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Inbred Linebred and Outcrossed

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74 – September, 2014

by William Given

Inbreeding, linebreeding and outcrossing are terms describing the three methods for blending canine bloodlines to achieve a desired consistency of genotype and phenotype. Used wisely, they provide enlightened breeders with an array of valuable systems to aid you in determining the direction and control of a well-planned breeding program. Each plays a vital role in meeting the needs of the small breeder. And, in the larger scope, of the preservation and maintenance of the breed and it’s most desired characteristics. Defined briefly:

Inbreeding is the breeding of two dogs that are very closely related to one another, a sister to a brother, sire to a daughter, dam to a son, and in some cases the mating of half-siblings or of aunts and uncles with nephews and nieces. Because inbreeding amplifies the genes for weaknesses as well as those for strengths, inbreeding can be either highly successful or a dismal failure. Its use thus necessitates the ability to accept the disappointments that are mathematically certain to occur and the willingness to cull frequently and even heartlessly to make certain that those failures are not repeated.

Linebreeding is a much more conservative form of inbreeding. It usually involves the breeding of more distant relatives in the interest of concentrating the genetic code of a specific stud dog and brood bitch, thereby intensifying the probability of developing prepotentcy for many of the superior traits of the two dogs. The more often the bitch’s or stud dog’s name appears on the pedigree, and the closer to the front it is, the more tight the linebreeding has become.

Outcrossing, as you might expect, is the mating of two dogs that are not related to one another. It is also a term used for breeding away from certain families and bloodlines that have become too tightly bred and need an infusion of “outside blood.” Outcrossing is generally used to reestablish overall health and fertility that might have been lost through inbreeding or extended linebreedings.

Basic Genetics

On the simplest level, genes are bits of DNA molecules that cause certain proteins to be created within a cell and dictate every heritable trait (traits that are passed on rather than those that are impacted by environmental factors) that make a dog all that he is. Genetic information is carried in the cell nucleus by chromosomes. Diverse compositions of genes control everything from color and length of coat, to conformation and overall well-being, and to intelligence and temperament. Genes carry pairs of alleles that modify their given traits to a lesser or greater extent. When paired, these alleles are said to be dominant if the traits they express override other traits found on their corresponding allele. They are said to be recessive if these traits are unexpressed due to the presence of other overriding dominant alleles.

A gene is said to be homozygous if the paired alleles are both dominant, in which case the dog will always pass on a dominant allele to its offspring, and the offspring will always show that dominant trait. It is said to be heterozygous if its paired alleles contain one dominant and one recessive component. In this case, the dominant allele will be the one that is expressed, but the recessive allele is still present, and could be passed on to the offspring.

Each parent of a dog contributes 50 percent of its genetic material to each one of its offspring. And, 25 percent of which material was received from each of its parents in turn. Say you are breeding two dogs that have nothing in common. Depending on what 50 percent of genetic code was contributed from the sire and dam, all of the offspring of this particular mating could conceivably look quite different. If this is the case, the good news is that no major weaknesses are turning up. Weak breed characteristics are very frequently recessive traits and are thus unexpressed unless concentrated in a manner that makes them homozygous. Therefore, your puppies should be relatively free of congenital health concerns, and should achieve (at a minimum) average conformation, overall health and well-being, and fertility of their breed. The bad news is that the lack of dominance for certain traits that you think are important may be keeping you from getting the consistently good quality puppies you really want. This is a classic outcrossing dilemma. The results are safe, but not necessarily spectacular.

Selecting For a Desired Trait

Here is how the theory works in practice. Say your bitch has a grandsire that you particularly appreciate because of a certain set of traits that he passed on to many of his get with great regularity, (We will use the stud dog for our example, but it could just as easily be the brood bitch). Maybe he possessed an incredibly nice head and rock solid topline, or had great reach and drive, or a remarkable temperament. Maybe he had a combination of these desired breed characteristics. His granddaughter, if you have been lucky in your choice of bitches, might have inherited some of these qualities from him, but she would not have gotten more than 25 percent of his genetic material, and that will have been altered in some way by the presence of the other 75 percent of the genes that she has inherited from other ancestors. If you breed her to an unrelated dog, the contributions of her superlative grandsire will become even further diluted, until the qualities you wished for from that individual become all but negligible.

To ensure that the inheritance of that lovely bitch will be passed on with increased probability, you may choose to breed to another son or grandson of his that expresses his same strengths to a large degree. You might even go back so far as to flirt with inbreeding, and breed your bitch back to her grandsire or an equally handsome full brother of his. The goal of the mating is that the resulting offspring will have a greater concentration of the desired genetic material, and thus a greater likelihood of possessing the same superior breed characteristics. This concentration of genetic material also results in a higher incidence of homozygosity for certain heritable traits, and thus may actually become dominant for them. If this occurs, the puppies that result from the breeding may have a prepotency for those desirable traits. If that is the case, it means that he or she will tend to pass them on to subsequent offspring with a great deal of consistency due to the dominance of the alleles concerned. If you have been in sport long enough, you have had to hear breeders talk about a dog that “stamps his get” (or “her produce”), this is what they mean.

By now, you may well be wondering, if inbreeding and line-breeding have the result of creating superior show dogs by intensifying all that great genetic code, why are we not doing it all the time? Well, there are, of course, several reasons. The single greatest reason is that when certain genetic information is being combined in a highly concentrated manner, it also magnifies whatever weaknesses have been masked by the dominate genes even in an outcrossed milieu. Back to our example, although the grandsire possessed many absolutely outstanding qualities, he also had very bad feet. Perhaps bad feet are almost unknown in your breed, so this aberration went all but unnoticed as long as the stud dog in question was bred to bitches whose feet were at least as good as the breed average. The bad feet in this case remain recessive, masked by the breed’s dominant genetic inclination toward good feet.

When you start experimenting with inbreeding and linebreeding, whatever genetic combination occurred to give the grandsire dog bad feet will be made stronger by the concentration of that trait. It is thus possible that when you breed your bitch to a related stud dog, and both have decent feet, and you may not even be aware of the “bad feet problem” that existed in the grandsire, you may be shocked when you are presented with a litter of puppies that typifies everything you wished for, except for having terrible feet. A large breeder with time and money to spare may look at this situation as a learning experience, cull the litter from his or her breeding program, and breed the bitch back in hopes of getting a litter of puppies with better feet. If the second attempt succeeds, and it could, the pick puppy can be kept for the future and the other puppies may be placed in good show or pet homes. The unexpressed tendency to bad feet will remain recessive unless a future breeding with another dog with the same genetic concentration brings it out again.

However, a small breeder will not have the luxury of trying that breeding a second time and culling the less-than-perfect puppies, and may feel forced to keep one or two puppies as show prospects despite their feet. In this case, the genetic code for bad feet will be passed on yet again, perhaps now as a dominant trait. And so, the unweary breeder has unintentionally loosed a heritable defect into the gene pool of a breed that before this time had not been known for bad feet except in very rare instances.

The Shrinking Gene Pool

The other drawback of consistent inbreeding and linebreeding is that, over time, if you continue to breed close relatives through a number of generations, it decreases the gene pool to the extent that many good qualities will be lost in the shuffle. By definition, inbreeding reduces the numbers of gene pairs that can be inherited by any offspring, which is why inbred dogs have such a high prepotency for certain traits. The process of inbreeding has simply eliminated a wide variety of alleles from the genetic code of those dogs. It is thus quite true that inbred systems, over time, will suffer from a general loss of size, fertility and vigor. These things are improved by heterosity (the presence of a large variety of genes). The more inbred a dog is, the more homozygous its genotype, and the less access is available to traits that are dependent on a variety of alleles for their expression.

This loss of vigor, and the resulting genetic weaknesses that occur with it, are not solely created by inbreeding. These can be traits that may have existed in a recessive state and have been expressed due to the consistency of their concentration by breeding back into the line of dogs that carry them. Or it may just as easily be that traits that include vigor, fertility and freedom from genetic weaknesses rely on heterosity to be expressed and maintained in a healthy state.

The Right Balance

Inbreeding and linebreeding should always go hand in hand with judicious outcrossing to ensure the continued overall health, fertility, intelligence and temperament of your dogs. Inbreeding and linebreeding can certainly produce the spectacular individuals that you have long dreamed of, but Mother Nature has proven over and over again that the greatest “meshes” (breeding that consistently produce outstanding specimens) are often those that occur between two unrelated (though possibly linebred within themselves) individuals whose genes combined to produce what is commonly referred to as hybrid vigor.

Geneticists readily admit that they are not quite sure why it is that hybrid vigor works, but there is no arguing with the fact that in certain circumstances the breeding of two unrelated lines will result in the genesis of a litter of dogs that are far superior to their parents. This is especially true in the context of traits that are controlled by a number of different genes, rather than those that are expressed very specifically. Two examples of the latter would include working ability and intelligence. The former consists of a variety of alleles controlling traits such as conformation and movement. Size, which is genetically programmed, can be affected strongly by environmental factors such as the lack of proper nutrition. Bone is generally considered to be moderately heritable, and along with substance seems to rely in part on its genetic dominance in certain breeds or bloodlines. Thus it is that increased heterosity, or the exposure through breeding to a broader array of genetic material, increases the chances of a given dog inheriting the combination of genetic code that will result in superior show dogs.

The Magic Mesh

If the genetic code passed on by your dog has an affinity for that of its mate (more correctly put, if the alleles concerned combine in a way that produces dominance in certain important respects while masking any recessive traits that would be undesirable), then you have the puppy of your dreams, and not just once but repeatedly. The discovery of these nicks is, of course, 75 percent pedigree research and hard work, 20 percent intuition and five percent sheer dumb luck. Even geneticists freely admit that luck, chance and happenstance play a major role in the final genetic inheritance of full brothers and sisters. For this reason, you are likely, in a single litter of dogs, to get one superstar, a couple of above average performers, one or two strictly average, and a sire and dam both worth their weight in pure gold.

Unfortunately, the top ranked dogs of today may not even pass their outstanding qualities on to the next generation with anywhere near the consistency of their parents. The variety of combined attributes that has made them great can combine with the next generation’s breedings in ways that are varied and erratic. It depends greatly on the genetic code added by the brood bitch and the selected stud dog. And so, the cycle begins again. The question of whether to linebreed and how much, or of whether to inbreed and to whom, when to outcross and which lines will provide the needed “punch” to create the next generation of superstars. Again, it is your knowledge and intuition that will increase your chances of succeeding.

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Posted by on Sep 9 2014. Filed under Current Articles, Featured. You can follow any responses to this entry through the RSS 2.0. Both comments and pings are currently closed.

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