Why Doesn’t a Black Dog Always Have Black Pups? Coat Colour Genetics in Dogs 

Do you all remember colour theory from school? Red and blue make purple. Red and yellow make orange. Blue and yellow make green. Sounds sensible. So why is it that black Labradors can sometimes have puppies that are yellow or brown? As you may have guessed, genetics are involved and they are much more complicated than mixing paint. So today we will get into the details of how dogs get their coat colours.  

Overview Of How Genes Work  

As always, a little understanding of the science is necessary before we explain coat colour.  

The building blocks of life are deoxyribonucleic acid, or DNA. DNA strands are long chains of chemicals called nucleotides, forming the characteristic double-helix shape. Groups of nucleotides form genes. Genes are codes that can be translated into different kinds of protein. This is an incredibly complex process we will not detail today, but involves the DNA temporarily splitting to allow a copy of the code to be formed as messenger ribonucleic acid (mRNA). Specific amino acids (the chemical that makes up proteins) are then matched with the mRNA. The chain of amino acids then separates from the mRNA as a protein strand. This can be added to other protein strands to form the complete protein. Proteins are essential for body functions.

To use an analogy, if you want to build a house, you need to copy the instructions from a reference book (DNA) onto paper (mRNA). The instructions can then be used to build the frame (protein strands) which are combined to make the complete house (a whole protein).

Dogs have around 19,000 genes, humans have around 20-25,000 

Each gene is located on a specific point of a chromosome (a bundle of DNA). All chromosomes and most genes are paired. During reproduction, an offspring receives one random gene from each parent to create a pair. Genes can have minor changes in their code, called alleles. If a gene pair’s alleles are the same, they are homozygous, if they differ, they are heterozygous. Some genes are dominant, meaning they will always be available to produce proteins, whereas some are recessive and can only be used if its paired gene is also recessive.  

Not all genes are active and allow proteins to be produced all the time. Varying molecules, themselves proteins, regulate gene activation and turn off or on certain genes depending on the conditions. This is gene expression. When DNA replicates when new cells are created, every replication can lead to mistakes in the genetic code, called mutations. These mutations can have no effect, be harmful to the organism, or even lead to new traits.  

The specific combination of genes that make up an animal’s genetic code is termed the genotype. How this is expressed physically in traits like hair or skin colour is the phenotype.  

How Does Hair and Fur Gets Its Colour? 

Hair (and fur, because it is the same thing) gets its colour from melanin pigment produced by specialised cells called melanocytes. As the hair grows from the hair follicle, melanocytes migrate onto the hair. There are two kinds of melanin that affect hair colour – eumelanin (black/brown pigment) and phaeomelanin (red/yellow pigment). Eumelanin also affects eye and nose colour. Different kinds and combinations of melanin give different shades of hair which result in the huge variation in hair and fur colours in humans, dogs and other animals. Some hair can also have no melanin, resulting in white hair.  

In dogs, there are at least 15 genes with multiple alleles that regulate a dog’s final coat colour 

Proteins produced can also have variants, termed isoforms. We won’t get into specific details on every gene, but here are some simplified examples to explain how genes affect colour.  

• The MC1R gene codes for the MC1R protein that alters the timing and distribution of eumelanin; if it is switched off, no eumelanin is produced. However, the MC1R gene has seven alleles, not just “on” or “off”! 

• The ASIP gene codes for the ASIP protein that prevents MC1R protein activation (inhibiting eumelanin production) and promotes phaeomelanin production, resulting in more yellow hair.  

• Finally, the CBD103 gene codes for a protein that displaces ASIP protein, promoting eumelanin production again, causing black coat colour. This gene has three alleles.  

• Other genes are responsible for the distribution of the pigment, across the dog’s skin (leading to patches of colour, white spots, stripes, face colours), or within the hair (dilution genes leading to rarer colours like silver). 

With so many genes, alleles and protein isoforms, the haircoat of dogs is highly variable. Likely due to selecting for desired coat colours, through artificial selection, humans have increased the diversity of genetic mutations within dogs that lead to these varying coats.  Modern breed standards requiring certain coat colours have then resulted in relatively small populations with low genetic variation within certain breeds (for example, the majority of Labradors are entirely black, yellow or brown).  

There are also environmental factors that affect hair colour, such as UV-radiation from the sun (sun bleaching), pollution, dirt and other chemicals, and disease.   

Why Do Puppies Sometimes Look Different from their Parents? 

If this article has been complicated so far, unfortunately it doesn’t get any easier when it comes to puppies! 

As we have already discussed, every dog will receive half their genes from the mother and half from the father. Each puppy will receive a random selection of genes, with each having a different selection (aside from the extremely rare cases of canine identical twins). This includes the genotype that results in the dog’s haircoat phenotype. Remember that every gene is paired, and can be either dominant or recessive.  

Let’s take the hypothetical gene ‘A/a’ – the dominant gene is ‘A’ and the recessive ‘a’. Let’s say ‘A’ produces black fur, and ‘a’ yellow fur. A dog can only have yellow fur if both copies of the gene are ‘a’ (because the presence of the dominant ‘A’ would override the recessive ‘a’ and cause black fur). When a male and female dog mates, the offspring receives a copy of the ‘A/a’ gene from each. The combination results in the coat colour. This is best demonstrated using Punnett squares. Let’s assume each match results in four puppies. 

In this example, both parents have A/A genes (black fur), thus every combination of genes in the puppies is A/A (black): 

Here, one parent has A/a gene (black fur but carrying the recessive gene for yellow) and one A/A, resulting in all puppies having black fur, but two carrying the yellow gene: 

Here, both parents are carriers of the yellow gene (A/a), resulting in one puppy carrying both genes and being yellow, despite the parents being black: 

And finally, in an example where one parent is yellow (a/a) and one a black carrier (A/a), all puppies carry the yellow gene, and two present as yellow-coated: 

This highly simplistic example demonstrates how despite both parents having one colour, a puppy can have a completely different colour, thanks to recessive genes. Now combine this with multiple other genes and protein isoforms, and you can see how variation can occur. However, again because of tight breed standards, unexpected variation is generally quite low, and actively discouraged by many kennel clubs and breed associations. This means that when a dog’s genetics are known, puppy colour can be somewhat predictable.  

Does Coat Colour Matter? 

For scientists, dog breeders and kennel clubs, the genetics of hair colour might be interesting or useful, but should owners worry about a dog’s coat beyond personal choice? In fact, a dog’s colour may affect them more than you might expect.  

Genes can have multiple functions, and it has been shown that many of the genes involved in hair colour are also linked to the development of cells in the nervous, endocrine and skeletal systems. This means that activation of certain genes, often recessive genes, may result in serious disease or even offspring not surviving to term.  

For example, some dogs that are albino (their genes for producing melanin are inactive) are more prone to eye diseases, including reduced vision and light sensitivity. One study also found some albino dogs are more prone to eye and skin cancer. Dogs carrying two copies of the recessive d1 gene can develop an inflammatory skin disease called coat dilution alopecia that results in dry, sensitive skin and hair loss. The ‘merle’ colour is associated with many serious conditions, including eye disease and blindness, deafness, heart and reproductive disease – these are more commonly seen when two merle dogs are bred together. 

For someone wanting to purchase a dog, as well as the usual warnings regarding diseases specific to certain breeds, you should also take some time to research the possible diseases associated with certain colour dogs, particular unusual or ‘trendy’ colours.  

Further reading 

Gene | Definition, Structure, Expression, & Facts | Britannica 

How Many Genes Do Humans Have? | The Scientist 

Hair Follicle Pigmentation – PMC 

Genetics Basics: Coat Color Genetics in Dogs | VCA Animal Hospitals 

Genetics of pigmentation in dogs and cats – PubMed 

Canine coat pigmentation genetics: a review – Brancalion – 2022 – Animal Genetics – Wiley Online Library