Mary Allen
One of the most popular breeds of rabbits is the pintos: prickly or lop-eared, in all sizes, colors, and patterns. In the third part of the painting series, we look at the genetics behind the spotted animals.
Whether with a few large or many fine spots, whether piebald or Dalmatian pattern: piebald rabbits are a feast for the eyes and attract admiring glances at exhibitions. The piebald is one of the few dominant mutations next to iron-gray and, like these, is split. Despite their different patterns, coat piebald and spotted piebald are at first glance genetically the same; the genetic abbreviation for the split type piebald is Kk. So a black piebald would be ABCDgKk, a blue piebald ABCdgKk, a Madagascar piebald AbCDgKk.
Homogeneous KK piebalds are less strongly colored than the KK type piebalds; they are called mustaches because of their head markings, other names are white lines or chaplains. This homozygous form is often associated with an intestinal problem, the megacolon, the severity of which varies. In addition to animals that do not reach adulthood, there are animals with normal vitality that can even be used for breeding. This is a stroke of luck for the breeder because when mating a mustache with a full-colored animal, he gets 100 percent spotted type.
The piebald pattern is extremely variable: the classic piebald with a few large side dots, dorsal stripe, colored ears, eye-ring, and cheek spot can be found in the dwarf and giant piebalds and in the Czech piebalds. The English pintos have a finely dotted lateral drawing in the form of a cornucopia. In the case of the Dalmatian piebald, large spots should be distributed over the body, the dorsal line and butterfly are resolved.
The coat piebald also carries the gene variant Kk. As the name suggests, the markings cover the body like a coat, only white on the chest, shoulder patches, and a small patch on the forehead is required. Three-colored spotted piebalds also need the mosaic factor bj to separate yellow and dark colors. The gene formula of the three-color piebald is, therefore: AbjCDgKk.
Hotot and White-Eared Unique
The full-colored animal’s kk, which fall in the piebald breed, are genetically interesting because they carry information about the type of piebald: A full-colored mantle piebald, for example, paired with a standard mantle piebald, in turn, inherits the mantle markings. Accordingly, English piebald times fully colored English piebald always clearly shows the fine piebald in the form of the cornucopia. But what happens when a solid English piebald is crossed with a mantled piebald? Here both patterns suddenly appear in the young animals: finely spotted in the English way or with the mantle pattern.
The gene K or k decides on piebald (KK or Kk) or non-piebald (kk). However, what exactly the spotting looks like is regulated by so-called modification genes (see box). With the help of these, the ultimate breed of piebald, the Hotot rabbit, may have emerged, in which the black color has been replaced by the white piebald color down to the thin eye-ring.
After the first unsuccessful attempts at the crossing, the French Baroness Eugénie Bernhard concentrated on piebald rabbits and selected their offspring after fewer and fewer markings, until – after 500 litters – only the eye-ring remained. Like any other pinto breed, the Hotot is split. Another theory is that Hotot is a combination of spotted piebald and plate piebald, but the origin story contradicts this theory.
A unique feature of the rabbit world is the white-eared rabbits, which are not recognized as a breed but are quite popular in hobby breeders. It is likely to be another mutation of the piebald gene K and is referred to as Kwo. The starting point was a medium-sized landrace from the Westphalia area, but the white-eared pattern has meanwhile been crossed into other breeds.
The pattern is inherited dominantly like the spotted piebald and only shows the typical pattern with white ears, white snout (“milk mouth”), white chest, and white legs in the split form Kwok. The ears can sometimes show minimal color residue. Homozygous white-eared KwoKwo is almost white and crossed with single-colored animals resulting in 100 percent white-eared dogs. In contrast to the mustache, homozygous white-eared dogs do not show reduced vitality.
Plate Check of the Dutch
Dutch rabbits are also spotted, but genetically their markings have nothing in common with spotted piebalds. Dutch rabbits are not split, the pattern is inherited as a recessive mutation ss. However, the theory of simple recessive inheritance has clear weaknesses: crosses between single-colored animals and Dutchmen already show small white markings on the nose and paws in F1. This should not occur with recessive inheritance. Rule 1 of Mendel (uniformity rule) states that the F1 generation must be uniform and show the phenotype of the dominant genetic part (see «Animal World» No. 1 / 2020).
The observation that the plate piebald covers a huge range from fully colored animals with small white markings to almost pure white rabbits led to the theory of the accumulating Dutch factors (s1, s2, s3…), which lead to animals with more and more white as the number increases. Standard Dutch is symbolized with s2s2.
Dutch coloring is not the only rabbit color that relies on accumulating modification genes. The intense red color of rabbits, Deilenaar and Sachsengold, and the large family of silver rabbits also have their origins in quantity genes. More of that in the next episode.