In humans, there are various cultural rules to avoid inbreeding (to the level of paternal cousins, nieces/nephews and uncles/aunts etc)
How do animals such as dogs avoid the problem of inbreeding? They do not have a record of their relatives and there seem to be many siblings in each batch for some animals. How does it work in the wild or among stray animals? Is their DNA somewhat resilient to these genetic disorders?
Likewise, how do birds handle this issue?
EDIT: I am not trying to breed animals, want to understand how it works in the uncontrolled wild when the young leave home early and are scattered.
The question is interesting. However, it will be impossible to answer accurately for all birds as the mechanisms actually used vary from species to species. So I will give you some information in the general sense.
Recurrent inbreeding reduces inbreeding depression
Inbreeding depression is caused by both
- Recessive deleterious alleles that are brought to homozygosity
- Some epistatic interaction
In any case, in a population where inbreeding is common, those recessive deleterious alleles and alleles involves in these deleterious epistatic combinations will be washed out (or at least brought to lower frequency) of the population via selection and the population will end up suffering less from inbreeding than a typical outbreeding population. In the extreme, a population of exclusively selfer individuals, such deleterious recessive alleles are brought to extremely low frequency within lineages.
How to avoid inbreeding?
Now, sure animals and plants typically don't have a big book that allow them to tell how related they are to another individual. However, there are other mechanisms of kin detection
For example, in plants self-incompatibility is thought to be relatively uncommon. There exist many mechanism, so I-ll just consider a simple example. Consider a self-incompatibility locus as a specific loci for which if the same allele is shared by both the pollen and the ovule, then no fertilization occurs. This prevents selfing and prevents mating with many of the closely related mechanisms.
Body odour and sexual attraction
Also, there are mechanism that can mediate sexual attraction toward individuals that differ. The classical example is Major histocompatibility complex (MHC) and sexual attraction (vertebrates), where individuals tend to be attracted to individuals that have a different MHC.
The term you are looking for is Kin Detection. which is the methods of recognizing related organisms, important both for avoiding inbreeding and aiding relatives.
There are several known mechanisms.
First they can avoid it the same way humans, they don't want to mate with anyone they were raised with. Humans don't need an understanding of genealogical to avoid mating with kin. Humans have an aversion to to romance with anyone they shared meals with frequently as a child. It is called the Westermarck effect or sometimes reverse imprinting and is part of humans in built kin detection system. It can work with many method just by building a brain that sees those who were around when you were a child as likely kin and thus unattractive to downright sexually repulsive. It is not perfect, it can be confused by adoption or separation, but works fairly well in the natural human setting. in effect their "record" is simply their memory.
Smell is another known method, in animals with better senses of smell than humans can detect certain factors that would indicate relatedness, like genetically controlled urinary proteins or simply smells of familiar and thus likely related individuals. This can work hand in hand with the Westermarck effect. There is even some very preliminary evidence humans may use this method to some extent.
Basic dispersal patterns can also do this by behaviorally programming one sex to travel far from where they are born and the other to not do this, it decreases the chance they will end up mating with a relative.
Now the formalized study of inbreeding avoidance is relatively new, mostly due to the technology making detecting kin for the scientists easier being new, so more and more research will almost certainly find other methods as well.
When Endangered Wildlife Gets Inbred
The endangered eastern lowland gorilla populations are now so small that the species is facing a new threat: loss of genetic diversity.
Gorillas can’t catch a break. Beset with habitat loss, poaching, political instability, and other threats, populations have plummeted. Now isolated in small populations, some eastern lowland gorillas are facing a new threat: loss of genetic diversity. As a population shrinks, the gene pool often shrinks as well. If the drop is severe enough, inbreeding may even threaten the survival of the species.
The decline in a population’s ability to survive through inbreeding is called inbreeding depression. But as discussed by biologists Philip Hedrick and Steven Kalinowski in Annual Reviews, inbreeding depression takes on different forms under different circumstances. Its impact on survival is not easily generalized. For a long-lived species such as gorillas, the overall impacts of inbreeding might take decades to manifest and are difficult to study.
Inbreeding is often studied in the lab using organisms like Drosophila (fruit flies), where a small population can be bred and examined over multiple generations. In such studies, as inbreeding increases, harmful mutations typically become more and more concentrated in the population through a process called unmasking, risking the population’s overall fitness. As a population becomes increasingly smaller and more inbred, harmful genetic conditions become more common.
Of course, genes do not operate in isolation. The interaction between genes and the environment is crucial. In some cases this might make inbreeding depression a moot point for endangered species, as external threats such as habitat loss may threaten extinction before inbreeding depression takes too much of a toll. Unfortunately, highly threatened species commonly live in stressful environments. In other words, their real world situation may be worse than models predict, and inbred populations face an even lower probability of survival than healthy populations.
Furthermore, a small population of a species in the wild is not the same as an artificially small population in a lab. A lab Drosophila population, for example, is a sample of all the vast genetic diversity of Drosophila available. For an actual small endangered population, overall genetic diversity is low and whatever genetic diversity happens to be present in the reduced population is all there is, a situation called a bottleneck. Sometimes that makes dangerous mutations common—and that can directly threaten extinction.
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Each gene has different variants, called alleles, that arise through mutation. One allele of a gene may confer a benefit, but a different allele of that same gene may cause harm. In a bottleneck, most of the various alleles, including the harmful ones, are uncommon. Sometimes a deadly allele is unmasked and manifests in an individual, killing that individual or preventing reproduction. Since the harmful allele is rare to begin with, that outcome removes those harmful alleles from the population. In such cases, inbreeding speeds up the loss of dangerous alleles, which may at least temporarily be beneficial. On the other hand, alleles that are harmful but not devastating are easily fixed in small populations, insidiously reducing fitness over time.
The good news is that sometimes inbreeding can be mitigated or even reversed by careful introduction of genes. This might mean reintroduction of captive-bred individuals, or selective transfer between isolated groups. Such actions themselves come with risks, but if inbreeding is dire enough, drastic action may be necessary.
Sporophytic Self-Incompatibility (SSI)
This form of self-incompatibility has been studied intensively in members of the mustard family (Brassica), including turnips, rape, cabbage, broccoli, and cauliflower.
- Rejection of self pollen is controlled by the diploid genotype of the sporophyte generation.
- The control lies in the "S-locus", which is actually a cluster of three tightly-linked loci:
- SLG (S-Locus Glycoprotein) which encodes part of a receptor present in the cell wall of the stigma
- SRK (S-Receptor Kinase), which encodes the other part of the receptor. Kinases attach phosphate groups to other proteins. SRK is transmembrane protein embedded in the plasma membrane of the stigma cell.
- SCR (S-locus Cysteine-Rich protein), which encodes a soluble ligand for the same receptor which is secreted by the pollen.
- Pollen will not germinate on the stigma (diploid) of a flower that contains either of the two alleles in the sporophyte parent that produced the pollen.
- This holds true even though each pollen grain being haploid contains only one of the alleles.
- In the example shown here, the S 2 pollen, which was produced by a S 1 S 2 parent, cannot germinate on an S 1 S 3 stigma.
- The S 1 S 2 pollen-producing sporophyte synthesizes both SCR 1 and SCR 2 for incorporation in (and later release from) both S 1 and S 2 pollen grains.
- If either SCR molecule can bind to either receptor on the pistil, the kinase triggers a series of events that lead to failure of the stigma to support germination of the pollen grain. Among these events is the ubiquination of proteins targeting them for destruction in proteasomes.
- If this path is not triggered (e.g., pollen from an S 1 S 2 parent on an S 3 S 4 stigma, the pollen germinates successfully.
You are correct there can be some very complex formulas for this. However, some of the basic questions depends on management. If they are willing/able to keep two separate breeding groups you can replace the bucks every 4 years without concern for inbreeding. If you want to get on a rotation to only need to replace one at a time you could replace the first at 2 years and each buck at 4 years in the herd after that. You would have some inbreeding but it would be a small level and should not cause any major issues.
If they run them in one breeding group or run both bucks with the does at all times then you need to shorten that to replacing every couple of years. Again, this can be done in a rotation but you would need to start sooner. With this system, you cannot be sure which buck breeds which females so you do not know the level of inbreeding in any individual. You can have sires breeding their daughters so you have to replace them more often.
I don’t know what the program has done other than what your question, so I have one caution to through out there. I have seen these programs fail in other places due to one issue. The animals need good nutrition to produce to the genetic potential. If you have not done so already, you may want to have some nutritional education with the group to make sure the animals are able to produce to their potential. Without proper nutrition and health care the animals will not last as long in the environment and they may not produce as much as expected. Just a caution, thought goats seem to do better in most of these areas than sheep or cattle.
Demerits of Inbreeding
The reasons why inbreeding is bad (disadvantages of inbreeding) are as follow:
- Adverse effect on the growth rate of animals: When inbreeding is continuously or intensely carried out, the growth rate and mature weight of the offspring (progeny) is negatively affected. That is, the growth rate and mature weight would moderately decrease.
- Adverse effect on reproductive performance: Another danger of continuous/intense inbreeding practice is that the reproductive performance or efficiency of the progeny will reduce. For example, puberty (testicular or ovarian development) may be delayed, gametogenesis (formation of gametes) may be reduced, and embryonic death rate may increase.
- Adverse effect on production: Economic traits in animals such as high litter number and size, high milk letdown or production, high carcass quality, high meat or egg production moderately decrease as you increase inbreeding.
- Adverse effect on animal’s vigor: Death/mortality rates tend to increase with continuous or intense inbreeding. Inbred (product of inbreeding) are also adversely affected by the environmental condition, and their resistance to diseases becomes reduced or weakened.
- Appearance of lethal or abnormalities: Inbreeding gives room for an often appearance of lethal traits or abnormalities such as cryptorchidism (absence of one or both testes firm the scrotum), parrot jaw etc.
Inbreeding is only advised if a livestock farmer:
- has deep knowledge about breeding
- wants to perform an experiment
- wants to preserve a pool of genes within a family line or breed
Knowing all these disadvantages of inbreeding, the best breeding system to practice is crossbreeding. The reasons why crossbreeding is recommended (advantages of crossbreeding) include:
- It is an effective way to introduce desirable characters that have not existed before into a breed. Also, it is used when a new breed is to be developed.
- Crossbred (product of crossbreeding) animals usually have and exhibit high vigor and rapid growth. They also perform better than their parents, such as produce more milk, eggs, wool, etc. than their parents or pedigree. In short, economic/productive traits significantly improve with crossbreeding.
Even though crossbreeding has its disadvantages which are majorly additional cost and a slight reduction in breeding merits of crossbred animals, its advantages outweigh its disadvantages.
So if you’re ready for business and you want to have quality and high performing animals on your farms, you must avoid mating animals of the same or related parents together. If possible, purchase your animals or starting stock from different sources. You must also keep breeding record of every animal on your farm.
In a situation where you are confused, or you need professional guidance, don’t hesitate to look for a professional or experienced animal breeder to put you through. The most important thing is to avoid inbreeding and always practice crossbreeding as recommended by breeding experts.
Please note that crossbreeding is not the only recommended breeding system, but it is the most common and most straightforward of all. There are other modern breeding systems but just stick to one recommended in this post.
How does a honeybee queen avoid inbreeding in her colony?
Recombination, or crossing-over, occurs when sperm and egg cells are formed and segments of each chromosome pair are interchanged. This process plays an crucial role in the maintenance of genetic variation. Matthew Webster and Andreas Wallberg at the Biomedical Centre, Uppsala University, have studied recombination in honeybees. The extreme recombination rates found in this species seem to be crucial for their survival.
Like other social insects, honeybees live in colonies consisting mainly of closely related members of the worker caste. High genetic diversity among the workers is important for the whole colony's survival. There are several theories as to why: for example, a genetically variable workforce may be best equipped to perform the diverse tasks required in the colony, and diverse colonies may also be less susceptible to disease. But how can the queen, the colony's only fertile female, prevent inbreeding and maintain genetic variation?
The queen bee solves the problem in two ways. One is through polyandry. She mates with a score of drones and uses their sperm to fertilize the eggs randomly so that workers often have different fathers. The second is through extremely high rates of recombination.
By sequencing the entire genome of 30 African honeybees, the research team has been able to study recombination at a level of detail not previously possible. The frequency of recombination in the honeybee is higher than measured in any other animal and is more than 20 x higher than in humans.
Recombination affects how efficiently natural selection can promote favorable genetic variants. In line with this, the researchers have found that genes involved in the new adaptations to the environment in honeybees also undergo more recombination. But recombination is not entirely risk free.
"Recombination is not only beneficial for bees. When parts of chromosomes broken and exchanged, errors can sometimes occur during their repair due to a process called "GC-biased gene conversion," says Matthew Webster.
This process leads to gradual fixation of mutations that may be harmful to the honeybee. Although a similar process occurs in humans, it is more than ten times stronger in honeybees. Over time, recombination is expected to lead to a deterioration of the gene pool, a process that seems to have accelerated in bees. The extreme recombination rates -- crucial for maintaining genetically diverse honeybee colonies -- come with a high price.
"There are no free lunches. Not even for a honeybee," says Matthew Webster.
Dominant and Recessive Genes
Ever wonder how some people get a particular eye color, even when their parents don&rsquot have that eye color? Or how some people don&rsquot inherit a particular disease, although their parent(s) have it? This is due to dominant and recessive genes.
Every person inherits one set of genes from each parent. Therefore, for a particular characteristic, every human has 2 genes. Now, both these genes could give us the same form of that trait or character, or they could give a different one. For example, a person could have both genes for a widow&rsquos peak hairline, or one gene for a widow&rsquos peak and the other gene for a straight hairline. In cases like this, one gene usually masks the other. This masking gene is a dominant gene, while the other is a recessive gene. This means that if both a dominant and recessive gene are present, then only the effect of the dominant gene will be visible. Therefore, for the effect of the recessive gene to be visible, both the genes must be recessive. Consider the following image. While &ldquoW&rdquo stands for a widow&rsquos peak hairline, &ldquow&rdquo stands for a straight hairline. As you can see, a straight hairline is a recessive trait.
Dominant and recessive genes.
Cross-Breed to Avoid Inbreeding
James Serpell is the Marie Moore professor of animal welfare at the School of Veterinary Medicine, University of Pennsylvania and the director of the Center for the Interaction of Animals and Society there.
Dog breeding and showing emerged as a middle-class hobby during the 19th century. The primary goal of these early hobbyists was to preserve and "improve" the distinguishing features of the various races or breeds of dogs that existed at the time. One way they achieved this was by developing written breed standards that defined the supposedly ideal characteristics of each breed.
There are two main problems with these breed standards. First, in order to produce dogs that met the standard, breeders employed breeding practices that inevitably resulted in inbreeding. Not only were the original gene pools of many breeds very small to begin with, but breeders have also accentuated the problem by selectively breeding from relatively small numbers of "champion sires" and/or by mating together closely related individuals.
Nowadays, many breeds are highly inbred and express an extraordinary variety of genetic defects as a consequence: defects ranging from anatomical problems, like hip dysplasia, that cause chronic suffering, to impaired immune function and loss of resistance to fatal diseases like cancer. The only sensible way out of this genetic dead-end is through selective out-crossing with dogs from other breeds, but this is considered anathema by most breeders since it would inevitably affect the genetic "purity" of their breeds.AP Photo/Ann Heisenfelt English bulldogs often have breathing problems.
The second problem is more subtle but equally harmful. Although the breed standards are carefully worded, they tend to be imprecise, and this allows a degree of ambiguity when it comes to interpretation.
Consider, for example, the written standard for the English bulldog’s face and muzzle: “the face, measured from the front of the cheekbone to the tip of the nose, should be extremely short, the muzzle being very short, broad, turned upward and very deep from the corner of the eye to the corner of the mouth.” As written, this description seems to require breeders to select for the shortest and most deformed face and muzzle possible, and for show judges to award their highest accolades to the dogs that best exemplify this trend. Is it any wonder then that bulldogs can no longer breathe properly?
This tendency for the primary distinguishing features of dog breeds to become more and more accentuated over time is extremely widespread, and in almost every case it has been detrimental to the health and welfare of the dogs.
When standards do more harm than good, they should either be revised or abandoned altogether. We owe it to the dogs.
How do animals avoid the problem of inbreeding? - Biology
During our programme on the 18th March 2017, Arnold Sciberras, founder of Maltese Land Races Initiatives, discussed with us the effects of inbreeding in animals and plants. Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically.
Mammals, most other animals, and higher plants as well, have evolved mechanisms to avoid inbreeding of any sort. Most pack animals (like lions, primates, and dogs), kick young males out of the pack so as to prevent them from mating with female relatives. Studies have found that animals living in complex social groups have no trouble recognizing their own kin’s calls, particularly the sounds of maternal relatives. Even goat mamas keep a long-term memory for their baby’s calls. Humans have very strong taboos against mating with relatives. Even fruit-flies apparently have a sensing mechanism to avoid too close of inbreeding, even in a closed population they maintain more genetic diversity than they ought to by random mating.
Inbreeding depression encompasses a wide variety of physical and health defects. Any given inbred animal generally has several, but not all, of these defects. These defects include:Elevated incidence of recessive genetic diseases
- Reduced fertility both in litter size and in sperm viability
- Increased congenital defects such as cryptorchidism, heart defects, cleft palates
- Fluctuating asymmetry (such as crooked faces, or uneven eye placement and size)
- Lower birth weight
- Higher neonatal mortality
- Slower growth rate
- Smaller adult size, and
- Loss of immune system function.
Yet Arnold explained that inbreeding is also used as a technique in selective breeding. In livestock breeding, breeders may use inbreeding when, for example, trying to establish a new and desirable trait in the stock, but will need to watch for undesirable characteristics in offspring, which can then be eliminated through further selective breeding or culling. Studies carried out by Arnold on lower Vertebrates and many invertebrate animals show that inbreeding amongst the latter in the most natural harsh conditions is beneficial in terms of species specialisation and speciation.
Arnold also explained the effects of inbreeding in plants, inbred lines for the creation of hybrid lines to make use of the effects of heterosis. Inbreeding in plants also occurs naturally in the form of self-pollination. Some, like sweet cherries, have even evolved elaborate biochemical mechanism to ensure that their flowers can not be fertilized by themselves or by very genetically similar individuals. For more info you can contact Arnold on his email address: [email protected]
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Connie - Well, Louise. That question all sounds a little Adam and Eve. And it's also something the naked scientists have been wondering. You see, we recently bought a desert island in the Pacific, and we want to avoid any sticky situations in the future. So, how many people do we need to start with to keep our island healthy? When I asked you on Facebook and Twitter, Glenn Fisher thought that only one was a safe bet, whilst Jay Michael Antovics II thought that it might depend on what definition we use. Maybe Professor Mike Weale, a statistical geneticist from King's College London can help us.
Mike - So, inbreeding means different things to different people. So, there no one single answer to this question. Everyone is related to their partner somehow, it's just a question of how far one needs to go back in time before a common ancestor is found.
Connie - Oh wow! So wait a minute! Does that mean I'm technically related to my boyfriend?
Mike - Technically, yes! I mean, to stop all relatedness between all mating partners, you would need, in fact, an infinite number of people.
Connie - Okay. I see. But our island isn't going to be infinitely big, and more importantly, I'm not sure I can stomach the idea of being related to my boyfriend. And that must also mean that absolutely everybody is inbred, which just doesn't feel quite right. Surely, there's another way?
Mike - Well. Yes. There is. To a population geneticist, the definition of inbreeding is simply a situation where mating partners are more closely related than what's expected by chance. So, using this definition all one needs to do to avoid inbreeding is to select mating partners purely by chance, as though you were in the lottery. And then, the population can be as small as you want. Well, you need to have at least two. But in a small population, even one that was enjoying some hedonistic version of the national lottery, mating partners will unavoidably tend to be more closely related to each other.
Connie - And I suppose that can't be good for the future?
Mike - Yep. In the short term, this increases the chances of people suffering from certain types of genetic diseases, diseases such as cystic fibrosis or Tay-Sachs disease, for example. This is because these diseases are caused by inheriting a bad genetic variant both from one's mother and from one's father. And the chances of them both having the same bad genetic variant are increased if they are closely related to each other.
Connie - Okay. So, where does that leave us then?
Mike - Ultimately, there's no magic population threshold that will make this problem go away. But a study in 2002 suggests that a population of 160 onboard a so called generation spaceship travelling to the stars should be able to keep itself genetically healthy. So, this would be a reasonable guideline for your desert island. In fact, real human populations on islands in the Pacific have survived population crashes down to as few as 20 people, but I wouldn't recommend this as a way to keep your desert island either healthy or happy.
Connie - Well. There we have it. It all depends on your definition. I think to be on the safe side, I'm going with at least a few hundred. Who wants to come?
Watch the video: Φιλοζωικό Σωματείο Κύμης - Αλιβερίου. Παγκόσμια Ημέρα Αδέσποτων Ζώων (January 2022).