Breeding for and Purchasing Better Dogs
The articles below are intended for the breeder and the general public. It helps breeders sort through there breeding programs to help guide them in a productive program and towards important goals. It helps the general public those who are in search of a breeder and who desire a dog of good health, temperament and character.
HOMOZYGOUS- when a dog carries two specific genes that are the same. (One is always passed on to the offspring)
HETEROZYGOUS- when a dog carries two specific genes that are not the same. This lessens the chance of passing on desirable traits.
PROGENY- the offspring of the animal.
PREPOTENCY- an animal that carries dominant genes in a homozygous form. (two of the same) and passes them onto thier offspring.
BLOODLINES- the genes that are carried in a specific individual. Bloodlines are produced over generations.
GENOTYPE- the true genetic makeup of a dog whether he visually shows them or not. (Example: he may carry a long leg and a short leg gene)
PHENOTYPE- what the visual genetic makeup of the dog appears to be. (Example: the dog has long legs)
LINE BREEDING- breeding back to a close relative to lock in specific traits creating a Prepotent animal for the purpose of improving the breed.
IN BREEDING- breeding very close relatives for generations in order to create a clone.
The Strategy of Breeding
Linebreeding, Inbreeding and Outcrossing
Inbreeding seems to scare the beejabbers out of some people. For those people who cannot destroy defective dogs, it should. For those serious breeders who can cull and carry on, it will eventually become an option. It is an extremely useful tool for diagnosing what genes are present. If the genes for bad eyes are present, but hidden or recessive, this will bring them out to their full extent. If there isn't any bad genes, then the puppies will be of very close uniformity and very able to reproduce themselves (theoretically).The resulting puppies will have a lot of genetic material that is the same as their parents and grandparents and will be close genetically to each other.
What is meant by inbreeding is this; breeding two dogs that are closer than cousins. Typically the
combinations are brother/sister, father/daughter, mother/son, and on the looser side, cousin to cousin, grandfather/granddaughter, half-brother and half-sister. You get the idea. The dogs should have or be common ancestors. People disagree about the exact point at which inbreeding becomes linebreeding but inbreeding is the quickest way to find out what poor genes are in the line and what dominant characteristics are in the line.
Genetically what inbreeding does for you is concentrate the traits in your stock, both good and bad and that is stressing good and bad. The bad is as important as the good. While you are fixing all those good traits in your population, a hidden trait may crop up that can wipe you out if you aren't careful. This is the down side of inbreeding. When those traits appear, the affected animal must be removed from the breeding program.
Inbreeding doesn't introduce new genes and does not eliminate bad genes that the line already has. It only shifts them around like a rubix cube. This often results in litters with high show potential, if the quality was high to begin with. It shows you what recessives you have lurking in the dogs' backgrounds, both good and bad. But there are drawbacks. Besides the possibility of bad recessives, inbreeding exclusively over time will eventually lead to infertility. It's like a Xerox machine. After so many copies, you have to renew the ink. The same with dogs, you have to introduce new genes. No reputable breeder will use inbreeding exclusively, and many breeders simply never use it.
Inbreeding increases homozygosis and decrease heterozygosis. Homozygosis means that certain traits will double up so that now matter what the dog is bred to it will carry on those specific traits. Heterozygosis means that more genes will be in a single dose and less likely to show up in any given trait. So inbreeding can duplicate both desirable and harmful genes, both of which can be unsuspected in the line, and may appear. Inbreeding does NOT create anomalies, it brings present anomalies to the surface. Even when the anomalies are present, inbreeding might not reveal them. However, once revealed, then the breeder can do something about them in the next generations of breeding. Usually, you will only find: very experienced breeders, ignorant breeders, and puppy mills making use of this technique.
Let's say that you've been inbreeding for a couple generations and you now have a genetic defect in your entire breeding population. Keep inbreeding, looking for those one or two clear animals and use them because they are almost exclusively clear of the problem. An increase in harmful recessives is undesirable but it is not a major drawback if they are identified early. The effect of inbreeding on major polygenic traits is greater. Generally, traits that are highly inherited or ones which are many genes added together to produce the defects, are not adversely affected by inbreeding but, traits under non-additive control, especially those tied to dominance and not of high heritability, are often markedly harmed by inbreeding.
Inbreeding is not for the faint of heart or those unwilling to keep their pups long enough to make
positive assessments. But for those who are breeding with a goal in mind, it gives them much greater
control over their gene pool and a direction to head towards knowing what exactly they are dealing with in their dogs.
This is probably the most common strategy in breeding purebred dogs (and in developing new breeds, for that matter). Through this method, new genes are slowly introduced and unwanted genes are slowly replaced. The actual rate varies by how strongly you line breed. It sacrifices little overall quality in terms of show quality. Usually the puppies are rather close in general conformation. The only problem with this method is that it often takes several generations to get poor genes out, (or adding desired genes in) resulting in many puppies that have the same genetic problems (or virtues) that their parents have. And then because some breeders are more interested in winning, they do not place the affected puppies on spay/neuter contracts. This is both a blessing and a curse for the breed. If the breeder is very careful, affected pups can be used wisely to prevent loss of quality, but still remove the affected genes by only breeding the affected pups to known non-carrier relatives. This way the breeder can again try to "edit out" the bad genes. This process results in dogs that will often reproduce their same level of quality. This is referred to as reaching homozygous litters (more genes of the same kind apparent in the puppies) and thus more uniformity.
Inbreeding and linebreeding really differ only in degree. Linebreeding is less likely to cause harm than inbreeding. Inbreeding is not for novices. Knowledge of genetics and the breed is required for success. For good results it must be well-planned and breeders must be ready for whatever problems it presents.
Outcrossing is generally used to introduce something new to a line -- a better head, better colors, better front, etc. Usually the puppies retained from these breedings are bred back into the breeder's original line to standardize them back into the line's general characteristics and reproducibility -- with the one desired characteristic. The tricky part is that other characteristics may come along for the ride!
If you are dedicated enough, you can eventually continue breeding by outcrossing alone (but don't expect instant or quick results). You should pick dogs that complement each other well and are similar in general appearance. This is a long hard road to eventually developing a line. Through outcrossing, many health problems can quickly be eliminated (or just as quickly added into your breeding), but usually you do sacrifice some show quality and producibility.
You have to remember that dogs that appear totally healthy may be carriers of genetic problems. To find this out, test mating is done to a dog that is affected with the genetic problem (resulting usually in puppies that are both affected and non-affected carriers) or by inbreeding to a related dog that also doesn't show the signs of being affected (usually littermates are used) this will usually result in some puppies free of the problem, some puppies as carriers, and some puppies affected. By breeding two dogs that carry the problem you may have to put all the puppies down).
There are variations on outcrossing. A "true" outcross could be a dog that has totally unrelated dogs bred together throughout the pedigree. This is very rare. On the other hand, "linecrossing" is a form of outcrossing where dogs from unrelated lines are bred to produce a new line. The sire and dam are usually very linebred from their prospective lines and the resulting puppies are varied in appearance, some looking like the sire's line and some looking like the dam's line and some looking like mixtures of both lines.
A strain or Line is a family of dogs with a set of traits chosen and developed by the breeder that will exclusively reproduce themselves by way of prepotency in the parents. Both parents will be homozygous for the particular traits that you have chosen and will reproduce the same way.
Improving your Stock - The In's and Out's
It's All In The GenesAs dog breeders, we engage in genetic "experiments" each time we plan a mating. The type of mating selected should coincide with your goals. To some breeders, determining which traits will appear in the offspring of a mating is like rolling the dice - a combination of luck and chance. For others, producing certain traits involves more skill than luck - the result of careful study and planning. As breeders, we must understand how we manipulate genes within our breeding stock to produce the kinds of dogs we want. We have to first understand dogs as a species, then dogs as genetic individuals.
When evaluating your breeding program, remember that most traits you're seeking cannot be changed, fixed or created in a single generation. The more information you can obtain on how certain traits have been transmitted by your dog's ancestors, the better you can prioritize your breeding goals. Tens of thousands of genes interact to produce a single dog. All genes are inherited in pairs, one pair from the father and one from the mother. If the pair of inherited genes from both parents is identical, the pair is called homozygous. If the genes in the pair are not alike, the pair is called heterozygous.
BREEDING BY PEDIGREE
To review some options,
Inbreeding significantly increases homozygosis, and therefore uniformity in litters. Inbreeding can increase the expression of both beneficial and detrimental recessive genes through pairing up. Inbreeding does not create undesirable genes, it simply increases the expression of those that are already present in a heterozygous state.
Linebreeding attempts to concentrate the genes of a specific ancestor or ancestors through their appearance multiple times in a pedigree. The ancestor should appear behind more than one offspring. It is better for linebred ancestors to appear on both the sire's and the dam's sides of the pedigree. That way their genes have a better chance of pairing back up in the resultant pups.
Outbreeding brings together two dogs less related than the average for the breed. This promotes more heterozygosis, and gene diversity within each dog by matching pairs of unrelated genes from different ancestors. Outbreeding can also mask the expression of recessive genes, and allow their propagation in the carrier state.
Geneticists' and breeders' definitions of inbreeding vary. A geneticist views inbreeding as a measurable number that goes up whenever there is a common ancestor between the sire's and dam's sides of the pedigree; a breeder considers inbreeding to be close inbreeding, such as father-to-daughter or brother-to-sister matings. A common ancestor, even in the eighth generation, will increase the measurable amount of inbreeding in the pedigree.
The Inbreeding Coefficient (or Wright's coefficient) is an estimate of the percentage of all the variable gene pairs that are homozygous due to inheritance from common ancestors. It is also the average chance that any single gene pair is homozygous due to inheritance from a common ancestor. In order to determine whether a particular mating is an outbreeding or inbreeding relative to your breed, you must determine the breed's average inbreeding coefficient. For the calculated inbreeding coefficient of a pedigree to be accurate, it must be based on several generations. Inbreeding in the fifth and later generations (background inbreeding) often has a profound effect on the genetic makeup of the offspring represented by the pedigree.
BREEDING BY APPEARANCE
Many breeders plan matings solely on the appearance of a dog and not on its pedigree or the relatedness of the prospective parents. This is called assortative mating. Breeders use positive assortative matings (like-to-like) to solidify traits, and negative assortative matings (like-to-unlike) when they wish to correct traits or bring in traits their breeding stock may lack.
Some dogs may share desirable characteristics, but they inherit them differently. This is especially true of polygenic traits, such as ear set, bite, or length of forearm. Breeding two dogs that visibly look or are (phenotypically) similar but (genotypically), the genes that the dog carries that you can not see visibly and are unrelated, bred together would not necessarily reproduce these visible traits. Conversely, each individual with the same pedigree will not necessarily look or breed alike.
Breedings should not be planned solely on the basis of the pedigree or appearance alone. Matings should be based on a combination of appearance and ancestry. If you are trying to solidify a certain trait - like topline - and it is one you can observe in the parents and the linebred ancestors of two related dogs, then you can be more confident that you will attain your goal.
Some breed clubs advocate codes of ethics that discourage linebreeding or inbreeding, as an attempt to increase breed genetic diversity. This position is based on a false premise. Inbreeding or linebreeding does not cause the loss of genes from a breed gene pool. It occurs through selection; the use and non-use of offspring. If some breeders linebreed to certain dogs that they favor, and others linebreed to other dogs that they favor, then breed-wide genetic diversity is maintained.
Dogs who are poor examples of the breed should not be used simply to maintain diversity. Related dogs with desirable qualities will maintain diversity, and improve the breed. Breeders should concentrate on selecting toward a breed standard, based on the ideal temperament, performance, and conformation, and should select against any detrimental breed related health issues. Using progeny and sibling-based information to select against both polygenic disorders and those without a known mode of inheritance will allow greater control.
There is no specific level or percentage of inbreeding that causes impaired health or vigor. It has been shown that some inbred strains of animals thrive generation after generation, while others fail to thrive. If there is no diversity meaning the gene pairs are pretty much the same in both parents and are non variable but the (homozygote) or genes that are present are not detrimental, there is no effect on breed health. The characteristics that make a breed reproduce true to its standard are based on non-variable gene pairs. A genetic health problem arises for a breed when a detrimental gene increases in frequency and homozygosity.
PUTTING IT ALL TOGETHER
Decisions to inbreed, linebreed or outbreed should be made based on the knowledge of an individual dog's traits and those of its ancestors. Inbreeding will quickly identify the good and bad recessive genes the parents share in the offspring. Unless you have prior knowledge of what the pups of milder linebreedings on the common ancestors were like, you may be exposing your puppies (and puppy buyers) to extraordinary risk of genetic defects. In your matings, the inbreeding coefficient should only increase because you are specifically linebreeding (increasing the percentage of blood) to selected ancestors.
Don't set too many goals in each generation, or your selective pressure for each goal will necessarily become weaker. Genetically complex or dominant traits should be addressed early in a long-range breeding plan, as they may take several generations to fix. Traits with major dominant genes become fixed more slowly. Desirable recessive traits can be fixed in one generation because individuals that show such characteristics are homozygous for the recessive genes and you will be able to see them. Dogs that breed true for numerous matings and generations should be preferentially selected for breeding stock. This makes them prepotent and of extreme value.
If you linebreed and are not happy with what you have produced, breeding to a less related line immediately creates an outbred line and brings in new traits. Repeated outbreeding to attempt to dilute detrimental recessive genes is not a desirable method of genetic disease control. Recessive genes cannot be diluted; they are either present or not. Outbreeding carriers multiplies and further spreads the defective gene(s) in the gene pool. If a dog is a known carrier or has high carrier risk through pedigree analysis, it can be retired from breeding, and replaced with one or two quality offspring. Those offspring should be bred, and replaced with quality offspring of their own, with the hope of losing the defective gene completely.
Trying to develop your breeding program scientifically can be an arduous, but rewarding, endeavor. By taking the time to understand the types of breeding schemes available, you can concentrate on your goals towards producing a better dog.
Information gathered from writings of Dr. Jerold Bell
Removing Defects So Which Is Best?
No simple answer will determine which breeding strategy is best. Whether you use Inbreeding, Linebreeding, Outcrossing or a combination of all three it all boils down to philosophy. Each strategy has favorable and adverse consequences. Using a combination of strategies and knowing how they drive selection and breeding in various portions of the population can help you choose among them, depending on the goals of your breeding program.
Inbreeding (and to a lesser extent linebreeding) makes for more consistent and more predictable animals, which can be good in some situations. It is useful if selection for vigor is going to be possible. Inbred populations have little variation, so that performance (temperament, conformation, color) can be accurately predicted. Inbreeding can also bring recessive defects to light. This too can be either good or bad. It is bad if selection is not going to remove (or at least identify) carriers from the population. It is good if the identification of carriers is going to act to reduce their frequency in the population.
With outbreeding, vigor goes up, especially reproductive vigor. Uniformity generally goes down, although one notable exception is the first cross between inbred or linebred animals that are from different tines. Crossing inbred lines usually generates very uniform animals, but these uniform animals do not in their own turn produce uniform offspring.
Outbreeding also tends to decrease (at least initially) the chance that rare recessive genes are brought to light. The good news is that many diseases are probably due to rare recessive genes, and therefore outbreeding is one way to avoid their expression. The bad news is that they will eventually show up in a population, for carriers eventually become common enough that outbreeding pairs them up and the diseases or deformities are expressed. In a deliberately outbred population the expression of defects can indicate that the genes responsible (for those defects that are genetic in origin) are widely dispersed throughout the entire population.
One good option is to breed for outbred females and linebred males. A single strategy to accomplish this is somewhat tricky but possible. In this system it is essential that the linebred males come from carefully documented lines, and that they are not carriers of any deleterious genes. Not just any male will do!
THE SURVIVAL OF THE FITTEST
This preservation of favourable individual differences and variations, and the destruction of those which are injurious, have been called Natural Selection, or the Survival of the Fittest. Man can act only on external and visible characters: Nature, is allowed to personify the natural preservation or survival of the fittest, cares nothing for appearances, except in so far as they are useful to any being. She can act on every internal organ, on every shade of constitutional difference, on the whole machinery of life. Man selects only for his own good: Nature only for that of the being which she tends.
Natural Selection Is the Key
Selection is the force that allows reproduction of some individuals and not others. It operates independently of any type of breeding system in animal populations. Selection is therefore a force for change in the overall genetic makeup of a population. Selection is a powerful tool, one that can irreversibly change a population.
Selection can involve any trait whatever: size, color, temperament and conformation. Selection can be intense and cause fairly rapid change over a few generations, or it can be more relaxed and change the population more slowly in the desired direction. Because selection can irreversibly change a population, the breeder needs to carefully consider his or her goals.
Selection can be responsible for changing the incidence of recessive genes. If a defect or disease is due to a recessive gene and the defect can be treated, then it is possible for the defective animals to reproduce. All offspring of these animals will carry the gene for the defect, whether or not they actually express it. This transmission, repeated in many individuals, can act to increase the frequency of genes for defects. Other alternative plans have different consequences.
Limiting reproduction of known carriers is important for the long-term genetic health of the population, although its practice will always be unpopular with owners of otherwise-outstanding individual breeding animals that happen to be carriers of genetic defects. The widespread use of carriers ensures that when these dogs are bred and carry on these unknown recessive genes, they will infect many many dogs in the population. The difficulty is that, if left unchecked, the genes can become so common in a population that selection becomes a difficult pill to swallow, because then a high number of individuals must be removed from reproduction. Some of the carriers are bound to be otherwise exceptional, and these are the animals for which the choices become very difficult.
Identification of carriers can come about in different ways. One way is to simply let individual breeding practices eventually bring carriers to light. This works reasonably well for defects of low incidence, since they are unlikely to overwhelm the population. The danger of this approach is that a single undetected carrier sire that is used widely can spread the defective gene far and wide before it is detected. Once these genes become common, reducing their incidence is a real headache.
In the case of more common or severe defects, it is possible to test for carriers more deliberately. One of the most powerful tests for genetic defects is the mating of parent to offspring. If anything weak is present it will be exposed. Unfortunately, the number of matings needed for this type of test is relatively high. To be 95 percent sure that the animal is not carrying deleterious recessives, it takes twenty-three normal offspring from daughters. To be 99 percent sure, it takes thirty-five normal offspring. Obviously, any abnormal offspring produced at any point along the way implicates the sire as having the genes for that defect. The logic works only if the defects are genetic.
If a carrier is detected, by whatever means, then the next step needs to be pondered carefully. If selection is aimed at decreasing the number of carriers, many different routes can be taken. One method is to neuter the affected individuals as they become known, the parents of the defective individual, and all of their previous offspring. This is the most radical selection against a defect, and it effectively removes carriers from the population as they are detected as well as some non-carriers simply because, based on the law of averages, they are more likely to be carriers by virtue of their relationship to known carriers. At very low gene frequencies carriers are unlikely to be detected because they are unlikely to be mated to another (equally rare) carrier. So while the "neuter all carriers" approach will work to dramatically reduce the number of carriers in a population, it rarely completely eliminates all carriers since some slip through the cracks of the system.
Other selection plans that work against carriers are better than nothing, but less drastic than neutering all carriers. One such plan is to neuter the sire because he can spread the gene more widely than can the dam, which produces fewer offspring. Still, half of the offspring of the carrier dam will be carriers. One approach to this problem is to neuter all of her sons but allow her daughters to reproduce. About half of these will be carriers. If these are in turn used for reproduction, the carrier rate goes down to about one-fourth, although which specific fourth is uncertain without a breeding test. If excellent males are generated, an alternative to this scheme would be to test-mate them to known carrier females to determine which of the males do not carry the defective gene. Those documented as free of the gene can then be used widely and safely for breeding of animals free of the specific defect. In this way, the positive traits of the line can be continued while leaving behind the defect. The process is long and involved but well worth the effort in some circumstances.
Modes of Inheritance
A dog is the product of its genotype, or the genes in its makeup, acting in a specific environment. Its phenotype is an expression of both the genotype and the environment, that of which you can visibly see.
Four modes of inheritance cause most genetic defects in dogs:
- Autosomal recessive or simple recessive
- Autosomal dominant
- Sex-linked recessive
An autosomal dominant trait results when a trait is expressed even though the pair of genes causing
the trait are not matched. Dominant traits are expressed in the heterozygous state, which means only
one parent must have a defective gene for the disorder to cause the trait to occur among the
Sex-linked genes can be either dominant or recessive and always appear on the X-chromosome,
making females carriers. The same distinctions between autosomal dominant and recessive traits also
apply to sex-linked traits. For example, the dominant gene hides the recessive gene in the female
since the female has two X chromosomes. In the male, with only one X chromosome, the single
recessive gene that is part of that chromosome expresses itself, causing the same trait that seems to
require two genes in the female.
Polygenic traits are controlled by a number of genes, each of which adds in increments to the total
phenotype. These are called complex traits because multiple genes are involved. Polygenic traits also
are called complex traits because environmental factors are also involved.
Protecting the Breed
In our quest for breed purity, the superior strain, and classic type, we have made a sad mess of our dogs - with unhappy, neurotic temperaments, epilepsy, blindness, deafness, immune system weakness, skin diseases, blood disorders, endocrine system malfunctions, crippling blood disorders, deliberate deformity, and often even the inability to reproduce their kind without breeder and veterinary intervention. How clever we have been!
The show ring has also been largely responsible for the decline of breed purpose, working ability and temperament in a great many breeds, notably sporting breeds, herding breeds and sleddog breeds. The quick and easy gratification of blue ribbons and gilt trophies all too readily replaces the hard work necessary to preserve and advance canine working abilities. If our dog breeds are to conform to the ideal of "a sound mind in a sound body" (as advocated by the proponents of the Advanced Registry), the fancy must find some way of ensuring that less dog-breeding takes place along the lines of least resistance and cheap gratification, so that greater attention is paid to working characteristics, temperament and trainability.
A balanced outlook on breed identity must be restored by integrating canine function with the ideals of conformation, beauty and "type." All kinds of dogs, toy breeds also included, can perform useful functions and respond to training. Those aspects of innate abilities should be given an importance at least fully equal to that of type and conformation instead of being regarded as merely optional. For example, breeding and exhibition of utility breeds such as gundogs, hunting dogs and sleddogs merely for sale as pets and for dog shows, with no effort made to maintain and advance their working capabilities, is an obvious abuse which must lead inevitably to mental and physical degeneracy in those breeds.
Those who attempt to set aside the balance arrived at by natural selection then struggle to attain and to maintain fitness in their stock. There is more to this than tired expressions about "soundness." Artificial selection alone, such as that used to produce winning exhibition dogs, involves breeding in a way which blatantly disregards most of the genetic makeup in the canine genome. Since genes assort in groups on chromosomes (a phenomenon known as "linkage"), inbreeding and selection for desired traits of superficial appearance unavoidably affect many other genes which are inadvertently selected and often fixed in a homozygous state in total ignorance of what is happening. This may be a major factor in the current prevalence of genetic diseases. Thus natural selection, when artificial selection is by passed, a high-level of nutrition, and advanced veterinary care is ignored, the breeder finds themselves with flawed genes and genetic unsoundness. It now reasserts it's self at a deeper and more serious level. So much now that healthy and hardy animals can no longer be produced, however they are typey and attractive to the eyes of the judges.
Declining vigor caused by accidentally fixing in sublethal and subvital genes will not be made up for by breed points and championships. Fitness and ability may not be replaced with impulsive aesthetic criteria. The animal's environment is the ultimate go between of its fitness and the environment will not be denied its say. You may vaccinate the dog and dose him with antibiotics, feed him with vitamins and minerals as you like, enclose him in a sterile pathogen-free laboratory environment if it comes to that! Still natural selection may not be avoided; it only emerges at a deeper level. In a sense the dog's environment includes his own physical body; if the genes which blueprint his physiology are flawed, then the dog is doomed regardless of his beauty and classic breed type. The truth is that the "superior strain" cannot be produced by manmade breeding programs and artificial selection; the breeder's decisions are subject to nature's veto at all times.
With what, then, will the breeder replace natural selection? If he replaces it with profit, the degeneration of his stock will in the end put him out of business because veterinary costs and death eat up his profit margin. If he replaces it with beauty contests, in the end his beautiful contest winners will only promote weaklings and degenerates. If he replaces it with screening programs for the "elimination of genetic defects," in the end his stock will succumb to inbreeding depression as bitches fail to whelp naturally and puppies die in the nest. If he replaces it with veterinary care, in the end his stock will die prematurely of incurable cancer, or the young will fall prey to viral diseases despite repeated vaccinations. If he replaces it with work and austerity, his stock may endure awhile longer, but in the end it will turn out to be afflicted with genetic ills that slipped through his demanding program, or its performance will mysteriously decline as the inbreeding coefficient creeps upward. In the end, natural selection cannot truly be replaced with artificial criteria. The breeder must find a way to work with natural selection, within the framework of what is now known about the biological operation of the natural world. We in the canine fancy must begin to take lessons from wildlife
biologists, from evolutionary biologists, from population geneticists.