Introduction to Australian Rat Genetics

Australia has a limited set of genes with which to work when compared with the variety of genes overseas. The majority of genes within the Australian rat fancy are Mendelian in nature. They are explained on the Genes page in more detail.

Mendelian Genetics was derived from the work of the Augustine monk Gregor Mendel, who conducted experiments creating hybrids in plants in the 1860’s. Mendel discovered that genes, also referred to as traits, normally occur in pairs. Each member of a pair is called an allele.

An animal inherits one set of alleles from its mother, and another set of alleles from its father. The alleles from both parents make up pairs, and it is these pairs that determine what the animal will look like, also called its Phenotype.

Mendel also discovered that each allele could be either recessive or dominant in nature and that the dominant allele of a pair had a different effect on the appearance/phenotype of an animal than the recessive allele.

When an animal inherits two alleles from its parents that contain the same information (ie, are both recessive alleles or both dominant alleles), the animal is said to ‘Homozygous’ for the gene/trait. When an animal inherits two alleles from its parents that contain different information (ie, one is a recessive allele and one is a dominant allele), the animal is said to be heterozygous for the gene/trait.

A dominant allele, represented by a capital letter, will always be visually expressed. A recessive allele requires BOTH of the alleles within the pair to be recessive for it to be visually expressed.

In written form, dominant alleles are represented as a captital letter, eg, ‘A’ and recessive alleles by a lower case letter, eg, ‘a’.

Example

Bug the pet rat drinking out of a water bottle
A non-agouti rat, with the alleles ‘aa’
Grub the pet rat peeking out of a tube
An Agouti rat, with the alleles ‘Aa’ or ‘AA’

‘A’ represents Agouti and ‘a’ represents Non-Agouti.

If a rat inherits an ‘A’ allele from one parent and another ‘A’ allele from the other parent, making the pair of alleles ‘AA’, this is visually expressed by the rat being Agouti.

If a rat inherits an ‘A’ allele from one parent and an ‘a’ allele from the other parent, making the pair ‘Aa’, this is visually expressed by the rat being Agouti. This is because one of the allele is dominant over the other one (represented by the capital letter) , and as ‘A’ represents Agouti and is the dominant allele of the pair, the rat will be Agouti. The other allele of the pair, ‘a’ which represents non-agouti, will be hidden by the dominant gene. This means that as the dominant allele has made the rat Agouti, there is no way to visually tell that the rat carries the recessive ‘a’ non-agouti allele.

If a rat inherits an ‘a’ allele from one parent and another ‘a’ allele from the other parent, making the pair ‘aa’, this is visually expressed by the rat being non-agouti. This is because BOTH of the alleles in the pair are recessive.