Форум » Breeding » Color genetics » Ответить

Color genetics

Nina: I think it would be very interesting to place Collies in the overall dog color genetics story. There were already some discussions on white dogs, so it should be a good subject to start. Sorry about my not-so-good English, I know I should probably find the original texts and paste them here... but this is shorter and easier... There are 3 basic ways the dog can be white: - Phaeomelanin dilution - Merle - Spotting Phaeomelanin dilution is said to be caused by the Chinchilla Allele. It turns red pigment (phaeomelanin) into light red, cream or pure white. Here's an example of how it works... Many white dogs - like Samoyed, Westie, Maltese etc... - are in fact genetically red dogs. Their eyes, eyelids and lips are always dark. They should not have trouble hearing, because (although they appear white) they don't lack pigmentation. This has nothing to do with Collies, so let's move on... Merle dilutes black pigment (eumelanin) randomly into silvery-blue with black splashes. A dog with one copy of that gene will have normal merled coat. With two copies, the result is some to most of the coat turning white due to the lack of pigment. Deafness or blindness can sometimes occur, but they can't be inherited separately from the lack of pigment caused by two merle genes. Normal heterozygous merle dog should never have any more health trouble than any other color. Merle was already heavily discussed here, so I believe this will be enough... Spotting is much less discussed, and in my opinion incredibly interesting. It is the gene that causes typical Collie white markings. It also appears in other breeds, in greater or lesser degree - Bernese, Basenji, Tornjak, Foxterrier, Bullterrier, Dalmatian, Dogo Argentino... White areas on these dogs contain no pigment... so theoretically, these white headed dogs have a chance to be blind or deaf.... however, that chance is not as big as in double merles, because spotting gene acts less randomly - it "takes care" of the important areas (eyes, ears...), making them least probable to lose pigment cells. This photo illustrates pigmentation pathway in a mouse embryo (same applies to dogs) photo courtesy of G. Barsh, Stanford http://homepage.usask.ca/~schmutz/pathway.html The melanocytes are migrating down from the neural crest derived cells along the spinal column and brain. Eyes and ears almost always have some pigment, and last places to recieve pigment cells are toes, chest, tip of tail, tip of nose... Spotting gene roughly determines when will this migration stop. For example in Dogo Argentino it stops almost immediately, leaving the whole dog white. In Labradors it goes all the way, leaving maybe a small spot on the chest or toes. Collies are somewhere in between. Besides the spotting gene, white markings are also influenced by external conditions. For example - if the mother has some sort of trauma in pregnancy that disrupted melanocyte migration, it can happen that puppies have more white markings than usual. That's why we can never predict exact amount of white markings some parents can give.

Ответов - 43, стр: 1 2 3 All

Alertness: Thanks Nina, that was an excellent, condensed introduction to the genetic reason for dogs being white or partially white! . Just to think that the pure white samoyed genetically is a red dog... Fascinating! As well as knowing why it's usually the toes and the tip of the tail etc which is spotted white. Berit

Nina: One more interesting fact... pigmentation spreading (mouse embryo picture) continues even after the puppy is born. Take a look at my smooth girl... ... notice how her white blaze narrowed with age. It's most apparent on her forehead, while the peripheral part (closer to her nose) changed very little. Her sister is even more interesting... She was born with lozenge - cute little sable spot in the middle of the white blaze. As she grows up, it merges with the rest and becomes almost impossible to detect. Notice that nose pigmentation closes some time after birth. It also has to do with pigmentation pathway.

Dianne: Thanks Nina - that explains a lot of things I have observed. For example, white factor - my girl Sadie is white factored. She has never had a white factored puppy. I was always careful to mate her with dogs who did not have too large a proportion of white in their markings. I don't know if I was just lucky or if scientifically what I did was right. For example, if I crossed two white factored dogs, would the offspring be white factored? Note that some of the early smooth collie champions were white factored to a very high degree. This seems to have been bred out in time, whether by choice or accident, perhaps we will never know. I haven't mastered the art of putting photos on the forum yet, but if no-one else does so in the meantime, will try to put an illustration in a later post. Dianne

Dianne: I've realised I don't need to put illustrations because, of course, thanks to the database, we have the Champions Gallery which is perhaps based on the Smooth Collie Club of Great Britain's 2002 book, smooth Collie Champions, 1884 to 2003.Which came first, the chicken or the egg, I am not sure. There have been extra dogs added to the Champion's Gallery. http://foxearthcollies.co.uk/champions_gallery/championsgallery_index.htm some white factored dogs to be found in the gallery are: 1898 Ithlingboro Village Boy 1902,Ithlingboro Village Lad 1907 Colet Lucy 1910 Stanley Wonder. There are a number of other possible whilte factored dogs, but not so easy to spot on black and white photos. An extra-long white mark on the end of the tail or white running up the hind legs, shoulders white with white running down the front legs are signs. Another interesting thing is that there were many more dogs with white blazes and noses (I personally think this is a pity this has disappeared to some extent because it is a distinguishing and attractive feature) and more dogs with little or no white collars. Dianne

Spiritwind: Here is a picture of one of my rough girls (VERY VERY VERY Out of coat) at about 18 months of age... Everyone thing she is white factored, buts he is not. She just fakes it really well. She has no white or white factored dogs in her pedigree and neither parent is white factored, however both her parents had full white collars. Now I LOVE large full white collars, and with the exception of a couple of my dogs, all of them have big full collars.... however I'm not a fan of blazes and while I've ever had a puppy with a full blaze, I doubt I would keep a puppy with one, if I got one in a litter.. however the little white star on their forehead I like.... or a tiny little stop of white on the end of the nose, I think is cute... I've gotten both on several puppies in the past.... jut not full blazes up the face.

Nina: I remember reading somewhere about plus & minus modifiers - polygenes that vary the degree of a characteristic roughly determined by some major gene. Little said there are 4 main genes at spotting locus (solid color, irish spotting, piebald, extreme white), but we can distinguish many more degrees. That's because other genes at other loci (we don't know exactly which ones) also impact spotting... some of them reduce it, while the others increase it. Merle gene is said to be an example of modifier for spotting - it supposedly increases the amount of white. I believe these modifiers + external conditions (like trauma in pregnancy) can explain Collies who look white factored, but in fact are not. I think today it's not so easy to find a real white factored Collie in European lines... like Dianne said, they're pretty much bred out. I must say I feel a little sad about that because I like them About blazes... I believe white markings on head and body are inherited separately. Take for example Bobtails - white heads on colored bodies. On the other hand white American Collies usually have colored heads and white bodies. I tried to search some texts on white heads, but never found anything specific about the way of inheritance... I somehow doubt we can accurately predict blazes... maybe roughly, but seems like surprises are always possible. If someone knows more, it would be great to read...

Alertness: I must disagree with you that white factored collies have been bred out of today's population. Maybe it is to some extent in many lines in the rough population, but not in the smooths. I see quite a lot of smooths who are white factored. Or they might not look it themselves but they give white factored pups . A much used and popular winning line from Sweden (used by most breeders in Europe) have the white factor present in its line. Also a full collar is a common accessory among smooths, but not among roughs, so generally I see much more white on the smooths than the roughs I see in the show ring. I remember something a Swedish breeder of roughs said (she is world renown for her beautiful roughs) and she is not afraid of using white factored dogs in her breeding. She does it knowingly because she wants the big, full white collars. Of course she sometimes gets a puppy that has too much white, but that's a small price to pay . Not all puppies in a litter are show prospects anyway. So not all breeders in Europe think the white factor is a dangerous liaison Berit

Nina: So not all breeders in Europe think the white factor is a dangerous liaison Glad to read this I just wanted to say it's very difficult to determine a dog's actual genotype judging by its appearance... especially in the case of spotting, where many different modifiers can impact the final result. It would be interesting to hear if anyone got a white pup (spotting white, not white merle) from European lines?

Spiritwind: however you can still get full white collars, and white front legs etc... the "flash" white markings on a collie, without having a dog that is white factored..... I do not have white factored dogs, but with the exception of 2 of my dogs, all of the others (rough and smooth) and large full white collars, white legs etc..etc..etc.. and I do not have any white factored dogs. The dog in the photo above I posted (Kelsey - rough tri) her mother and father both had full white collars... her sister (a smooth sable) as a full white collar.... and Kelsey's daughter (a rough sable) as a large full white collar... as does her granddaughter (also a rough sable).... large full white collars, with white front legs... Color headed whites and/or white factored dogs have no health issues related to their color, however I am just not a fan of the family of dogs in the US that the white/white factored dogs come down from.... My dogs pedigrees are Parader based... if you go back far enough in the pedigrees....

Alertness: I know the full white collar is not directly linked to the white factor, but at least in Europe it seems the less white factored dogs you use the less full collars you see. Maybe it's just because some breeders alltogether avoid using collies with much white on them just to be on the safe side (as many are afraid of the white factor; beats me). Anyway, it is true that most smooths in Europe have the full white collars whereas it's not as common in the roughs. Berit

Spiritwind: Oh I understand what you are saying..... A friend of mine who used to breed Collies, actually I purchased my foundation bitch from her several years ago. She had MANY MANY collies with almost no white collars what so ever... barely any white on their chest, just a small spot. She liked this.... my dogs are closely related to hers, as I said, I purchased my foundation bitch from her.... however my bitch had a big full white collar.. and I have maintained that with my own dogs, as I prefer the flashy white markings. This is Hershey, one of the dogs bred by my friend... several years ago. This is the kind of markings most of her dogs had.. not all, but most. Her sire was a sable, that also had these same markings. However this was my foundation bitch, Angie... who is CLOSELY related to Hershey, but thankfully has a huge full white color... Angie is pictured at 14 months of age. Angie is behind every dog I currently own.... I have her kids, grand kids, and Great Grand kids here now... she is Kelsey's dam (tri pictured above)... and they all have large full white collars like Angie!..

marakoopa: Nina wrote: It would be interesting to hear if anyone got a white pup (spotting white, not white merle) from European lines? We have had a white puppy in our second litter. Her parents are Whashishi's Fjurdy-Flora x Zap and it's done Fantazija. Tri x BM This is a picture of her: http://www.marakoopa.nl/foto/nestB/Baringa/2008-07-12%20Kyra%20rechts%20staan%20(1).jpg Thats why this is a very interresting subjet for me. No one can really tell me how it is that she is white. Janet I'm sorry, but can't get the picture right. But you can see her on our site: http://www.marakoopa.nl/baringa.html

Spiritwind: Do you have pictures of her parents?? This is very interesting because she really does not look like a white (color headed white) based on the markings on her head, she looks almost more like a double dilute. Was she the only one in her litter like this? If she is in fact a regular color headed white... then both her parents were obviously white factored whether they looked it or not. She is a very interesting dog though... and very pretty! I like her! Another possibility is she being a Harlequin blue merle. I'll try to find some pictures, but in the states we have some bloodlines in blue merles, where they carry the harlequin merle gene and sometimes the blues are SOOO light in color, they almost look white.... with large black patches... sort of like harlequin danes.

Spiritwind: Here are 3 pictures of Harlequin Blue Merles. They are NOT whites, none of their parents are white factored, there are several lines in the US that produce blue merles like this. These dogs are also NOT from two blue merle parents. When bred to a tri they will produce regular blue merles, harlequin blue merles and tris.. These dogs are owned/bred by different breeders I know... I have a blue merle girl that is similar to the one in the last picture, as far as color goes.

Natalain: marakoopa It`s interesting! Is this dog has no problem with vision or hearing? She looks more like white from bm * bm parents. I know 2 cases of latent blue merle colour (in rough collies). In both cases dogs looked like usual tricolour, but genetically they were blue merle.

marakoopa: Spiritwind wrote: Do you have pictures of her parents?? Was she the only one in her litter like this? Her mother: http://www.marakoopa.nl/fjurdy.html Her vader: http://members.chello.nl/c.berkelmans1/zap/index2.htm She was the only one in our litter. http://www.marakoopa.nl/B%20nest.html I had never heard of a harlequin blue-merle before. I don't know if she is a harlequin. She doesn't really look like the pictures of the harlequin.

Mabinogion: that was olso the first thing i was thinking ,that she look like a double dilute dog,mother is coming from a blue merle mother ,so it is possibel that there was a tiny small spot of merle ,but you can not know that now. but that is just guessing! we had two litters from this blue merle male who is the father of Marakoopa's bith and we have not much white in the litters.

marakoopa: Natalain wrote: Is this dog has no problem with vision or hearing? She looks more like white from bm * bm parents. No problem at all. Her vision and hearing are good. If her mother is a latent blue merle that looks like a tri-colour, then we sould of had problems with her first litter. She was mated to a sable dog and then we also would of had sable-merle. This is not the case. So I don't believe that Fjurdy is a latent BM. Janet

Natalain: marakoopa I`m glad that she havn`t problems with vision and hearing! It`s good! But... Really interesting why she is white... I understand that you don`t believe that Fjurdy is a latent BM. But.. I have seen in your homepage that her 1st litter consisted from 4 puppies, 3 tricolour and one sable isn`t it? Statistically it is not enough for be sure, I think. IF Fjurdy was my brood bitch I will mate her next time with tricolour male and see the results...

Spiritwind: marakoopa wrote: Her mother: http://www.marakoopa.nl/fjurdy.html Her vader: http://members.chello.nl/c.berkelmans1/zap/index2.htm She was the only one in our litter. http://www.marakoopa.nl/B%20nest.html Very interesting because neither of her parents look white factored. It is possible that they are, but just don't look it! Very interesting! But the puppy really doesn't look like a color headed white either, with all that white on her head, MOST color headed whites don't have that much white on their heads. She really does look more like a double dilute/double merle and I still think harlequin could be possible... though it doesn't sound likely. marakoopa wrote: If her mother is a latent blue merle that looks like a tri-colour, then we sould of had problems with her first litter. She was mated to a sable dog and then we also would of had sable-merle. This is not the case. So I don't believe that Fjurdy is a latent BM. Not a guarantee. I know people who have bred blue merle x blue merle and not had ONE problem with any of the puppies. Also as far as sable merles, I have done three sable x blue merle breedings and I have only ever gotten 1 sable merle puppy. I don't know if they have the DNA tests in Europe, but in the US and Canada they do have DNA tests to determine the genetic color of a Collie. It would be interesting to have this puppy DNA tested to find out what color she is genetically!



полная версия страницы