Thursday, August 28, 2014

Cool Animal Sounds: Cheetah

Cheetahs are unusual for a big cat in that they cannot roar. Perhaps the most well known of the sounds they do make is a chirp, which sounds rather astonishingly like a bird. This noise is used as communication between mothers and offspring, but has been observed in some other situations.

Cheetahs can also purr (in cats there is a purr versus roar dichotomy), hiss, and produce a number of other vocalizations. A "stutter bark" unique to males has been linked to the complexities of cheetah ovulation. Vocal-induced ovulation is not common in mammals, so it's no wonder keepers failed to figure out why their captive cheetahs weren't breeding.

Sources and Further Reading: National Wildlife Federation, National GeographicVolodins Bioacoustic Group, Animal Diversity Web,, An acoustic analysis of purring in the cheetah (Acinonyx jubatus) and in the domestic cat (Felis catus), A comparative acoustic analysis of purring in four cheetahs, A comparative acoustic analysis of purring in juvenile, subadult and adult cheetahs

Wednesday, August 27, 2014

Nearly Wordless Wednesday: Scary-eyed Blond

Ginger-root, fawn/dominant yellow/lethal yellow fancy mouse, satin coat, pink eye dilute.

Because of some confusion, I'm not going to make these completely wordless. 

Friday, August 22, 2014

Ebon's First BarkBox!

My mother was kind enough to gift Ebon with a six month subscription to BarkBox and the first one arrived today! I quite like the idea, but haven't been able to subscribe. The greyhounds are also getting a box. So, what came this month?

This is how my silly boy plays

Loopies Floppy Fishbone

Company link: here Note: this toy is not currently on their website
The toy is made of polyester and has a single squeaker at one end. The stitching looks durable and it's low on easily chewable bits, which should help it hold up to rougher pups. Though Ebon stopped destroying his toys some time ago, I wonder how it will hold up to Willow, who is not so restrained as of yet. As Ebon is quite fond of squeaky toys, it was an immediate hit. He did his "happy dance" where he rolls around on his back while squeaking the toy like mad. 

Bixbi Daily Essentials Chicken Breast Jerky Treats

Company link: here
Ingredients: Chicken breast, blueberries, cranberries, organic reishi mushrooms, vegetable glycerin
Guaranteed Analysis: 
Crude Protein: 71.89% minimum
Crude Fat: 3% minimum
Crude Fiber: 5% maximum
Moisture: 9.22% maximum

This is the first dog product I've ever found that includes muchrooms, which I find quite interesting. The jerky is slightly soft, breaking very easily into smaller pieces, a trait I generally like as I usually prefer to treat in smaller portions. They do not have a particularly strong smell, being faintly meaty with a hint of mushroom. Ebon was quite excited to try one as he never turns down chicken. 

Healthy Dogma Coconut Barkers

Company link: here
Ingredients: Peas, pea flour, potato, tapioca, coconut, canola oil (preserved with mixed tocopherols), pumpkin, cranberry powder, cinnamon
Guaranteed Analysis: 
Crude Protein: 12.0% minimum
Crude Fat: 5.0% minimum
Crude Fiber: 4.50% maximum
Moisture: 12.0% maximum

These treats are grain free and also meat and other animal product free, which can be a bit unusual for a dog treat. They smell pleasantly of coconut. Like most crunchy treats, they snap easily into smaller pieces. Ebon was quite happy to gobble them up as he is quite fond of crunchy treats. 

Etta Says! Crunchy Duck Chew (12 Inch)

Company link: here
Ingredients: Rawhide, duck feet, natural caramel color, salt
Guaranteed Analysis: 
Crude Protein: 52% minimum
Crude Fat: 20% minimum
Crude Fiber: 4% maximum
Moisture: 10% maximum

I somehow managed to miss getting this in the photograph, but there was one twelve inch chew. The chew smells pretty standard for an animal product chew, a bit smokey and of collagen. It breaks easily into smaller pieces, so if the box is being shared between multiple pups it can be easily split. Ebon has had duck feet before, so I'm sure it will be a big hit. I'm saving it for later. 

Mr. Barksmith's Cool Treats Smoothies for Dogs

Company link: here 
Ingredients: Apple puree, banana puree, water, natural pina colada flavor
Guaranteed Analysis:
Crude Protein: 0.41% minimum
Crude Fat: 0.38% minimum, 0.45% maximum
Crude Fiber: 1.30% maximum
Moisture: 86.80% maximum

I've tried out a frozen treat before and even made some myself. Since Ebon likes to eat ice cubes when we throw some in his bowl in the heat, he definitely enjoys something cold with a little more interest! Ebon likes both banana and apple, and after the coconut treats that came in this box I'm sure he'll enjoy the coconut too. We've been having a heatwave for days now, with the heat index during the day well over 100°F and at night often barely dipping below 90°F. Ebon is going to really appreciate his cool treat as soon as it's finished freezing. 

One happy dog

Tuesday, August 19, 2014

Mismark Case Study: Great Dane Revisit and Expansion

The first mismark case study I ever did was of the great Dane. To a large extent that post was incomplete, so I started from scratch. This took me an embarrassingly long time to put together, but I was determined to finish it before doing anything else.
A group of great Danes, two in standard colors (fawn and mantle) and two in non-standard colors (merle mantle and "true" blue merle aka dilute merle). Image is from under a Creative Commons License
Of all breeds that I have looked at, the great Dane breed color standard makes the least amount of sense. While most will restrict a few colors, often recessives or minor aesthetic differences such as eye color, the Dane standard is much more restrictive. Using only the genes that go into making the six "acceptable" colors (fawn, brindle, black, blue, mantle, and Harlequin), there is a significant list of non-standard colors that could occur simple by breeding between those six standard colors. This has lead to color class breeding. For people who breed show Danes, those color classes are a way of life. What are the color classes? According to the Great Dane Club of America, there are four of them. Breeding between these classes is severely frowned upon and there is potential that it could lead to expulsion from the breed club.

Fawn and Brindle
Breeding of fawns and brindles to other fawns and brindles whose pedigrees are free of black, blue, or Harlequin
Breeding of blues to other blues or to "blue-bred blacks" whose pedigrees are free of fawn, brindle, or Harlequin. A blue or blue-bred black can also be bred to a black-bred black
Breeding between mantles, Harlequins, and "Harlequin-bred blacks." It is also acceptable to breed a dog from this class to a black-bred black. Any combination is acceptable so long as the pedigrees are free of fawn, brindle, or blue. This includes the pairing of two Harlequins.
"Black-bred blacks" come from generations of exclusively black to black breeding, resulting in pedigrees free of blue, fawn, mantle, brindle, or Harlequin.

Even breeding within these classes does not eliminate mismarks, with more than a few breeders being surprised when, for example, they pair a mantle with a five-generation pedigree fitting the Harlequin class to another mantle of the same designation and produce a blue mantle or fawn mantle. This is not even getting into the flaws with Harlequin in and of itself.

The Mismarks:

This great Dane is a merle mismark, one of the most common seen in the breed.
Bolded are standard colors and green are non-standard colors produced ONLY from genes that go into the standard colors. I've omitted Harlequin + mantle and similar as they can be visually indistinguishable from dogs without.

add Irish white MantleFawn mantleBrindle mantle
add dilute BlueBlue fawnBlue brindle
add Irish + dilute Blue mantleBlue fawn mantleBlue brindle mantle
add merle MerleFawn merleBrindle merle
add merle + dilute Blue merleBlue fawn merleBlue brindle merle
add merle + Irish MerlequinFawn merle mantleBrindle merle mantle
add merle + Irish + dilute Blue merlequinBlue fawn merle mantleBlue brindle merle mantle
add merle + Harlequin modifier HarlequinFawnequinBrindlequin
add merle + Harlequin + dilute Blue HarlequinBlue fawnequinBlue brindlequin
add merle + merleDouble merle replaces single merle. Causes an increase in white.
Has a high likelihood of deafness, blindness, and/or eye abnormalities.
add merle + merle + HarlWhite. Most whites have virtually no color.
Has the same health concerns as double merle. 
add liverChocolate acts like dilute, replacing black.
This includes masks on fawns and stripes on brindles
add liver + diluteBlue and chocolate combine to make Silver
Silver replaces chocolate, dilute, or black 
add piebaldPiebald would replace Irish in the above combinations.
Both piebald and extreme white piebald are possible

Tan on this Dane is consistent with a seal
This great Dane has no mask
All of these colors are recognized as existing by the American Kennel Club so, unlike with some breeds, the vast quantity of potential mismarks are well known to exist. Fitting (mostly) within the above chart are subsets that would severely penalize or disqualify an otherwise acceptable color from conformation: bad black (aka seal), improper pigmentation (usually a pink-nosed Harlequin) and white on a blue, black, fawn, or brindle (some is allowed, but not preferred). Although unusual, there have been instances of tan pointed and maskless great Danes as well. Ticking sometimes happens, but, for the AKC at least, there is no mention of whether it would be penalized or not.

So, what causes all of that, anyway? 

As can be seen in the chart above, a very large number of mismarks can occur when only looking at the genes that make the six standard colors.

This puppy is a Brindlequin mismark
Perhaps the biggest indicator of color in great Danes is the K locus, which codes for black and brindle. Black (K) is most dominant, followed by brindle (kbr), and then non-black/non-brindle (k). Since a black dog only needs one copy of the dominant K gene to be black, it can easily carry either brindle or fawn as Kkbr or Kk, respectively. When the right two dogs come together, a litter that was expected to be all standard black mantles could throw something unexpected. When homozygous for the non-black/brindle allele (kk), the agouti locus will show through unobstructed. For most Danes, this will make them fawn, but this would also be why the tan pointed or even brindle pointed Dane appears. In the case of brindle points, the agouti locus is still peaking through, but it is obscured by the brindle overlay.

Referring back to the chart, it's quite clear that most of the standard Dane colors are black-based. Black, mantle, and Harlequin all have obvious black on them, while blues are genetically dominant black with the extra quality of also being diluted. Due to the black base of all of these colors, if a dog inherits a gene combo that does NOT code for black (kbrkbr, kbrk, or kk) then it would have either brindle or fawn instead of black. This includes Harlequins (turned to brindlequin or fawnequin) and mantles (turned to brindle mantle/brantle or fawn mantle/fawntle).
This dog is a heavily marked blue Harlequin

Blue/dilute is a simple recessive gene inherited on the D locus, with the dog having to receive two copies (dd) for it to show. Dilute affects all black in a dog's coat, turning it to some shade of gray. This includes masks and stripes in brindles. Even if trying to only breed the dominant variant of a gene, there is no guarantee that the recessive form will disappear. This is why diluted variants such as blue Harlequin (aka porcelain) continue to pop up from parents whose pedigrees may have not seen a blue for decades.
This Dane is a fawn mantle mismark

The A (agouti) locus is probably the most varied locus in the dog world, but in great Danes there appears to be only two variations, with the breed being nearly fixed for one of them. Being fixed for a gene means that no other genetic variants are seen at that locus. Sable (Ay), which causes Fawn, is the most dominant of the agouti variants and tan point (at) one of the recessive variants. Considering the low incidence of tan point, great Danes can, for the most part, be treated as if they were fixed for sable due to there not being many tan point carriers.

Fawn and brindle great Danes are also known for having black masks. This is inherited independently on the E locus, aka the extension locus. The most dominant of the extension genes is, indeed, the mask gene (Em). Considering that maskless Danes do exist, some other variation has to exist, but it can be difficult to tell whether that would be recessive red (e, which strips away all black in a coat, leaving it entirely red) or the "null" allele of non-masked, non-everything-else (E). There is some evidence for both but, like with the agouti locus, the breed appears to be near fixed for one allele. In this case, that's the mask gene.

This dog is a dark blue mantle mismark
Mantle comes from recessives on the S (spotting) locus. White spotting varies significantly from virtually no white to virtually all white. Blue, black, fawn, and brindle Danes must have at least one copy of the solid (S) allele. If carrying Irish white (si), piebald (sp), or extreme white piebald (sw) a dog will likely have at least a small amount of white due to the semi-dominant nature of the spotting genes. This is usually on the chest and/or toes, but may also lead to a white tail tip or some facial white. A dog with white, however, does not necessarily carry any of the recessive variants. Residual white is quite common in genetically solid (SS) dogs due to how color migrates during very early development. It essentially spreads from the spine to the extremities in the womb, so if the color doesn't spread all the way, a dog will be born with some amount of white. As with many breeds some white is allowed on otherwise solid Danes, but too much is penalized.

This great Dane is a piebald merle
To be mantle, a dog's phenotype must have more white than what is possible from a homozygous solid dog. The white required by the breed standard is essentially Irish white, a pattern most people associate with breeds such as the border collie. This appearance can come from several variations of the spotting locus. As expected, a dog can be homozygous for the Irish white variant (sisi), but a dog carrying piebald (sisp) will look similar, though possibly with a little more white. Since the standard allows white to break the main body of the dog, some Danes who fit the standard appear to be minimal piebalds (spsp).  In addition, pseudo Irish white, caused by either a solid carrying extreme white (Ssw) or what would have been a low-white Irish carrying extreme white (sisw), will look like a homozygous Irish dog.

I've met a dog much like this extreme white Dane
Due to the vast amount of variation in the potential genotypes that would lead to the acceptable mantle phenotype, it isn't surprising that piebalds and extreme white piebalds are known to pop up in the breed. As extreme white is more common, it's likely there are a lot of pseudo Irish dogs out there.

In addition to the vast quantity of potential for mismarks seen above, there is the illogicality of the nature of breeding for Harlequins. Harlequin can, by its nature, NEVER breed true. It is a color caused by a very specific combination of two problematic genes. One of them is merle (M), which is well known to cause serious issues when a dog inherits a double dose of the gene. Harlequin (H) is, in some ways, worse than merle. While double merles are generally viable despite the high incidence of deafness and/or blindness, double Harlequins are lethal in utero. Since no living dog can be homozygous for Harlequin, this explains why merle dogs are to be expected in every litter with at least one Harlequin parent. The worst part of Harlequins, however, is that breeding a Harlequin to another Harlequin is perfectly acceptable under color class breeding. This is a serious problem.

Here is a Punnet square for a Harlequin/Harlequin cross:
double double

double Harlequin merle

double merle Harlequin
possibly deaf/blind

double Harlequin merle

double Harlequin


black or mantle
carrying Harlequin
double merle Harlequin
possibly deaf/blind


double merle
possibly deaf/blind

merle or merle mantle

black or mantle
carrying Harlequin

merle or merle mantle

black or mantle

This white Dane is deaf.
When crossing two Harlequins together, the assumption is that the breeder wishes to produce more Harlequins. Considering this, a 25% chance of a Harlequin is pretty bad when the price to pay is the likelihood one-in-four of the puppies will never even have a chance to live and another 18.75% of embryos have a very high chance of being blind and/or deaf. That's almost half the litter! Some breeders cull double merles, but this is a shameful practice, sweeping poor decisions under the rug in the form of dead puppies. The alternative, however, isn't exactly wonderful. Due to their sheer size, only so many people are willing to adopt a great Dane. When that size comes with impaired senses, the number of available homes plummets. A dog that is deaf and/or blind is significantly more difficult to train than a dog with full use of its senses, and a huge, poorly trained dog can be very difficult to deal with. I once met a deaf great Dane at my local dog park who would not stop humping my Labrador. My poor dog barked at him in frustration, but, being deaf, the dog had no awareness of such social cues. If my dog wasn't so even-tempered the Dane could have easily been injured due to his poor social skills. Since the Dane's owner wasn't leaving, I understandably removed my dog from the situation.

Many assume that white great Danes are albinos, but their lack of pigment is caused by a very different set of circumstances. As breeding from a merle is not acceptable in color class breeding, whites come from Harl/Harl crosses like the one above and, as they are double merles, they have a high risk of sensory issues. Some may be very lightly marked Harlequins, but this is unlikely. I have also seen at least one dog that appears to be an extreme white piebald Harlequin, but this is also not the most likely phenotype. What patches you do see on white great Danes will usually be solid black, but just as fawn mantle and blue Harlequin can occur, you can also get double merle Harlequins of a different color as well.

In contrast to the Harl/Harl cross, here's a Punnet for a Harlequin/black cross where the black does not carry the Harlequin modifier:


black or mantle
carrying Harlequin

merle or merle mantle

black or mantle

This cross has the same 25% chance of producing a harlequin, but there is a 0% chance of color-related non-viable embryos and a 0% chance of double merles, so the breeder will not have to find homes for deaf and/or blind dogs. There will still be merles, but since the Harlequin modifier is lethal in a double dose, this is an inevitable consequence of Harlequins.

This great Dane is a merle mantle mismark
Since merle is never going away, the absurdity of making it a disqualification is rather remarkable. In most breeds, colors that pop up with the high frequency of merles in great Danes are generally accepted by the standard. In addition, why does the Great Dane Club of America allow Harlequin/Harlequin cross when crossing a merle with a black that's been tested positive as a carrier for the Harlequin modifier is frowned upon? Both have the potential to produce Harlequins, but the merle cross, like breeding a Harlequin to a non-carrier black, doesn't have the issues that a Harlequin/Harlequin cross does. Mantle became an accepted breed color because of Harlequin breeding. I don't see why merle shouldn't be treated the same way.

This puppy is a chocolate fawn
This portrait is believed to include a Dane
The last color determinant I have not discussed is the B locus. Brown/liver acts much like the blue dilution. It's a simple recessive (so all dogs expressing it are bb) that turns any black in the dog's coat from black to some shade of brown. Like dilute, any dog with black can have liver coloration instead. In great Danes, liver is known as chocolate. It can also act in combination with blue, diluting down to Isabella (also known by names such as silver, gray, ash, pearl, lilac, and fawn). Weimeraners are well known for their Isabella color. In great Danes, it appears that Isabella is known as either silver, lilac, or dilute chocolate. There is some evidence that chocolate was once an acceptable color in the breed that since fell out of favor, and the seventeenth century portrait at right is interesting in relation to this possibility. If the dog is in fact a very early great Dane or Dane relative, it isn't any color that would be found in a modern show ring. It appears to be an Isabella mantle.


Of all the breeds I have looked at, the great Dane is most problematic in terms of its color standard. It's one thing for a breed to have a number of recessive colors that show up on occasion, but on top of that Danes have mismarks that are guaranteed to occur when breeding one of its six acceptable colors. Also problematic are the color classes, which essentially create breeds within breeds. All purebreds have limited gene pools due to closed registries. Color classes take that genetic variation and limit it again. Since closed registries prevent any new genetic variation from being added, what there is cannot be replaced once it's gone. Genetc variation is essential to a healthy animal, allowing their immune system to function effectively. The less variation, the less functional the immune system.

With the limited variation that comes with closed registries, selective breeding is like taking a weed-wacker to a spindly bush. It can only take so much before there isn't enough of it left to survive. That is essentially what is occurring in modern dog breeds, where effective populations sizes are worse than what is considered at risk of immediate extinction in endangered species. Since the great Dane has such major restrictions in color acceptance, there is a massive amount of potential for loss in genetic variation that could have otherwise been saved.

Images in this post are from or Wikimedia Commons with the exception of the heads used in the Punnett squares, which were created by me. Everything is under a Creative Commons license and source links can be found beneath each image. 

Thursday, August 14, 2014

Why I Don't Like Retractable Leashes

A retractable leash
I have a neighbor with a reactive Doberman that is walked on a choke chain and a retractable lead. Clearly, someone has a fundamental misunderstanding of what these things are for, and it isn't the dog. That's what inspired this post.

They're Comparatively Expensive and They Break Easily

Almost all retractable leashes are twice the price of a standard leash of a comparable weight class (i.e. the strength needed for a dog of a certain weight). This isn't surprising as they're significantly more complicated, with multiple moving parts, while a standard leash in its simplest form only needs sewing or riveting in two places. One major consequence of this increase in complexity is the risk of one of the moving parts failing and rendering the "retractable" part of a retractable leash nonfunctional. There have been more that a few instances of retractable leashes failing very shortly after purchase. In comparison, unless your dog has a penchant for chewing whatever is attached to its neck, a standard leash can last decades before needing to be replaced from wear.

As a Training Tool, They are Virtually Useless

Don't get me wrong, there are very specific scenarios when a retractable lead would be useful. However, it should never be a person's default leash choice, let alone one to try to use to teach good leash manners. Corrections are virtually impossible, often resulting in encouraging misbehavior instead of preventing or alleviating it. The point of a leash correction is to redirect unwanted behavior. The best redirection in my experience is turning away from whatever stimulus is causing misbehavior. If a dog is moving toward something of interest and pulls a leash taught, it's easy to real them in with a standard six foot leash. With a retractable leash, however, there is much more distance in the leash itself and the internal mechanisms do not have an automatic rewind. As the length of the leash is thin in comparison to a standard leash, it is harder to get a firm grip on the material. If one tries to use the retractable nature of the lead to reel the dog in, it isn't difficult for the dog to instead gain more distance from its handler. I have seen this occur on multiple occasions. There are reasons why trainers do not use retractable leashes during sessions.

Every dog I have ever seen walking on a retractable leash has been very badly behaved. Not only is there the reactive Doberman, but there are also two highly aggressive Yorkshire terriers owned by another neighbor. Those two are far worse, most likely because whenever another dog is near their owner will pick them up. I saw one of them turn from a reasonable little dog to just as awful as her housemate, snarling and nearly biting her owner trying to get to my dog.

They'll Probably Make Other People Hate You

From experience, I immediately become wary of two kinds of behavior in another person and their pet when I'm walking my dog. The first is a taught leash with a dog pulling forcefully against its collar or harness. The second is the use of a retractable leash. (Of course there are always off-lead dogs, but as I'm in a city I don't expect to see them.)

Seeing this coming at me on a walk is my worst nightmare
Both of these scenarios are very unpredictable as it can be quite hard to say how the strange dog will react when in close quarters with another dog. The first scenario is a common concern for dog owners. Running at someone like a steam engine is an aggressive behavior and until they're nose to nose there's no real way to tell whether the pulling was from excitement or territoriality. The last time I had a dog come at me like that he attacked my dog.

As retractable leashes encourage unrestricted movement, making it nearly equivalent to a dog running free. It is more likely for a dog to use that sense of freedom to charge at a strange dog. Since this is indeed aggressive behavior, there is a good chance that this will lead to a confrontation. Another concern is what the leash will do if and when it pulls taught. As I said, they are prone to breakage and most dogs on this sort of leash are usually poorly behaved.

Most Importantly: They're Very Dangerous for Everyone Involved

There is a good reason why they come with warnings. The thin material of the retractable leash can cause severe injuries if it becomes wrapped around any body part and then pulled taught. These vary from burns and cuts to complete amputations, particularly of fingers. The leach can also be a tripping hazard, especially the thinner lines which may be difficult to see if the handler and dog are a significant distance apart.

A dog running at full steam on a retractable leash poses huge dangers to potentially everyone nearby. The sudden jerk when the dog reaches the end of the leash can cause serious injuries to the neck. Not only that, but an owner can be pulled off of their feet and dragged. The leash handle is also very easy to let go of due to its bulkier build. Then, the dog is running free. The sound of the handle hitting the ground can be quite frightening, but even worse is being "chased" by the handle after trying to run away. The dog can easily dart out into traffic or be exposed to other dangers, such as other dogs. Depending on the temperament of the dog, it can also expose a danger to other dogs or people.

All in all, unless you have a very (and I mean amazing bombproof very) well behaved dog, just stick to a standard leash. They're cheaper and safer and make it easier for everyone in your community to live without the need confrontation. 

Images are from and are under Creative Commons licenses: 1, 2.

Wednesday, August 13, 2014

Guess the Genotype #90

I'm going to be working on catching up on my lengthy backlog of GtG requests and suggestions.

Can you guess this dog's genotype? Its breed? Click read more to see my guess.

Images were provided by Lisa at San Antonio Pets Alive!

Tuesday, August 12, 2014


Two variants of the agouti gene: yellow on the left and a wild type on the right
Pleiotropy is a consequence of genetics that many people are not aware of. Specifically, this is when the most obvious characteristic caused by some genetic variant is not the only trait that is caused by the gene. Frequently, these characteristics seem like they would be completely unrelated, but it is surprising how many examples there are of vastly different traits being due to a small change in an organism's genetic code.

My three mice: Pepper (black piebald longhair), Poppy (black piebald, wild coat), and Ginger (lethal yellow satin)
Ginger before her weight gain
In May I brought home three fancy mice, having wanted to own a small mammal for quite some time. I chose my trio or females from their litter based on who came to me first, so it's just chance that I brought home a dominant yellow. Dominant yellow is also known as lethal yellow due to embryos that are homozygous dominant becoming nonviable very early in their development. As I only had very cursory knowledge of the amazing amount of variation in fancy mice before bringing my three home, I did not find out some of the interesting pleiotropic effects of the lethal yellow gene until I noticed something that distressed me. While her sisters were maintaining healthy body weights, my yellow looked very fat in comparison. After weighing them, I was surprised to find that, while her sisters were in fact right at the ideal thirty gram weight, my yellow weighed a whopping forty grams.

Lethal yellow is a gene that has been used rather heavily in scientific research. Why? Along with the golden coat, this form of yellow causes obesity, insulin-resistant diabetes-like traits, and an increased likelihood of developing tumors, among other things. Understandably, this has lead to lethal yellow lab mice being used in the research of diabetes. Interestingly enough, unlike some other mouse colors, dominant yellow had existed among fancy mice for a very long time, their usefulness for research only discovered some time later.

At first glance, most people would look at a dominant yellow mouse and say, "Isn't that pretty!" without having any idea of what else that color means. If I had previously known what this color meant, I might have decided against bringing my lethal yellow home. In all likelihood, she will live a shorter life than her sisters due to the pure chance of her being born a dominant yellow. 

Thanks to its blue eye, this cat is probably deaf in one ear.
In cats, one of the most prominent examples of pleiotropy involves dominant white. This gene, like lethal yellow, covers any other color that the animal would have. It is also inherited independently from the other white genes found in cats, which cause the tuxedo, van, and "cow cat" patters, among others. Dominant white causes an overall increase in the likelihood of the animal being deaf, but deafness is seen more often in individuals with at least one blue eye. With only one blue eye, the deafness is usually in the ear that is on the same side of the head as the blue eye. When both eyes are blue, it's highly likely that the cat will be deaf in both ears.

The white spotting genes (causing tuxedo, etc.) also can lead to deafness, but this is not seen as frequently as deafness in dominant white cats.

There are countless other instances of pleiotropy out there, some of which have not been confirmed through research. Correlation implies pleiotropy, and many genes correlate with secondary traits.

Sources are Genetics, North Dakota State UniversityPubMedUniversity of Tennessee at Knoxville, Genetics (second article)Berkeley, Louisiana State University, and MessyBeast. Images are from Wikimedia Commons with the exception of the photographs of my own mice and are under Creative Commons licenses: 1, 2.