Inbreeding depression confers reduced fitness among the offspring of genetic relatives. In spite of its prevalence, some researchers question whether inbreeding depression is important in wild populations, invoking two main arguments. Inbreeding depression is the reduced biological fitness in a given population as a result of inbreeding, or breeding of related individuals. Nov 06, 2018 other traits in which inbreeding depression has been documented for beef cattle include percentage weaned, birth weight, preweaning gain, weaning weight, postweaning gain, and final weight. Pdf the genetics of inbreeding depression researchgate. Where f x is the coefficient of inbreeding of individual x. Accumulation of deleterious mutations due to inbreeding in tiger population lauren begany c. The biological fitness is an organisms ability to survive and conserve its genetic material. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity. Jan 23, 2020 inbreeding occurs when two closely related organisms mate with each other and produce offspring. Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. Recent approaches into the genetic basis of inbreeding depression in plants. Inbreeding may or may not lead to inbreeding depression, which is a reduction in the fitness in the offspring produced by inbred matings.
The different sources of variation in inbreeding depression. Bottlenecks reduce genetic variation genetic drift northern elephant seals were reduced to 30 individuals in the 1800s. Inbreeding depression can reduce the performance of the progeny with consequences for populations and species persistence. Conversely, genetic load will be highest in species that have large population sizes and little inbreeding due to factors such as social organization which can subdivide. Although any of these genetic mechanisms could threaten population persistence, inbreeding poses the most immediate risk. We introduce an experimental design in which sires are mated to multiple dams, some of which are unrelated to the sire but others are genetically related owing. To understand the genetic basis of inbreeding depression and heterosis in rice, maineffect and epistatic qtl associated with inbreeding depression and heterosis for grain yield and biomass in five related rice mapping populations were investigated.
If we are to understand the evolution of inbreeding depression i. Accumulation of deleterious mutations due to inbreeding in. We define inbreeding depression for some sire i to be the expectation of the phenotypic difference between outbred progeny io and inbred progeny if, or in terms of genetic effects, 2 since we are interested in the variation in the differential effects of inbreeding across breeding individuals, we define the variation in inbreeding depression effects ide, i. The genetic interpretation of inbreeding depression and outbreeding depression. The genetic interpretation of inbreeding depression and. Inbreeding depression an overview sciencedirect topics. Inbreeding depression in plant breeding biotech articles. Little in 1909, with the subsequent creation of over inbred strains and stocks of mice festing, 1996. To gain insight into inbreeding depression in potato. Genetic decline and inbreeding depression in an extremely. Based on recent studies in many species, the authors argue that both. Rare alleles are likely to be lost during a bottleneck two important determinants of the severity of a bottleneck are the duration and population size ne nonrandom mating inbreeding.
Genetic interpretation of inbreeding and outbreeding 623 this paper is an attempt to put the con cepts of inbreeding depression, outbreeding enhancement, and outbreeding depression in a unifying framework and to provide a methodological basis for evaluating the ge. The house of habsburg may be the best example of the effects of inbreeding in humans. Fredrickson1, peter siminski2, melissa woolf 3 and philip w. Although inbreeding is a valuable breeding technique and one that can be combined with selection to improve response when h 2 is small or with crossbreeding to produce animals and plants that farmers grow for market, unplanned and uncontrolled inbreeding often leads to inbreeding depression. The two main negative consequences of inbreeding are an increased risk of undesirable genes and a reduction in genetic diversity. Inbreeding depression is important in the evolution of outcrossing mating systems and, because intercrossing inbred strains improves yield heterosis, which is important in crop breeding, the genetic basis of these effects has been debated since the early twentieth century. Pdf overdominant epistatic loci are the primary genetic.
Inbreeding depression as a measure of the cost of selffertilization slides 911. The genetic interpretation of inbreeding depression and outbreeding depression michael lynch department ofbiology, university oforegon, eugene, or 97403 usa abstract. Introduction about inbreeding depression, effect and degrees of inbreeding depression. Hedrick1, 1school of life sciences, arizona state university, tempe, az 852874501, usa 2the living desert, palm desert, ca 922606156, usa 3turner endangered species fund, ladder ranch, caballo, nm 87931, usa although inbreeding can reduce individual. Heterosis and inbreeding depression in f2 populations of.
Understanding inbreeding depression, purging, and genetic. Two identical alleles at the same locus can in some cases be the alternative with the highest fitness homozygote advantageunderdominance. Note that inbreeding will not make a difference for dominant traits because they need. Implications for protection and recovery of the genetic variation of extremely rare plants, such as o. The cause of this depression is the load of deleterious recessive alleles that are. A genetic interpretation of the variation in inbreeding. The genetic basis of inbreeding depression in potato. Overdominant epistatic loci are the primary genetic basis of. Lecture 27 effects of inbreeding mit opencourseware.
Loss of genetic diversity and inbreeding in new zealands. The widespread incorporation of genomic information in dairy cattle genetic evaluations allows for the opportunity to develop and implement methods to manage populations at the. Inbreeding is a fundamental genetic tool applied to the laboratory mouse and detailed information is available on the web table 3. Today we will examine how inbreeding between close relatives also known as consanguineous matings influences the appearance of autosomal recessive traits. Genetic drift impacting small populations and inbreeding. Genetic parameters, inbreeding depression and genetic trends were estimated for average daily gain between the ages of 510 weeks and thigh muscle volume measured in vivo with computerized tomography in a group of 22098 pannon terminal line rabbits born between 2006 and 2011 and reared in 3 396 litters. All inbreeding does not result in disaster when the use of inbreeding centers on genetically superior individuals. Understanding inbreeding depression, purging, and genetic rescue.
The genetic basis of reduced inbreeding depression in. It can be seen that the issues of heterosis and inbreeding depression have a common biological aspect. Inbreeding depression the reduced survival and fertility of offspring of related individuals occurs in wild animal and plant populations as well as in humans, indicating that genetic variation. Key terms biodiversity, inbreeding, heterozygosity, homozygous, inbreeding depression, deleterious, mutation, phenotype, genetic. The genetic basis of heterosis was studied through midparent, standard variety and better parent for 11 quantitative traits in 17 parental lines and their 10 selected hybrids in rice oryza sativa l. Bottlenecks reduce genetic variation genetic drift. Inbreeding reduces phenotypic performance inbreeding depression and the genetic variation due to mendelian sampling among progeny of a particular set of parents. As a clonally propagated crop, potato solanum tuberosum l.
In humans, its associated with consanguinity and incest, in which close relatives have sexual relationships and children. Jul 01, 2005 inbreeding depression is expected to play an important but complicated role in evolution. Hedrick1, 1school of life sciences, arizona state university, tempe, az 852874501, usa. Higher probability of inbreeding depression is expected when mating system shift from outcrossing or mixed mating to mainly selfing goodwillie et al. Inbreeding depression and outbreeding depression metapedia. The genetic basis of inbreeding depression and of the related phenomenon, heterosis, has been a puzzle for many decades. There are several genetic mechanisms which may cause outbreeding depression. Nov 11, 2011 a significant positive relationship between parental genetic dissimilarity and the number of surviving offspring was observed, which indicated that inbreeding depression might have purged more inbred offspring.
From the genealogists point of view the following are perhaps the two most interesting applications. This is the opposite of the effect which for other loci causes inbreeding depression. Inbreeding depression plays a significant role in crop breeding and in the evolution of outcrossing mating systems. The explanation of heterosis and inbreeding depression is the third case where the idea of ontogenes is used in order to resolve genetic problems. Inbreeding depression resulting from partially recessive deleterious alleles is thought to be the main genetic factor preventing selffertilizing mutants from spreading in outcrossing hermaphroditic populations. Recent approaches into the genetic basis of inbreeding. This pattern is the reverse of the magnitude of heritability for these classes of traits. The genetic basis of inbreeding depression genetics. Inbreeding is the process of mating genetically similar organisms. Inbreeding and inbreeding depression inbreeding is mating among relatives which increases homozygosity why is inbreeding a conservation concern. The genetic basis of reduced inbreeding depression in polyploids introduction inbreeding depression is the reduced fitness of inbred offspring relative to outbred offspring. Genetic rescue and inbreeding depression in mexican wolves.
Genetic parameters, inbreeding depression and genetic trends were estimated for average daily gain between the ages of 510 weeks and thigh muscle volume measured in vivo with computerized tomography in a group of 22098 pannon terminal line rabbits born. Breeding material used during the study of genetic potential, heterotic effects and inbreeding depression for yield related traits in 6. The hybrid breakdown part of inbreeding depression values of individual rils were negatively associated with the heterosis measurements of their bc or testcross hybrids, indicating the partial genetic overlap of genes causing hybrid breakdown and heterosis in rice. Recent estimates suggest that its impact on individual fitness is even greater than previously thought. Pdf inbreeding depression in the wild researchgate. Among 10 late onset conditions studied in a genetic isolate population, inbreeding was found to be a significant positive predictor for coronary heart disease, stroke, cancer, unibipolar depression, asthma, gout, and peptic ulcer, but not for type 2 diabetes. This phenomenon is well documented in all the major livestock species. Researchers take first look at the genetic dynamics of. Calculation and use of inbreeding coefficients for genetic. This result suggests that the genetic basis of inbreeding depression may differ among life stages. In brothersister mating or sib mating, the degree of inbreeding is high. Traditionally, pedigreebased relationship coefficients have been used to manage the inbreeding and degree of inbreeding depression that exists within a population. F is a very valuable parameter in both population and quantitative genetics. Inbreedingwith close relatives and outbreeding with members ofdistant populations can both result in deleterious shifts in the means offitnessrelatedcharacters, mostlikely for very.
Genetic basis of heterosis and inbreeding depression in. Researchers take first look at the genetic dynamics of inbreeding depression 12 march 2009 declines in reproductive success due to inbreeding are. Inbreeding depression has the greatest effect on reproductive traits, followed by growth traits, with little or no effect on carcass traits. The level of inbreeding depression has been suggested to determine a plants mating. The genetic basis of inbreeding depression in potato nature. Population biological fitness refers to an organisms ability to survive and perpetuate its genetic material.
Inbreeding violates modern social norms, but is fairly common in animals and plants. Measures of inbreeding inbreeding coeffi cients represent the homozygosity expected in an animals genome because of the relatedness of its parents. Genetic interpretation of inbreeding and outbreeding 623 this paper is an attempt to put the con cepts of inbreeding depression, outbreeding enhancement, and outbreeding depression in a unifying framework and to provide a methodological basis for evaluating the ge netic bases of these phenomena. Genetic basis of inbreeding depression in wiley online. The primary selfing rate of the tetraploid population was r 0. Deleterious mutations probably play a major role in causing inbreeding depression.
Epistasis, inbreeding depression and the evolution of self. Learn vocabulary, terms, and more with flashcards, games, and other study tools. Genetic parameters, genetic trends and inbreeding depression. Jan 14, 2019 inbreeding depression confers reduced fitness among the offspring of genetic relatives. Inbreeding and inbreeding depression 1 inbreeding and inbreeding depression 2 przewalskis horse 3 no transcript 4 ralls ballou 1983 5 back to inbreeding 6 chondrodystrophy in california condors q 0. To understand the genetic basis of inbreeding depression and heterosis in rice, maineffect and epistatic qtl associated with inbreeding depression and heterosis for grain yield and biomass in. Down, 17 july 1870 my dear lubbock, in england and many parts of europe the marriages of cousins are. The effects of a bottleneck on inbreeding depression and the. Abstract biodiversity in a species is the amount of genetic variability within the species. Inbreeding depression the reduced survival and fertility of offspring of related individuals occurs in wild animal and plant populations as well as in humans, indicating that genetic variation in fitness traits exists in natural populations.
The widespread incorporation of genomic information in dairy cattle genetic evaluations allows for the opportunity to develop and implement. Inbreeding depression ibd is the effect of inbreeding measured as the reduction in mean phenotypic performance with increasing levels of inbreeding within a population falconer and mackay, 1996. Inbreeding depression in fitness components or fitnessrelated traits is a focus in assessing these costs. The major hurdle that must be overcome in the development of new inbred strains from wild populations is inbreeding depression which occurs most strongly between the f 2 and f 8 generations second through eighth generation of sequential brothersister mating. Inbreeding depression is often the result of a population bottleneck. However, deleterious alleles may also generate an advantage to selfers in terms of more efficient purging, while the effects of epistasis among those alleles on inbreeding depression. Inbreeding depression in plants, caused by selfing or crossing among. Other research proves that inbreeding is the major cause of mutations in the tiger population and hopefully further research will be done on other possible mutations that could occur within the species. A significant positive relationship between parental genetic dissimilarity and the number of surviving offspring was observed, which indicated that inbreeding depression might have purged more inbred offspring. The importance of distinguishing between the two main genetic consequences of small population sizesloss of genetic diversity and inbreeding depression. Inbreeding depression, the reduction of fitness caused by inbreeding, is a nearly universal phenomenon that depends on past mutation, selection, and genetic drift. Genetic rescue and inbreeding depression in mexican wolves richard j. Published online20may2003 recent approaches into the genetic basis of inbreeding depression in plants david e.
The functional genomics of inbreeding depression oxford. Dudash2 1blandy experimental farm, university of virginia, 400 blandy farm lane, boyce, va 22620, usa. Inbreeding depression is expected to play an important but complicated role in evolution. When inbreeding depression is due to deleterious recessive alleles, the basic models predict that intermediate selfing rates are not evolutionarily stable and either. Genetic basis of heterosis and inbreeding depression in rice. Classical genetic studies and modern molecular evolutionary approaches now suggest that inbreeding depression and heterosis are. While linebreeding is less likely to cause problems in the first generation than does inbreeding, over time, linebreeding can reduce the genetic diversity of a population and cause problems related to a toosmall gene pool that may include an increased prevalence of genetic disorders and inbreeding depression. Inbreeding depression, purging and genetic rescue are recognized as elements to be considered in conservation programs, and genomic monitoring of. Genetic diversity refers to the total number of genetic characteristics in the genetic. Following the rediscovery of mendelian genetics, two main hypotheses were formulated to account for the existence of inbreeding depression and heterosis gain in fitness following outbreeding. Inbreeding is matting between individuals related by descent or ancestry. Ppt inbreeding and inbreeding depression powerpoint. Pdf despite its practical application in conservation biology and evolutionary theory, the cost of inbreeding in natural populations of plants and.
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