Breeding and records terms, explained

DNA reports and animal paperwork use a small set of terms again and again. Here’s what each one means, in plain words. Our guide on how to read a genetic test result puts the genetics terms together.

On a DNA report

Affected

An animal with enough copies of a variant to have the condition: two copies for a recessive condition, and one can be enough for a dominant one. Some labs say “at risk” instead.

Allele

One version of a gene. An animal has two alleles at each spot, one inherited from each parent.

Carrier

An animal with one copy of the variant for a recessive condition. It is usually healthy itself, and passes the variant to about half of its offspring.

Clear

Also called normal. The animal doesn’t have the variant the lab tested for. It says nothing about other variants, including other forms of a condition with a similar name.

Dominant

A condition where one copy of the variant is enough to cause it. HYPP in Quarter Horses is inherited this way.

Genotype

The pair of alleles an animal has at one spot, written with a slash, such as N/N or N/HRD.

Heterozygous and homozygous

Heterozygous means the two copies differ, as in N/HRD. Homozygous means they’re the same, as in N/N or HRD/HRD.

Mode of inheritance

How a condition passes from parents to offspring, such as dominant or recessive. A lab’s page for each test usually states it.

Panel

A set of tests run together, such as a breed’s disease panel.

Recessive

A condition that needs two copies of the variant. Breeding two carriers gives, on average, one affected offspring in four. HERDA in Quarter Horses is inherited this way.

Variant

The specific change in the DNA that a test looks for, sometimes called a mutation.

For breeding decisions

Coefficient of inbreeding (COI)

The probability that the two copies of a gene at a given spot came from the same ancestor through both parents. A higher COI raises the chance of recessive problems. Our guide explains how it’s worked out.

Parentage verification

A DNA test that checks whether the recorded sire and dam are really the parents, by comparing the offspring’s DNA markers with theirs. Our guide explains how it works.

Pedigree

The record of an animal’s ancestors. A COI worked out from a pedigree can only count the ancestors that are recorded, so a short pedigree makes it look lower than it is.

On animal paperwork

Certificate of Veterinary Inspection (CVI)

A health certificate from a licensed veterinarian, usually needed to move an animal between US states. For horses, most states want it written within 30 days of travel.

Coggins test

The blood test for equine infectious anemia (EIA). Every US state requires a negative one before a horse crosses state lines.

Health clearance

The result of a health screening, such as a hip or elbow evaluation, an eye exam, or a cardiac check, with the date and who carried it out.

Registration and transfer

Registration is an animal’s entry in a breed registry’s official record. A transfer is the registry’s record of a change of owner.

Sources

• UC Davis Veterinary Genetics Laboratory, HERDA and HYPP
• US Equestrian, Interstate travel