Genetics part I: A short introduction

by Annika Farstad
© 2006

We will begin our article series on genetics by looking at the very basics of genetics.


Genes, Chromosomes & Locus:
A gene is a submicroscopic particle that is the basic unit of heredity. The body has hundreds of genes that are attached to a long string, called a chromosome. Genes always occur in pairs. Every dog has 78 chromosomes, or, more correctly, 39 pairs, each carrying hundreds of genes. Whilst scientists are still trying to find out where all the genes fit on the chromosome they do know that the place is always the same. The name of the place that they sit is known as the locus (plural being loci).

Allels:
Each gene has variations that produce different characteristics; these variations are called alleles and are symbolised using a letter system. While every gene has at least two alleles, some have more than two. However, no matter how many alleles (variations) a gene may have, a dog will only ever inherit two, one from each parent.

Homozygous & Heterozygous:
The alleles of a pair can be the same (homozygous) or different (heterozygous).

Phenotype & Genotype:
The more dominant allele will be what you can see (phenotype). The other stays hidden and is carried as a recessive gene for the future (genotype).