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Genetics

Introduction

These articles will provide a quick introduction to genetics. The story is focused on (breeding) dogs and especially the Border Collie. For a description of various terms I have provided a glossary of terms.

DNA

DNA helix structureEach cell of the body contains a copy of all the genetic properties. This information is stored in a very large molecule of a chemical compound. The compound is called DeoxyriboNucleicAcid or DNA for short. For a start it's enough to picture it as a double chain of beads, where the beads of the two chain are also interconnected. The entire structure has the shape of a double helix.
 

Chromosomes

Under the microscope masses of DNA can be made visible during cell division under certain conditions. These masses are called chromosomes. If you look well you can see that these chromosomes come in pairs. So there are two copies of the DNA.

An exception to this rule are the sex chromosomes. Females have two similar chromosomes; represented by XX and males have two different chromosomes; represented by XY. A few properties are located on the X-chromosome, which can cause nice effects (see also gender related properties).

The X- and Y-chromosome are also called sex chromosomes; the other chromosomes are referred to as autosomes. Everything that has to do with the 'other' chromosomes is often called autosomal.

Genes, loci and alleles

These concepts are often mixed up and used as synonyms. In itself not a crime, but for the sake of good order a clear and strict description will follow.
Locus
Is the name for an area on the DNA that codes for a certain property. The meaning of the word itself explains a lot: locus is Latin for location.
Allele
An allele is the possible content of a locus. An example: for the locus "Black" which determines whether the coat colour is black or brown, two alleles are known: B (black) or b (brown).
Gene
Often used instead of locus, but also instead of allele. Quite confusing, but often the meaning is explained by the context.
Since the DNA is present in duplicate every locus can fit two alleles (except for the properties on the X-chromosome, which has no duplicate in males!).

Cross diagram

To 'calculate' the results of a cross a diagram is often used. Horizontally and vertically the possible properties of the dog and the bitch are laid out and within the diagram you'll see the resulting combinations.
A a
A AA Aa
a aA aa
In the beginning this is a nice idea, but for crossings with four properties in a diagram you'll end up with 256 cells, which is quite confusing.


Copyright © 1998-2013 Jigal van Hemert & Danielle Boshouwers
URL: http://www.bordercollies.nl/egenintr.shtml
This page last modified: Wednesday, 30-Jul-2008 16:42:20 CEST
 
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