Low Inbreeding Coefficient Research Articles

Testing alternative captive breeding strategies with the subsequent release into the wild

We used the housefly (Musca domestica L.) as an experimental model to compare two strategies for the captive breeding of an endangered species: a strategy to minimize inbreeding and balance founder contributions (termed “MAI” for “maximum avoidance of inbreeding”) versus a scheme to select against less fit individuals (disregarding relatedness). By balancing the initial founder contributions, the MAI protocol was analogous to methods for minimizing kinship. In both breeding strategies, the population growth rate was limited to a maximum increase of 50% per generation. Five replicate populations, each starting with five male–female pairs, were subjected to five generations of captive breeding. Six generations of simulated “release into the wild” allowed ad lib breeding with less restrictive population growth potential, in either a benign or stressful environment (i.e., constant or variable temperature). Population size, fecundity, and fertility were assayed throughout the experiment, with juvenile-to-adult survival assayed in the second phase of the project. Allozyme assays determined the resultant inbreeding coefficients from the captive breeding schemes. The MAI breeding scheme resulted in significantly lower inbreeding coefficients and higher fitness, with qualitatively reduced extinction potential, most notable in the stressful environment. Spontaneous fitness rebounds suggested that the MAI strategy facilitated some form of purging of inbreeding depression effects. Importantly, the advantages of the MAI strategy were difficult to detect during the captive breeding phase, suggesting that the long-term advantages of the MAI approach could be underestimated in actual breeding programs. We concur with the common recommendation of maximum avoidance of inbreeding at least for systems with low reproductive potential. Zoo Biol 0:1–18, 2005. © 2005 Wiley-Liss, Inc.

Breeding value evaluation in Polish fur animals: Statistical description of fur coat and reproduction traits - relationship and inbreeding

Three data sets were available: records on conformation and coat traits for the arctic fox from one farm (5 540 observations, collected between 1983 and 1997), and the same traits for the silver fox from three farms (8 199 observations, collected between 1984 and 1999). The third set comprised 5 829 observations on reproductive performance of the arctic fox from one farm, collected between 1984 and 1999. The GLM procedure was used to test the significance of fixed effects on the analysed reproduction traits as well as differences between groups. Phenotypic trends as well as relationship and inbreeding across the studied years were computed. Most of the phenotypic trends were positive. Low relationship and inbreeding coefficients in the arctic and silver fox populations under study were estimated. The average relationship coefficients for the silver and arctic fox populations were 0.015 and 0.010, respectively, whereas the average inbreeding coefficients for the same species were 0.0039 and 0.0016, respectively. No inbreeding was found in the arctic fox breeding females.  

Family-level covariation between parasite resistance and mating system in a hermaphroditic freshwater snail.

Genetic compatibility, nonspecific defenses, and environmental effects determine parasite resistance. Host mating system (selfing vs. outcrossing) should be important for parasite resistance because it determines the segregation of alleles at the resistance loci and because inbreeding depression may hamper immune defenses. Individuals of a mixed mating hermaphroditic freshwater snail, Lymnaea ovata, are commonly infected by a digenetic trematode parasite, Echinoparyphium recurvatum. We examined covariation between quantitative resistance to novel parasites and mating system by exposing snail families from four populations that differed by their inbreeding coefficients. We found that resistance was unrelated to inbreeding coefficient of the population, suggesting that the more inbred populations did not carry higher susceptibility load than the less inbred populations. Most of the variation in resistance was expressed among the families within the populations. In the population with the lowest inbreeding coefficient, resistance increased with outcrossing rate of the family, as predicted if selfing had led to inbreeding depression. In the other three populations with higher inbreeding coefficients, resistance was unrelated to outcrossing rate. The results suggest that in populations with higher inbreeding some of the genetic load has been purged, uncoupling the predicted relationship between outcrossing rate and resistance. Snail families also displayed crossing reaction norms for resistance when tested in two environments that presented low and high immune challenge, suggesting that genotype-by-environment interactions are important for parasite resistance.

Relationships between Distribution of Number of Transferable Embryos and Inbreeding Coefficient in a MOET Dairy Cattle Population

Genetic gains and inbreeding coefficients in a Holstein MOET breeding population were predicted under different conditions relating to the distribution of the number of transferable embryos collected per flush using MonteCarlo simulation. The numbers of transferable embryos collected per flush were determined using five distributions (distributions 1, 3, 5, 7 and 9) with different aspects and similar means. Distributions 1, 3, 5, 7 and 9 were assumed to have gamma distribution's parameters (a and β) of (1 and 4.4), (3 and 1.47), (5 and 0.88), (7 and 0.63) and (9 and 0.49), respectively. Inbreeding rates were statistically significantly different among distributions but genetic gains were not. Relationships between inbreeding rates and variances of family size could be were clearly distinguished. The highest inbreeding coefficients were predicted in distribution 1 with the largest variance of family size, while distributions 5, 7 and 9 with smaller variance of family size had lower inbreeding coefficients.

Mental retardation in Norway: prevalence and sub-classification in a cohort of 30037 children born between 1980 and 1985.

We wanted to determine the prevalence and subcategories of mental retardation (MR) defined as IQ < or = 70 in Akershus county, which rated by average yearly income, had the second highest socioeconomic status (SES) in Norway. The study population consisted of 30 037 children born between 1980 and 1985. Cases were ascertained from multiple sources and psychometrically assessed, predominantly with the Wechsler tests, which were standardized in Norway in 1978. The cases were divided into four groups: profound (IQ < 20), severe (IQ 20-34), moderate (IQ 35-49), and mild (IQ 50-70) MR, according to the Diagnostic and Statistical Manual of Mental Disorders, 4th edition (DSM-IV). The median age was 10.8 y. The frequency and degree of parental consanguinity were registered, and the average inbreeding coefficient was calculated. Altogether, 185 had IQ < or = 70, giving a prevalence of MR of 6.2/1000. Prevalences for profound, severe, moderate, and mild MR were 0.8, 0.4, 1.5 and 3.5/1000, respectively. In two, possibly three, cases the parents were second cousins, giving an average inbreeding coefficient of 20-30 x 10(-5). The low prevalence of MR, particularly mild MR, could partly be explained by high SES, old standardization of IQ-test, and low inbreeding coefficient. The proportion of profound MR was considerably higher than estimated by DSM-IV.

Effect of Excluding Sib Matings on Inbreeding Coefficient and Effective Size of Finite Diploid Populations

The effects of excluding full-sib matings, half-sib matings, or both under random selection or equal family size selection on the inbreeding coefficient and effective size in finite populations with unequal sex ratio have been studied. Recurrent equations for the inbreeding coefficient and approximate formulas for effective size are derived for different breeding systems. It is shown that avoidance of sib matings results in lower inbreeding coefficients in any generations under random selection. Under equal family size selection, however, excluding sib matings gives rise to lower inbreeding coefficients only in the first few generations and will eventually result in a higher inbreeding in later generations compared with random mating. Exclusion of sib matings increases effective size under random selection while it decreases effective size under equal family size selection. The relative effectiveness on effective size of different sib mating avoidance depends only on sex ratio of the population. The importance of full-sib mating decreases and that of half-sib mating increases with the increment of the value of sex ratio (r). When r = 3, full-sib mating has the same effect on effective size as half-sib mating.

The Genetic Composition and Tetrasomic Inbreeding Coefficients of Highbush Blueberry Cultivars

Inbreeding coefficients were calculated for highbush blueberry (Vaccinium corymbosum L.) cultivars based on a tetrasomic inheritance model. This model yielded lower inbreeding coefficients than previous calculations based on a disomic tetraploid inheritance model. Recent trends in breeding have resulted in significant use of V. darrowi Camp as a source of low-chilling germplasm for use in the southern United States. There is also a trend toward increased inbreeding in several crosses from which recently released cultivars have been derived. Increased inbreeding coefficients do not represent a detrimental situation in blueberry per se.

Models for the evolution of selfing under alternative modes of inheritance

In an approach that explicitly incorporates genetic changes over consecutive generations of self-fertilization, we contrast the effect of different modes of inheritance for selfing rate upon the evolutionary equilibrium selfing rate. A monotonic decline of fitness with consecutive generations of selfing was assumed. We found the range of conditions permitting evolutionarily stable mixed-mating systems to increase with the number of genes controlling the selfing rate. When the mating system is controlled by a single locus with alternative alleles for complete selfing or outcrossing, alleles for selfing concentrate in inbred individuals and are exposed to stronger selection than the average inbreeding depression. By contrast, when alleles of small effect control the selfing rate, selfing rates do not vary as much between inbred vs. outcrossed individuals; this results in the broader stability of mixed mating. We also find that, provided selfing is not caused by recessive alleles, low levels of outcrossing can be maintained when the average relative fitness of selfed progeny is above 0.5. This is postulated to be due to a long-term advantage for occasional outcrossing in terms of the restoration of low inbreeding coefficients. The assumption of a mono-tonic decline in fitness with consecutive generations of selfing is also discussed.

Genetic Diversity of Red Raspberry Varieties throughout the-World

Pedigrees of 137 red raspberry (Rubus idaeus L.) varieties released throughout the world since 1960 were used to calculate: 1) the genetic contribution of founding clones to these varieties; 2) genetic relatedness among them; and 3) their inbreeding coefficients. Fifty founding clones contributed to the pedigrees of these varieties with a mean genetic contribution ranging from &lt;0.1% to 21%. Varieties were clustered according to the genetic contribution into groups strongly related to geographical origin. Varieties developed in the former USSR and derived from `Novost Kuzmina' formed a distinct cluster. The remaining varieties were clustered in groups based mainly on whether they were of North American or European origin. Varieties were clustered also on the basis of Wright's coefficient of relationship-a measure of genetic relatedness. Cluster groups were related to their geographical origin and the varieties within the groups could be traced to similar intermediate parents. Inbreeding coefficients ranged from 0.0 to 0.625 and were related, in part, to the numbers of generations of controlled hybridization from common ancestors. The British group, with the largest number of generations of breeding, had a low mean inbreeding coefficient, indicating that inbreeding can be minimized with attention to the mating system. Strategies are suggested for maintaining and increasing the genetic diversity in the world's red raspberry breeding populations.

Accounting for Inbreeding and Crossbreeding in Genetic Evaluation of Large Populations

Inbreeding coefficients for 9.3million registered Holsteins were computed by constructing a small relationship matrix for each animal and its ancestors instead of one large matrix for the whole population. Recent cows averaged 2.0% inbreeding if each pedigree path was extended to the most recent ancestor born before 1960. Inbreeding was underestimated because some pedigrees included unknown ancestors more recent than the defined base year. Alternative estimates of inbreeding can be derived by assigning mean relationship and inbreeding of known ancestors to unknown ancestors of the same period. Animals of different breeds are less related than animals of the same breed. Relationships and inbreeding within and across populations can be measured back to the common base population from which the breeds arose by treating earliest known ancestors within each breed as related and inbred. Increased heterozygosity and heterosis of crossbred animals are then predicted from their lower inbreeding coefficients. Relationship matrices that include related and inbred unknown-parent groups treated as random or fixed effects can be constructed and inverted quickly.

Comparative analysis of mating systems and marriage distance patterns in five tribal groups of Andhra Pradesh, India.

Abstract Various studies on marriage patterns in India have indicated that the incidence of consanguineous marriages varies according to linguistic groups. This study was carried out in an area of culture contact of several different linguistic groups. A study of five endogamous tribal groups showed that the degree of consanguinity and type of consanguineous marriages were closely related to the linguistic area to which each population belonged. The Raj Gonds, Kolams, and Pradhans had a high inbreeding coefficient similar to that of rural populations of Andhra Pradesh; the Andhs showed a lower coefficient similar to that of Maharashtra, their area of origin; and the Mathuras, a nomadic North Indian group, showed a very low inbreeding coefficient, which is characteristic of North India.

Estrus in range lambs and its relationship to life-time reproductive performance.

The occurrence of estrus in lambs the first winter as related to subsequent lamb production was studied in 2,364 Rambouillet, 1,956 Targhee and 1,350 Columbia ewes. These ewes made one to five lambing records. Twelve percent of the lambs exhibited heat their first winter. The differences among years within breeds were highly significant for each breed. However, the years having a high or low incidence of estrus do not correspond for the three breeds indicating a year-breed interaction. About 60% had one heat period, 25% two heat periods and only 2% had as many as five heat periods. The lambs which came into heat had lower inbreeding coefficients, less face covering, better condition scores, heavier weaning weights, were slightly older and had heavier yearling fall bodyweights than lambs that did not come into heat. The cumulative lamb production was without exception greater for ewes which showed estrus as lambs than for those which did not. The effect was greatest in the Rambouillet breed, being significant for all cumulative lamb production traits but one. Targhee ewes showed an important and significant positive association of estrus and production for the first 3 yr. of production but little association thereafter. The Columbias showed an apparent effect in favor of ewes showing estrus as lambs. However, this was significant only for the lifetime kilograms of lamb weaned per ewe for ewes completing five production records. Rambouillet, Targhee and Columbia ewes showing estrus as lambs accumulated an average of 20.4, 10.9 and 19.1 kg. of lamb more per ewe, respectively, over five production years than those which did not come into heat. There was no significant association of early estrus and lifetime wool production, although in two of the three breeds lifetime grease fleece weights were slightly lower for the groups showing estrus their first winter.