of the entire genetic program.

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Genes: architects of life

The structure of the cell nucleus is split into long threads that form the chromosomes. The number of chromosomes in the cell nucleus is always the same in a given species. Dogs have 78, while humans have 46. Chromosomes come in pairs, so it is more correct to say that dogs have 38 pairs of chromosomes plus one pair of sex chromosomes (XY in males, XX in females). The chromosomes carry the hereditary traits. In each pair, one chromosome comes from the mother and one from the father.

Each chromosome is formed by a deoxyribonucleic acid (DNA) molecule coiled in the shape of a ball. When a DNA molecule is unpicked its highly specific double helix structure is revealed. A single molecule of DNA contains enough information to fill an encyclopaedia running to several thousand pages. If you were to place all the DNA molecules in the chromosomes of a cell in a row it would measure around three feet!

The chromosome can be compared to a hollow rod, divided into thousands of segments. Each of these segments – known as loci (s. locus) – is occupied by a specific gene.

A gene contains all the genetic information (code) a cell needs to synthesise a specific protein. Dogs have around 20,000 different genes (compared with 25,000 in humans).

© Diffomédia/Royal Canin

Genes: the memory of life

All the chromosomes are arranged in pairs, with the gene from the mother located opposite the gene from the father. There are generally several distinct forms of the same gene, which thus code for different versions of the same protein. These forms are known as alleles.

An allele is either dominant or recessive. Recessive traits cannot express themselves unless they are present on both chromosomes. In this case, the dog is a homozygote. The dog is a heterozygote if one of the genes is generally dominant over the other. In this case, only the traits of the dominant gene will be expressed. The different allele combinations thus produce heterogeneity within the species and give rise to the various breeds. In genetics, traits are generally represented by a letter.

The dominant trait is written with a capital and the recessive trait with a lower case letter.

© Diffomédia/Royal Canin
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