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Genetic modification and Incest

  1. Nov 3, 2012 #1
    What really happens with genes during incest? From what I understand there is a genetic pool of species and let's say there's a feature in some family like retracted jaw and if those people just keep breeding within themselves that jaw will be more and more retracted but if they go and breed with someone that's not family then that jaw will be going back to normal (average) of the jaw size of that genetic pool. So from my understanding it's like magnifying digital picture from let's say 100 pixels to 1000 pixels: same pixels start to copy themselves and you have blurry picture.

    But let's say hypothetically if there was just few people on some place could they genetically manipulate their genomes by going into genetic base and extracting some other genetic code to make "uninbred" offspring? Because let's face it human has many relatives and many people in his genetic past that made him. Like for instance very close relatives like brother and sister could they somehow reach and manipulate their DNA or chromosomes in a way to create "uninbred" offspring? Or for instance small group of people that are not related and will not have access to genetic pool manipulate their genes or chromosomes somehow to make their descendants free of one way inbreeding situations?
    Last edited by a moderator: Nov 3, 2012
  2. jcsd
  3. Nov 3, 2012 #2
    The scientific word for what you are talking about is “inbreeding”. Incest is a value laden word that refers more to cultural laws that restrict breeding. Human cultures have developed incest laws that have nothing to do with genetics. Conversely, lots of mating that is permitted in human culture has effects on genetics.

    I am not sure what exactly you are asking, but let me conjecture. You seem to be claiming that beyond the first generation effects caused by recessive genes, the effect of inbreeding is solely conservative. The effect of inbreeding is to slow down the accumulation of genes by natural selection. Any effect caused by excessive inbreeding can be reversed. This is not true.

    The first effect of repeated inbreeding is Mendelian segregation. This is random in most senses of the word, and would occur even without selection (natural or artificial). The different lineages split up into lineages that are homozygous for each allele. Since the lineages are homozygous, recessive genes are forced to express themselves in almost all cases. However, some recent studies indicate that Mendelian segregation is not inevitable in an inbred population. See the links below.

    Mendelian segregation is slowed down by chromosomes because the genes in a particular chromosome stick together. Alleles switch out of a chromosome only because of the occasional cross over or translocation during meiosis. Therefore, not all alleles sticking on the same chromosome will be homozygous. However, cross over speeds up Mendelian segregation because in the long run, no gene remains stuck to its chromosome.

    The effects of selection are amplified by Mendelian segregation. This is not random in the sense that a mutation is random. After effectively all the lineages have become homozygous for everything, all the alleles are force to express themselves whether or not they are recessive. Thus, a genetic variation can’t “hide”. Thus, evolution would speed up.

    Inbreeding could become really important after a mass extinction. If there are only a few survivors of a particular species, extreme inbreeding is unavoidable. Mendelian segregation would occur after only a few generations. The natural selection on the different lineages would be maximized. However, that is only my conjecture.

    There is a common belief among nonscientists that inbreeding causes an orderly process of “degeneration”. Inbreeding does not cause “degeneration” in the sense of an orderly program of getting worse. By forcing recessive genes to express themselves, it can actually eliminate the accumulation of recessive genes that do bad things. However, the combination of extreme inbreeding and random mutation is very much like asexual reproduction. Any bad mutation in a lineage stays for as long as that lineage survives. If enough lethal genes accumulate, the lineage is terminated. So in the sense of long term survival, extreme inbreeding is bad.

    Here are some links concerning “inbreeding” and “Mendelian segregation.”

    http://www.eplantscience.com/botanical_biotechnology_biology_chemistry/genetics/inbreeding_depression_and_heterosis/genetic_basis_of_inbreeding_depression_and_heterosis.php [Broken]
    “Some lines receive more favourable genes than others, accounting for differences observed in the degree of inbreeding depression in different lines. Thus, it is quite clear that the inbreeding depression is not a process of degeneration but a consequence of Mendelian segregation.”

    “Mendelian Segregation and Chromosomes
    “It is obvious from the beginning, however, that all the factors carried by the same chromosome should tend to remain together. Therefore, since the number of inherited pairs may be large compared to the number of chromosomes, we should find not only independent behavior of pairs, but also cases in which characters are linked together by their inheritance.”

    The precise 1:1 segregation of Mendelian heredity is ordinarily taken for granted, yet here are numerous examples of ‘cheating’ genes that perpetuate themselves in the population by biasing the Mendelian process in their favor. One example is the Segregation Distortion system of Drosophila melanogaster, in which the distorting gene causes its homologous chromosome to produce a nonfunctional sperm. This system depends on three closely linked components, whose molecular basis is beginning to be understood.”

    Recent studies show that some genes counter Mendelian segregation very nicely, despite what previous researchers thought. For these genes, segreagation can have long term consequences in evolution.
    “On the Evolutionary Stability of Mendelian Segregation
    “The expected outcome of the evolution of sex-specific segregation distorters is all-and-none segregation schemes in which one allele at the primary locus undergoes complete drive in spermatogenesis and the other allele undergoes complete drive in oogenesis. All-and-none segregation results in a population in which all individuals are maximally fit

    Early Effect of Inbreeding as Revealed by Microsatellite Analyses
    on Ostrea edulis Larvae
    This paper reports new experimental evidence on the effect of inbreeding on growth and survival in the early developmental phase of a marine bivalve, the flat oyster Ostrea edulis… These results suggest that microsatellite markers, often assumed to be neutral, cosegregated with fitness-associated genes, the number of which is estimated
    to be between 15 and 38 in the whole genome, and that there is a potentially high genetic load in Ostrea edulis genome. This load provides a genetic basis for heterosis in marine bivalves.”

    Sure they could. However, this is just a form of artificial selection. Selection of any kind can defeat "Mendelian segregation."
    One could do the same thing without the high tech. Use low tech breeding. Just go "flush". Keep having babies at a high rate. Kull (kill or sterilize) any defective individuals. The bad genes would be eliminated. Then, the natural mutations will force the population to have a high degree of genetic variation. The effect will be to have a population that is effectively outbred.
    I think this is basically cladogenesis. Evolution tends to cause populations to branch out into many species. This is basically the process. All species are basically inbred populations. It just that they reproduce so rapidly, the mutation rate beats the the Mendelian segregation.
    Last edited by a moderator: May 6, 2017
  4. Nov 13, 2012 #3
    Pediatricians who are geneticists deal with this a lot. The fact is that even if the technology to uninbreed genes is available the current approach is to focus on the genes that are lethal or those with lifelong morbidity. There is no screening protocol to go after every single gene that could be a problem. It would be extremely expensive and not helpful in the long run.

    And there is still no way to know if there are genes not discovered yet that could be detrimental.
  5. Dec 2, 2012 #4
    Ok thanks for the answers. I've been thinking about it and from what I gather gene is a part of DNA which is in every cell and it holds writing from which it tells cells and so organs how to function. Therefore genes are not so much of a problem because they're just a writing. So we're talking about chromosomes here.
    And to cut the story short if we had a small amount of beings of a certain species where inbreeding is inevitable and deadly would it help if during fertilization when chromosomes are being paired someone would interfere in those 23 pairs and if you can imagine karyotype took for instance one chromosome from pair 3 and removed one chromosome from it and replaced it with a same type chromosome of an outside person then of that couple; and then let's say replaced chromosome "y" that comes from "dad" and put "y" of some other man and so on.
    Because from what I know retardations and stuff like sterility come from to much or too little chromosomes in a certain pair. Like if you have xxy chromosomes togehter instead of normal xy. So is it mostly watching how chromosomes will pair?

    And also when it comes to pedigree dog species that is suffering from inbreeding is it suffering just because close inbreeding or mostly because people choose bad features like short noses in some species or shorter hind legs in other...
  6. Dec 2, 2012 #5
    The answer is "yes".

    Inbred dogs have both types of problems. First, certain recessive features that no breeder would select are expressed due to inbreeding. Second, generations of inbreeding can result in certain features purposely selected for being amplified to the level of lethality.

    No breeder would ever chose for diabetes, hip diplasia, hemophilia or lack of resistance to infection. Yet, inbreeding can cause these diseases by forcing the alleles associated with these diseases to express themselves. However, this type of breeding can be partly remedied by mutation and natural selection provided the animal is allowed to reproduce without limit.

    This type of inbreeding really has nothing to do with the intent of the breeder. The features that kill the animal were hidden from the breeder because they were recessive. This type of inbreeding comes about if one tries to restrict the breeding to brother-sister-mother-father for a couple of generations. Hidden traits eventually kill the line. Whether the breeder tries to select for appearance or performance, the animal will get sick.

    Breeding for a specific feature can result in the feature being so exaggerated that it becomes a danger to the animal. This is especially dangerous when the animal is bred for appearance rather than performance. When an animal is bred to perform a certain action, the breeding will stop when the feature starts hurting the animals. When an animal is bred to appear a certain way, selection can continue even after the exaggerated feature starts killing the animal.

    Bull dogs are a good example. Originally, bull dogs were bred to fight bulls. The short muzzle and large head were useful in grabbing the bulls legs. Of course, bull dogs that had difficulty breathing were automatically eliminated. However, some people thought the short muzzle was so cute they wanted more. So some breeders bred bull dogs with a short muzzle that makes it hard to breath. Some breeds of bull dogs have to be born by Cesarian, because they have such large heads.

    Originally, grey hounds were bred to race other dogs. The result was a dog with a very narrow head. However, stupid grey hounds couldn't get to the finish line. So there was a limit on how narrow their heads could get. However, people started to breed greyhounds for a narrower head rather than how to race. The result is that some grey hounds are dumb as dirt.

    This type of inbreeding problem does not require brother-sister-mother-son mating. The problem was selecting for a feature with no feed back on health. Appearance does not always correspond to health. If one maximizes on appearance, one can have a very unhealthy line of animals.

    So both problems that you described occur. I don't know the relative importance of these inbreeding problems, but they are both dangers.
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