Recessive Traits in Guinea Pigs

Due to our recent Facebook post on genetic conditions in certain types of guinea pigs, I thought we could take a more in depth look at genetic inheritance and recessive traits.

For many traits, like coat colour, coat length or type, eye colour and genetically inherited disease conditions, there are 2 or more versions that could be expressed in any individual. Taking the example of coat length, a guinea pig may have long fur, or short fur. These versions of a particular gene are called alleles. They differ from each other by having slightly different base sequences in their DNA, resulting in a different expression of the characteristic.

For these characteristics one allele (or version of the DNA) is inherited from the mother and one allele is inherited from the father. So, every individual will possess two alleles for each of these genetic traits. The two alleles could be the same or different. Which one of the alleles is expressed (if they are different) depends on which one is dominant and which one is recessive. The dominant allele will always be expressed over the recessive one. So, in order to express the recessive trait, the individual must inherit the recessive allele from both parents.

If an individual has 2 of the same alleles for a genetic trait, they are termed homozygous. If they have 2 different alleles, they are termed heterozygous. The alleles that are inherited are called the genotype of the individual. The expression of the alleles (the coat length for example) is called the phenotype.

Genetic conditions in Guinea Pigs: In the case of recessive genetically inherited conditions both parents, of an affected individual, must have at least one recessive (disease) allele. If the parent has 2 recessive alleles, they will themselves also have the condition. If the parent has only 1 recessive allele, and therefore 1 dominant allele, they will not have the condition but will be a carrier of it (i.e. they have the ability to pass the disease on to their offspring if mated with another carrier or affected individual).

• Examples of recessive, genetically inherited conditions in guinea pigs include Satin Syndrome and Lethal White Syndrome.

This can perhaps be more easily understood in diagram form. Firstly, taking the example of coat length. Short fur is dominant over long fur. We will represent the dominant allele for short fur by 'B' and the recessive allele for long fur by 'b'. So, a short-furred individual may have the genotype BB or Bb. However, a long-furred individual will always have the genotype bb. The diagram below shows the potential coat length of offspring from mating a short haired guinea pig with a long-haired guinea pig.

Inheritance of coat length in guinea pigs

In the case of a genetically recessive inherited condition, we could represent the allele for the disease-free state with D and the allele for diseased state with d. It is likely we would only mate parents who do not express the disease. However, if they are both carriers of the disease (i.e. their genotypes are both Dd) their offspring will have a 1 in 4 chance of having the disease (genotype dd), a 1 in 4 chance of being disease free and not being a carrier (genotype DD) and a 1 in 2 chance of being disease free but being carriers (genotype Dd). See the table below:

Recessive disease inheritance in guinea pigs

In conclusion, a recessive trait or a recessive genetically inherited disease will always be expressed in the minority of the population. Recessive inherited diseases will only occur in 25% of the offspring from mating 2 individuals who both possess at least 1 recessive allele (i.e. are carriers of a disease) and will not occur at all if one parent is homozygous for the dominant allele. An understanding of genetics is important for anyone breeding guinea pigs as recessive diseases can be eliminated by not breeding two carriers together.