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Dog Genetics 101

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Genetics is the study of how DNA is passed down from one generation to the next. It is a complicated, always-changing field. Here, we’ll explain the basic concepts in dog genetics and define some genetics terms that you might see in your dog’s Embark results.

Key terms in dog genetics explained

You may see some of these terms in your dog’s genetic results. For more genetics words and definitions, see the National Human Genome Research Institute glossary.

What is DNA?

DNA stands for deoxyribonucleic acid. It is a long, chain-like molecule that is present inside most cells.

DNA is made up of four letters (also called “bases”):

  • Adenine (A)
  • Thymine (T)
  • Cytosine (C)
  • Guanine (G)

These letters follow specific, predictable rules. A always pairs with T, and C always pairs with G.

What is a mutation?

A mutation, also called a variant, is a change in the DNA sequence. While we often associate mutations with adverse health conditions, most of them have no effect on phenotype. Many variants are neutral in their effect, some are associated with different traits, and some are associated with health risks.

What is a gene?

Scientists consider the gene to be the basic unit of inheritance. A gene is a section of DNA that codes for a specific trait or characteristic. Most genes code for proteins that do specific jobs in the body. Genes are passed down from parents to offspring in certain patterns, called modes of inheritance

What is an allele?

An allele is one variation of a DNA sequence for a specific gene or a particular location in the genome. You may also hear alleles referred to as “copies” of a gene. Dogs, humans, and most other organisms have two alleles for each location—one from each parent.

The genes that code for some traits and conditions have multiple alleles. For example, a dog could have one allele for a short coat or a different allele for a long coat.

What is a chromosome?

A chromosome is a long strand of DNA that lives in the nucleus of each cell in the body. In biology, a chromosome is often represented by an X shape.

Generally, an individual gets one full set of chromosomes from each parent. We count chromosomes in pairs. Humans have 23 pairs of chromosomes (46 total). Dogs have 39 pairs of chromosomes (78 total).

What is the genome?

The genome is the complete set of genetic material (DNA) in an organism.

What is a locus?

A locus is a specific location in the genome. The plural of locus is loci, meaning many locations.

What are modes of inheritance?

Modes of inheritance simply mean the way genes are expressed. At Embark, many of our health and trait tests refer to Mendelian, or simple, inheritance—also known as dominant and recessive traits. (However, genetics is a complex field, and there are many other ways genes are expressed!)

What does genotype mean?

Genotype refers to the specific DNA sequence for a particular locus. You’ll usually see this expressed as a pair of letters (for example, GG or GT). 

What does dominant mean?

A dominant allele is one that is expressed when paired with a recessive allele. This means that even if an individual has only one copy of the dominant allele, it will still be expressed.

For example, the gene FGF5 is known to affect hair length in a dog’s coat. Short coat length (G) is a dominant trait in dogs. Dogs who have either one copy (GT) or two copies (GG) of the short coat allele will have a shorter coat. 

What does recessive mean?

A recessive allele is one that is only expressed if an individual has two copies of it. If an individual has one copy of the recessive allele and one copy of the dominant allele, the dominant trait will be expressed. 

For example, long hair (T) is a recessive trait in dogs. A dog must have two copies of the long hair allele (TT) to show long hair in their coat.

What does phenotype mean?

Phenotype refers to the physical expression of an individual’s genotype, or their outward appearance. For example, a dog’s genotype for coat length might be GT, with a short coat phenotype. Another dog’s genotype might be GG, while they also have a short coat.

Looking at phenotype alone doesn’t reveal a dog’s genotype. That’s why a dog’s breed results can be so surprising.

What does homozygous mean?

Homozygous means an individual has two copies of the same allele (GG or TT).

What does heterozygous mean?

Heterozygous means an individual has two different alleles (GT).

What does it mean to be a carrier?

A dog who is a carrier has one copy of a gene (an allele) that is associated with a condition or trait where two copies are required for the condition to show. A carrier often does not show signs of the condition or trait, but they could pass that allele on to their offspring.

What does “at risk” mean?

If a dog has enough copies of an allele that is associated with a health condition, we say that the dog is “at risk” for that condition. “At risk” simply means a higher-than-average risk. It is not a guarantee that the dog will necessarily develop that condition. Learn more about what at-risk and carrier status mean.

What does “autosomal” mean?

When we talk about human and dog genetics, we usually refer to two types of chromosomes: autosomes (most chromosomes) and sex chromosomes (the X and Y chromosomes). 

In dogs, 38 of the chromosomes are autosomes, and one is a sex chromosome. Female dogs have two X chromosomes, while male dogs have one X chromosome and one Y chromosome.

What is a haplotype?

A haplotype is a generic term for a single copy of a dog’s genotype. (Haploid means one copy of each chromosome; diploid means two copies.) It refers to a physical grouping of genetic variants that are located on the same chromosome. Because these variants are physically linked to each other, they tend to be inherited together. You can think of a haplotype as a set of genes coming from one parent.

At Embark, we use certain haplotypes—namely, mitochondrial DNA (mtDNA) and Y chromosome haplotypes—to trace a dog’s maternal and paternal lineage.

What is epigenetics?

Epigenetics is a field of study related to genetics. It focuses on DNA modifications that do not affect the sequence of letters in DNA, but instead affect the proteins and chemical markers that interact with DNA. These chemical modifications can affect which genes are turned on and off. 

The collection of all epigenetic changes in a genome is called an epigenome.

What are complex diseases?

In genetics, a complex disease is one that is influenced by both genes and the environment. Because many factors are at play, a complex disease can’t be traced to one single gene or cause. 

Cancer is one example of a complex disease. There are many genes associated with cancer risk, but lifestyle is also an important factor that influences whether someone will develop cancer.

What does polygenic mean?

A polygenic trait is one that is influenced by more than one gene. Because multiple genes are involved, polygenic traits don’t follow the rules of simple Mendelian inheritance we discussed above. Coat color and eye color are two examples of polygenic traits. 

Frequently asked questions about dog genetics

These are some common questions our team receives about Embark results and about dog DNA in general.

What is the difference between genotype and phenotype?

An individual’s genotype is the combination of alleles they have for a gene—their specific sequences of DNA. Their phenotype is their physical appearance.

To illustrate this concept using coat length as an example, the different genotype and phenotype combinations for this trait would be:

If a dog has this genotype: They are: With this phenotype:
GG Homozygous Short coat
GT Heterozygous Short coat
TT Homozygous Long coat

Why doesn’t my dog’s breed ancestry match their appearance?

The answer to this question relies on the difference between genotype and phenotype. Dog breeds are defined by specific, recognizable physical and behavioral traits. A variety of different genotypes can cause the same physical traits. Learn more about breed surprises and why breed doesn’t always dictate appearance.

What is “Supermutt?”

Many dogs descend from other dogs that were themselves mixed breed. The further in the past your dog has purebred ancestors, the smaller the identical segments matching our reference dataset are. In such cases, the best matches to our reference dataset are so small that they can no longer be confidently assigned to any one particular breed. Instead, these are assigned to the “Supermutt” percentage.

What is a village dog?

Village dogs are free-ranging, free-breeding dogs whose ancestors were indigenous to a geographic area. In effect, they are the descendants of the founding population of dogs in a region. Although they are not recognized by kennel clubs as a breed, they are a distinct population of dogs.

Embark’s co-founders have studied village dogs on six continents since 2007 in their efforts to understand the history, traits, and health of the domestic dog. Learn more about village dogs with Dr. Adam Boyko.

Continuing dog genetics research

We hope this genetics 101 overview helped explain some of the complex concepts in genetics. Test your knowledge with our Intro to Genetics quiz. If you’re interested in more, you can keep reading about how dog DNA tests work in this in-depth article.

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We are always learning more about the dog genome and how dog DNA relates to health. By testing your dog with Embark, you can contribute to more discoveries that help us understand dogs better. Join us in our mission to improve canine health and longevity through the power of science and technology.

Mimi Padmabandu Contributor

Mimi Padmabandu is a scientific writer and Content Strategy Lead at Embark Veterinary. She has over a decade of experience writing about science and genomics for leading biotechnology companies. She holds a bachelor's degree in Molecular, Cell, and Developmental Biology from UCLA and a master’s degree in Early Modern English Literature from King’s College London.

Read more about Mimi Padmabandu

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