What is a lethal white?

Question
I've been reading some of the questions and answers here and see the term lethal white. One expert said if you breed a boy pig to his mother she will produce lethal whites.  What is that?

Answer
Lethal White is a syndrome in certain Paint horses caused by a genetic mutation carried by the parents. The foal is born pure white, often has no rectum and the intestines are unable to work. They are generally blind, unable to eat or digest food and the outcome is fatal.

We refer to certain breedings of guinea pigs as lethal whites but it's not actually correct in the true genetic sense. It comes from the crossing of a Roan to Roan, Dalmatian to Dalmatian, or Roan to Dalmatian. It occurs with a fair amount of frequency although not every time.

These babies are pure white, have mutated dentition (bizarre shaped teeth) are often blind and most don't survive.  It's because of the gene carried by each parent the same as with horses. There are 13 different breeds of guinea pigs and 12 of them can have roan coloring. The exception is the White Crested which only has white on it's head.

The breeders of Roans and Dals claim they get their best results from breeding Roan to Roan and are willing to risk a lethal white in a litter. The babies that are born roans or dals and not pure white do not have these issues. However, they are carrying the gene.

Crossing a mother and son or father and daughter does not produce a lethal white. When creating a new breed or variety within a breed (variety refers to color and/or markings) these breedings are done routinely to concentrate or "set the genes" of the breed or variety you are trying to achieve.

Example: the color Tan(marked like a Doberman dog) was developed in the UK. A couple of breeders from the US acquired a few Tans and brought them here to be bred and accepted by ARBA, the governing body that determines what is and is not an acceptable color or breed able to be shown. It could be compared to the AKC here in the states. New breeds and varieties are made, not born.

The eight Tans that came her in the late 1990's were crossed with Golden Agoutis which have a red belly but the top is black with red ticking or tips. Tans have the red belly but are solid black on top. Each breeder took a baby from the litter, crossed it with the parent and the babies born then carried a gene from each parent.

That litter is then crossed back to a black pig. Some of the babies of that litter (each carrying stronger genes for the Tan than the agouti) were crossed back to that black parent. Another Tan is crossed back into that third litter and some but not all of those babies are born Tan, the rest still carrying the gene.

The entire process takes about six to eight years before the breeders are consistently getting Tans in every litter. There will still be a throw back agouti or black occasionally, but again even those babies are carrying the Tan gene. Again, crossing the baby back to the parent will bring out the desired colors.

Occasionally experienced breeders will cross a brother to sister for the purpose of exposing bad traits in a line. You either get the best of the best or the worst of the worst. If there are coat faults in the genetic line they will be exposed in this breeding. You do NOT get two headed, retarded babies. And it is not something that is done on a regular basis. The purpose is to define genetic issues, nothing else.

So to make a long story short, no you do not get lethal whites from crossing a baby with it's mother or father. It's done all the time. Having said that I must also add that this is not something that should be done routinely.  There is a genetic system to crossing what we call F1 and F2 generations.

It should also be noted that just because a pig is white does not make it a lethal white. The lethal is defined by the mutations, not just the color.

This is the same way that new breeds of dogs are created. It takes many years to develop them and is also one of the reasons that many purebred dogs have inherent health issues such as hip dysplasia, heart conditions, cancers, deafness, etc. Mutts NEVER have these issues because their gene pool is so varied that bad traits are not carried and expressed.

Interestingly enough, now that we have designer breeds like the Labradoodle, etc they too are carrying and passing traits because they're crossing them with their own breed (Labradoodle to Labradoodle, etc.)  The very things that are inherent in Labs are coming out in these designer dogs, all of them, not just this particular breed.

I'm sorry to be so windy about this but this is a subject that needs to be clearly defined so that wrong information is not passed on.