Why Do Some Dogs Have Blue Eyes?
- Pieter Maas
Paths to Baby Blue – Blue eyes are found in a number of dog breeds, including Old English sheepdogs, border collies, and Welsh and Pembroke corgis, Irizarrypoints out. But for these breeds the blue-eyed trait is inherited as a recessive trait, meaning that two mutated copies of the gene are required for the blue eyes to occur.
In humans, he says, blue eyes are caused by a genetic variation between a pair of genes called HERC2 and OCA2 in the human genome. According to Irizarry, the mutation of the ALX4 gene in Siberian huskies seems to result in decreased pigment production in the eye. The lack of pigment causes the eye to appear blue.
“There’s no blue pigment. It’s about the way the light enters and exits the eye, creating the appearance of blue, the same way the sky looks blue but outer space is not blue,” says Irizarry. The type of mutation found in the study—in this case, the duplication of a snippet of genetic information—is also how tri-colored Australian shepherds sometimes end up with blue eyes, a phenomenon unexplained before this study, says one of its authors,Embark Veterinary, Inc.
What do blue eyes in dogs mean?
Page 4 – A blue eye in dogs is not a common occurrence, but it can happen. In most cases, the blue eye is a result of corneal edema, or when there is excess water in the cornea secondary to a disease process. The blue eye may be accompanied by other symptoms, such as discharge from the eyes or excessive tearing.
Do blue eyes mean deafness in dogs?
Congenital deafness in dogs (or other animals) can be acquired or inherited. Inherited disorders most commonly can be caused by a gene defect that is either autosomal dominant, autosomal recessive, sex-linked, mitochondrial, or may involve multiple genes (more on this later).
It is usually impossible to determine the cause of congenital deafness unless a clear problem has been observed in the breed, or carefully planned breedings are performed. In this article I will discuss what is currently known about the genetics of deafness in dogs so that breeders can make the best informed decisions possible when attempting to reduce or eliminate deafness.
Congenital deafness has been reported for more than 100 dog breeds, with the list growing at a regular rate (see list ); it can potentially appear in any breed but especially in those with white pigmentation of skin and hair. Deafness may have been long-established in a breed but kept hidden from outsiders to protect reputations.
The disorder is usually associated with pigmentation patterns, where the presence of white in the hair coat increases the likelihood of deafness. Two pigmentation genes in particular are often associated with deafness in dogs: the merle gene (seen in the collie, Shetland Sheepdog, Dappled Dachshund, Harlequin Great Dane, American Foxhound, Old English Sheepdog, and Norwegian Dunkerhound among others) and the piebald gene (Bull Terrier, Samoyed, Greyhound, Great Pyrenees, Sealyham Terrier, Beagle, Bulldog, Dalmatian, English Setter).
However, not all breeds with these genes have been reported to be affected. The deafness, which usually develops in the first few weeks after birth while the ear canal is still closed, usually results from the degeneration of part of the blood supply to the cochlea (the stria vascularis).
- The sensory nerve cells of the cochlea subsequently die and permanent deafness results.
- The cause of the vascular degeneration is not known, but appears to be associated with the absence of pigment producing cells known as melanocytes in the stria.
- All of the functions of these cells are not known, but one role is to maintain high potassium concentrations in the fluid (endolymph) surrounding the hair cells of the cochlea; these pigment cells are critical for survival of the stria and the stria is critical for survival of the hair cells.
A different form of congenital hereditary deafness is seen in the Doberman, which is also accompanied by vestibular (balance) disturbance; this deafness results from a different mechanism where hair cell death is not the result of degeneration of the stria but is instead the primary pathology.
Deafness may also occur later in life in dogs from other causes such as toxicities, infections, injuries, or due to aging (presbycusis); most of these forms of deafness do not have a genetic cause in animals and thus do not present a concern in breeding decisions, but a newly-identified form of adult-onset hereditary deafness is now recognized in Border Collies and Rhodesian Ridgebacks.
The prevalence of congenital deafness in different breeds is seldom known because of the limited number of studies (see table ). In the Dalmatian, where the prevalence is highest, 8% of all dogs in the US are bilaterally deaf and 22% are unilaterally deaf; rates are lower in Europe.
- In the English Setter, English Cocker Spaniel, Australian Cattle Dog, and Bull Terrier, where fewer numbers of dogs have been hearing tested, the prevalence appears to be about one third to one half that of Dalmatians.
- Unilateral or bilateral deafness is found in 75% of all white Norwegian Dunkerhounds, but the prevalence in normal-color dogs is unknown.
Other breeds with a high prevalence are the Catahoula and Australian Shepherd. The prevalence of all types of deafness in the general dog population is low, reported to be 2.56 to 6.5 cases per 10,000 dogs seen at veterinary school teaching hospitals, but these data predate the availability of hearing testing devices and so are much lower that actual values.
Recognition of affected cases is often difficult, because unilaterally deaf dogs appear to hear normally unless a special test (the brainstem auditory evoked response, BAER) is performed; facilities to perform the BAER are usually only available at veterinary schools (see list ). It should be noted that a unilaterally deaf dog can be as great a genetic risk for transmission of deafness to its offspring as is a bilaterally deaf dog, so BAER testing of puppies from affected breeds is important.
The method of genetic transmission of deafness in dogs is usually not known. There are no recognized forms of sex-linked deafness in dogs, although this does occur in humans. The disorder has been reported to have an autosomal recessive mechanism in the Rottweiler, Bull Terrier, and Pointer, but these suggestions are not reliable because the reports were published before the availability of BAER testing and the ability to detect unilaterally deaf dogs.
- Studies of the Pointer used a highly inbred research population (“anxious” Pointers), which can obscure the mode of inheritance.
- Some references state that deafness transmission in most other breeds is autosomal dominant, but this is false, as will be discussed below.
- Pigment-associated inherited deafness is not restricted to dogs.
Similar defects have been reported for mice, mink, pigs, sheep, horses, cattle, cats, ferrets, rabbits, llamas, alpacas, and humans. Deafness in blue-eyed white cats is common, first mentioned in Darwin’s Origin of Species, Blue eyes, resulting from an absence of pigment in the iris, is common with pigment-associated deafness but is not, in and of itself, an indication of deafness or the presence of a deafness gene; however, in several breeds (Dalmatian, English Setter, English Cocker Spaniel, Bull Terrier), dogs (and cats) with blue eyes are statistically more likely to be deaf.
Waardenburg’s syndrome, a human condition, presents with deafness, a stripe of white in the hair and beard, blue or different colored eyes (even in Blacks and Asians), no pigment behind the retina, and minor structural deformities around the nose and eyes. This is an autosomal dominant disorder with incomplete penetrance, which means that individuals that inherit the disorder may not show all components of the syndrome – i.e., they may not be deaf.
Incomplete penetrance of a defect greatly complicates the determination of mode of inheritance. At present there is no documentation that incomplete penetrance is a factor in any canine deafness, except perhaps that deafness can affect one or both ears.
In simple Mendelian genetics, each dog carries two copies of each gene, one from each parent. The possible outcomes of breedings can be demonstrated with tables showing the genotype of both parents and the possible combinations in their offspring. If deafness is carried as a theoretical simple autosomal recessive gene (d), the breeding of two hearing carriers (Dd) ( Table 1 ) will result, on average, in 25% affected dogs (dd), 50% hearing carriers (Dd), and 25% free of the defect (DD).
It must be emphasized that these percentages reflect average breeding outcomes and not necessarily every individual litter. The breeding of a carrier to a dog free of the defect ( Table 2 ) will result in no affected dogs but 50% carriers and 50% free.
The breeding of an affected dog to a carrier ( Table 3 ) will result in 50% affected, 50% carriers, and no free. Finally, the breeding of an affected dog to a dog free of the defect ( Table 4 ) will result in 100% carriers and no affected or free. If instead the deafness is carried as a simple autosomal dominant gene (D), the breeding of an affected dog (Dd) to a free dog (dd) ( Table 3 ) would result on average in 50% affected and 50% free.
Dogs with the genotype DD would be unlikely to occur unless two deaf dogs had been bred. All of the above assumes that incomplete penetrance is not acting. If more than one gene (recessive and/or dominant) is involved in producing the deafness, the possible combinations become much more complicated.
- In humans more than 50 different autosomal recessive or dominant deafness genes or loci have been identified.
- The children of two deaf parents with two different recessive deafness can be unaffected but carry both genes.
- If deafness in dogs results from more than one recessive gene, the possible outcomes of breedings are more numerous and determination of the mechanisms of transmission will be difficult.
As stated above, deafness can be associated with the merle (dapple) gene, which produces a mingled or patchwork combination of dark and light areas overlayed on the basic coat color. This gene ( M ) is dominant so that affected dogs ( Mm ) show the pigmentation pattern, which is desirable in many breeds.
- However, when two dogs heterozygous with merle ( Mm ) are bred, 25% will end up with the MM genotype (i.e., Table 1 ).
- These dogs usually have a solid white coat and blue irises, are often deaf and/or blind, and may be sterile.
- Breeders in these dog breeds know not to breed merle to merle.
- In this case the deafness is neither dominant nor recessive, but is linked to a dominant gene that disrupts pigmentation and as a secondary effect produces deaf dogs.
Piebald is a recessive allele of the S gene, where the dominant allele is expressed as a solid color. Three recessive alleles are recognized: Irish spotting ( s i ), piebald ( s p ), and extreme white piebald ( s w ). These gene alleles affect the amount and distribution of white areas on the body, with the three displaying increasing amounts of white in the order listed.
Genetic transmission of deafness in dogs with the recessive alleles of this pigment gene, such as the Dalmatian (which is homozygous for s w ), is less clear. Deafness in Dalmatians does not appear to be autosomal dominant, since deaf puppies result from hearing parents. It does not appear to be a simple recessive disorder, since we have bred pairs of deaf Dalmatians and obtained bilaterally hearing and unilaterally hearing puppies, when all should have been deaf if the disorder was recessive.
These findings might be explained by a multi-gene cause – the presence of two different autosomal recessive deafness genes, or a syndrome with incomplete penetrance. Further studies will be required to determine the mechanisms. Several candidate genes known to cause pigment-related deafness in humans or other species have been eliminated as the possible cause of pigment-associated deafness in Dalmatians.
Whole-genome screens will hopefully identify the cause in this and other breeds. Recent studies have shown that deafness in Dobermans, which do not carry the merle or piebald genes, results from direct loss of cochlear hair cells without any effects on the stria vascularis. Vestibular (balance) system signs, including head tilt and circling, are seen, and the deafness, which is usually bilateral, is transmitted by a simple autosomal recessive mechanism.
A similar pathology has been described for the Shropshire Terrier, a breed that may no longer be in existence. So what should breeders do when deafness crops up? The most conservative approach would be to not breed the affected animal and not repeat the breeding that produced deafness.
- It is frequently recommended (i.e.
- Dalmatian Club of America ) that bilaterally deaf puppies should be euthanatized by breeders, since they can make poor pets, are difficult to train, can be prone to startle biting, may die from misadventure (cars), and require excessive care.
- There is considerable controversy on this point, and there is no question that many people have successfully raised deaf dogs.
For every story of a problem deaf dog there seems to be a story of one that was successfully raised. Unfortunately, there is no way to predict how a deaf puppy will turn out. Unilaterally deaf dogs can make good pets but should not be bred. When deafness is uncommon in a breed, affected dogs should not be bred, but this does not mean that all related dogs are a risk and must be retired from breeding.
An understanding of simple autosomal recessive and dominant patterns, as explained above, can allow the breeder to make better informed decisions (even though we do not yet know the mechanism of inheritance) and likely avoid future deaf animals without sacrificing a breeding line that has been shaped over many years.
However, extreme caution must be used when line breeding of dogs related to deaf dogs, whether the deafness is unilateral or bilateral. To make these decisions in an informed manner for breeds with known deafness, it is important that advantage be taken of hearing testing facilities at veterinary schools.
Unilaterally deaf dogs cannot be detected by other means, and these dogs will pass on their deafness genes. For more details and a more technical discussion, see: Strain G.M. (2015) The genetics of deafness in domestic animals. Fronteers in Veterinary Science 2:29. ( https://www.frontiersin.org/articles/10.3389/fvets.2015.00029/full ).
This article is available on-line and is free.
Do blue eyes have disadvantages?
These Are 10 Blue Eyed Dog Breeds
One Common Ancestor – According to recent studies, people with blue eyes have a common ancestor, The new research has tracked down a genetic shift that leads to blue eyes. This significant research shows that the gene mutations affected the OCA2 gene.
- This gene is involved in producing the pigment (melanin) that creates the color of eyes, hair, and skin.
- The genetic shift turned down the ability to produce brown eyes, resulting in the creation of eyes with less pigment (blue eyes).
- Over time, some of the elements of the genes change while others remain unchanged.
The unchanged segments are called haplotypes, When individuals share these haplotypes, scientists believe that it shows common ancestry. In recent studies, scientists are showing that people with blue eyes in Denmark share the genetic traits of people as far as Jordan.
Do dogs understand kisses?
Kissing is such a natural thing for many humans, yet have we considered what that gesture means to our canine friends? – In many cultures kissing another person is primarily seen as a sign of affection or, for some cultures, it is simply a positive gesture. For many pet owners giving their pups a kiss and a cuddle is something that comes as second nature, but what do dogs make of this? Dogs cannot pucker or purse their lips. They can move their lips somewhat but do not have the lip muscles or range of lip movement as people do. Just like they cannot chew food with their mouths closed, as we do. If it is not natural or native to them, like many gestures that humans do, they need to figure out what it means.
- Is it a good thing or a bad thing? From a human perspective As humans, we expect our dogs to sometimes behave in human-like ways and we therefore may subject them to things that aren’t a normal part of their behavior repertoires.
- Some of us dress up our dogs, teach them to shake hands with people and even expect them to not pass gas in front of guests.
On top of this, we may expect dogs to cherish being kissed and hugged. From a dog’s perspective When a dog is kissed, it means bringing our face very close to the dog’s face, and this is something that not all dogs are comfortable with. From a dog’s perspective, putting our face close to their faces and plastering them a kiss on the nose, mouth or forehead, may be perceived as a bite or attempt to bite.
When we hug and kiss our dogs, we may also wrap our arms around them which removes the dog’s “flight’ option” (the ability to leave). When we hug and kiss dogs, we may therefore put ourselves at risk for a defensive bite to the face which can be very dangerous. Studies have shown that bending over a dog, putting the face close to the dog’s face and making eye contact (all behaviors taking place when kissing a dog), often led to bites directed towards the central area of the face.
Sadly, according to the study, more than two thirds of the victims were children. Young children often perceive dogs as stuffed animals. They want to hug them and smooch them as they do with their toys. Perspectives can change According to Animal Behaviorists, ‘ dogs don’t understand human kisses the same way that humans do.’ When kissing a young puppy, you may not notice any signs of recognition at all because they have yet to associate kisses with affection. Dogs may respond differently to being kissed and hugged. Some dogs love it, others show pretty obvious signs of disliking it, and some just tolerate them. Some dog owners claim that their dogs seem to really enjoy it, but is that the real picture? In some cases, dogs may be showing very subtle signs of discomfort that go unnoticed, like pulling away or turning away, some even snarl or grumble.
Do dogs actually smile?
Why Do Dogs Smile? – Most experts agree dogs smile in response to the human smile. Dogs seem to smile more when relaxing, playing, feeling content or greeting someone they know. Dogs don’t smile in response to a joke, but they may smile in response to you.
Usually, when a dog smiles it is known as a submissive grin. The dog’s posture is relaxed and teeth are exposed. It is important to note the exposure of teeth is not always a sign of aggression like some people may believe. Most animal behaviorists see a canine smile as an adaptive facial expression and behavior with a range of functions and benefits.
Dogs seem to display smiling as a social skill and expression of emotion. Humans reward smiling when we react, laugh, give treats, pet and clap. Dogs quickly learn there will be a positive reaction so will continue smiling in order to receive positive reinforcement.
Can dogs see themselves in mirror?
The dogs moved off a mat that had a toy attached to it, showing that dogs may understand their body size and where they are in the environment when solving a task. Rita Lenkei / ELTE Anecdotally, dogs may not seem very aware of their size and how much room they take up—try sharing your bed with a dog of any shape or size and this becomes clear.
- Puppies sometimes like to jump at new people, unaware of their increasing strength, and plenty of big dogs insist on being lap dogs well past the puppy stage.
- So, the results of a new study published last week in Scientific Reports claiming to provide the ” the first convincing evidence of body awareness” in dogs may surprise you.
Body awareness is key to establishing self-awareness or self-representation, which means an individual has the capacity not only to perceive themselves but also perceive where they are in space, Yasemin Saplakoglu explains for Live Science, Researchers at Eötvös Loránd University in Budapest add canines to the list of animals, including humans, that seem to understand how their bodies move through the world around them, reports Carly Cassella for Science Alert,
- Dogs are perfect subjects for the investigation of the self-representation related abilities as we share our anthropogenic physical and social environment with them.
- Thus, it is reasonable to assume that at least some of its forms might appeared in them, too,” says study author Rita Lenkei, a graduate student, to Chrissy Sexton for Earth.com,
Adapting experimental methods from studies of body awareness in elephants and toddlers, the researchers tested 32 dogs of different breeds and sizes on their ability to recognize their body as an obstacle. In the problem-solving experiment, the canines had to grab a toy that was attached to a mat they were sitting on.
- If the dogs demonstrated body awareness, they knew they needed to get off the mat to complete the task and give the toy to their owners, reports Live Science,
- The experimental conditions were then compared to control groups in which the toy was attached to the ground or wasn’t attached to anything at all, reports Science Alert,
The dogs quickly moved off the mat with a toy attached more often than they did when the toy was stuck to the ground instead. “When dogs pulled on the toy, it also started to lift the mat — thus the dog felt that the mat was jerking under its paws as it was pulling the toy.
- In this scenario, the dogs quickly left the mat, usually still holding the toy in their mouth; then they gave it to the owner,” says Péter Pongrácz, a biologist at Eötvös Loránd University, to Live Science,
- In the past, dogs have been tested for their sense of self-awareness through methods that the researchers thought were not “ecologically relevant.” Dogs fail to recognize themselves in the mirror mark test, for example, in which scientists place a visible mark on an animal’s face to see whether they will investigate it in a mirror.
Other species, like elephants and great apes, are mirror-mark-test masters, Live Science reports. Although dogs can’t identify themselves in the mirror, they still have some level of self-awareness and ace other self-recognition tests. They can recognize their own odor, and recall memories of specific events, Earth.com reports.
This past evidence led the researchers to suspect canines show a lower level of self-representation that can only be observed in simpler tests that focus on their body and environment, explains Pongrácz to Catherine Offord in an interview with The Scientist, “For a dog, being aware of how big is the body, or how the body can be an obstacle, it’s reasonable to expect.
This is an animal with a complex nervous system, it’s an intelligent animal, it’s a fast-moving animal. If you think about how dogs eat, you can imagine that a dog often has to hold down a bigger chunk of food, let’s say, and use its own body as a counterweight to be able to take off meat from a bone or whatever.