Different mutations have different modes of inheritance, depending on how many affected alleles need to be present in an animal to cause the clinical features linked to that mutation. Explanations of the different modes of inheritance are given below. In these examples, ‘wt’ represents the normal (wild-type) allele, and ‘mut’ represents the affected, mutant allele.
Autosomal Mutations
Most of the tested mutations in our catalogue are autosomal: they are located on an animal’s “standard” chromosomes, instead of its sex chromosomes, mitochondrial DNA, etc.
Autosomal Recessive
A recessive mutation needs to be present on both alleles to cause its phenotype. Only affected animals (mut/mut) will present with the described clinical features.
Autosomal Dominant
A dominant mutation only needs to be present on one allele to cause its phenotype. Carriers (wt/mut) and affected animals (mut/mut) will both present with the described features.
Autosomal Semi-Dominant
A semi-dominant mutation can combine with the wild-type to create a different phenotype for carriers. An animal with a wt/mut genotype will develop the phenotype for carriers, and an animal with mut/mut will develop the phenotype for affected animals.
Autosomal Co-Dominant
A co-dominant mutation can combine with the wild-type to create a less intense version of its normal phenotype. An animal with a mut/mut genotype will develop the described clinical features, and an animal with a wt/mut genotype will develop a lesser version of those features.
X-Linked Mutation
In mammals, the X-chromosome is involved in the determination of sex. Females have two X-chromosomes (X/X), while males have one X-chromosome and one Y-chromosome (X/Y). If a particular allele is on the X-chromosome, that means that a male will only have one allele, instead of the usual two. If a male carries an X-linked mutation, it is automatically considered affected by that mutation.
X-Linked Recessive
In females, an X-linked recessive mutation behaves the same as an autosomal recessive mutation: only affected animals (mut/mut) will present with the described clinical features. Males only need one mutated allele (mut) to develop the features.
X-Linked Semi-Dominant
In an X-linked semi-dominant mutation, affected females (mut/mut) and affected males (mut) will develop the described clinical features for affected animals. Carrier females (wt/mut) will develop the described clinical features for carriers instead.
Mitochondrial
A mitochondrial mutation is located on an animal’s mitochondrial DNA, which is separate from its chromosomal DNA. An animal carrying a mitochondrial mutation (mut) is automatically considered affected by it. An affected female will pass the mutation to all her offspring. Males do not pass down mitochondrial mutations.
Incomplete Penetrance
Some mutations in our catalogue are described as incompletely penetrant (e.g. incompletely dominant, incompletely recessive). This means that it will often, but not always, cause the described clinical features.
Risk Factors
Some mutations are described as risk factors. An animal that tests as positive (either wt/mut or mut/mut) for a risk factor has an increased risk of developing the described clinical features, but is not guaranteed to.
Multifactorial Inheritance
If a trait is multifactorial, that means that it is dependent on several different genes, as well as possible environmental factors such as diet and living conditions. A mutation with multifactorial inheritance can influence the animal towards a particular phenotype, but does not necessarily guarantee it.
