Mean Kinship Research Articles

The impact of assumptions about founder relationships on the effectiveness of captive breeding strategies

Many breeding programs managed by zoos and aquariums employ strategies that minimize mean kinship as a way of retaining genetic diversity (MK strategies). MK strategies depend on accurate and complete pedigrees, but population founders are generally assumed to be unrelated and not inbred. This assumption was historically necessitated by the unavailability of data on founder relationships, but with DNA techniques it is sometimes now possible to estimate those relationships. We used computer simulations to investigate the impact of founder assumptions on the effectiveness of MK strategies. Individuals with known pedigrees were managed in groups of 10, 30, and 100 founders at two different rates of reproduction and two different degrees of founder relationship. The impact of assuming founders were unrelated was quantified by calculating the differences in gene diversity and inbreeding that were observed between simulations that used known relationships and simulations that assumed founders were unrelated. Results indicated that utilizing known relationships retained 0–2% more gene diversity over ten generations than assuming founders were unrelated, with specific results dependent on the conditions of a given scenario. Similar results were observed for inbreeding, with long-term levels of inbreeding being 0–2% lower when relationships were known. There were higher benefits to knowing founder relationships as reproductive rate increased, as well as when full-siblings were included in small groups of founders. Overall, however, long-term benefits gained from knowing founder relationships were generally small. Therefore, MK strategies probably often produce near optimal results when standard founder assumptions are made.

Relationship between genealogical and microsatellite information characterizing losses of genetic variability: Empirical evidence from the rare Xalda sheep breed

Preservation of rare genetic stocks requires continual monitoring of populations to avoid losses of genetic variability. Genetic variability can be described using genealogical and molecular parameters characterizing variation in allelic frequencies over time and providing interesting information on differentiation that occurred after the foundation of a conservation program. Here we analyze the pedigree of the rare Xalda sheep breed (1851 individuals) and the polymorphism of 14 microsatellites in 239 Xalda individuals. Individuals were assigned to a base population (BP) or 4 different cohorts (from C1 to C4) according to their pedigree information. Genetic parameters were computed at a genealogical and molecular level, namely inbreeding ( F), observed ( H o) and expected ( H e) heterozygosity, individual coancestry coefficients ( f and f m), average relatedness (AR), mean molecular kinship (Mk), average number of allele per locus ( A), effective number of ancestors ( f a ), effective population size ( N e and N e(m)) and founder genome equivalents ( N g and N g(m)). In general, the computed parameters increased with pedigree depth from BP to C4, especially for the genealogical information and molecular coancestry-based parameters ( f m, Mk and N g(m)). However, H o and H e showed the highest values for C1 and the molecular heterozygote deficiency within population ( F IS(m)) showed the lowest value for C1, thus indicating that loss of genetic variability occurs very soon after the implementation of conservation strategies. Although no genealogical or molecular parameters are sufficient by themselves for monitoring populations at the beginning of a conservation program, our data suggests that coancestry-based parameters may be better criteria than those of inbreeding or homozygosity because of the rapid and strong correlation established between f and f (m). However, the obtaining of molecular information in well-established conservation programs could not be justified, at least in economic terms.

A common genetic background for inflammatory bowel disease and ankylosing spondylitis: A genealogic study in Iceland

Patients with ankylosing spondylitis (AS) and approximately 50% of their first-degree relatives may have a genetic abnormality that results in subclinical intestinal inflammation. This study was undertaken to examine the familial occurrence and cosegregation of AS and inflammatory bowel disease (IBD) in order to determine whether there is a shared genetic risk factor in families. The Icelandic genealogy database and population-wide data on all living Icelanders diagnosed as having AS (n = 205) and/or IBD (n = 1,352) were used to estimate the risk ratios of AS for relatives of patients with AS, the risk ratios of IBD for relatives of patients with IBD, and the cross-risk ratios of AS for relatives of patients with IBD or of IBD for relatives of patients with AS. The mean kinship coefficients for each disease were calculated. The control population for disease risk calculations comprised 10,000-100,000 sets of matched Icelandic subjects. First-, second-, and third-degree relatives of patients with AS had risk ratios of 94, 25, and 3.5, respectively, indicating an increased risk of developing AS (each P < 0.0005), while first-, second-, and third-degree relatives of patients with IBD had risk ratios for IBD of 4.4, 2.2, and 1.4, respectively (each P < 0.0001). The cross-risk ratios of IBD were 3.0 and 2.1 in first- and second-degree relatives of patients with AS, respectively, and were the same for AS in first- and second-degree relatives of patients with IBD. With the exception of Crohn's disease, the risk of having AS, ulcerative colitis, or IBD in spouses of patients with these diseases did not differ significantly from that in controls. Calculation of the kinship coefficients confirmed these patterns of familial risk. Patients with AS or IBD in Iceland are significantly more related to each other than are randomly sampled control subjects, in terms of an increased risk of either or both conditions developing in third-degree relatives. These findings suggest that one or more undiscovered genetic variants may underlie the risk of both diseases.

Captive breeding and the reintroduction of Mexican and red wolves

Mexican and red wolves were both faced with extinction in the wild until captive populations were established more than two decades ago. These captive populations have been successfully managed genetically to minimize mean kinship and retain genetic variation. Descendants of these animals were subsequently used to start reintroduced populations, which now number about 40-50 Mexican wolves in Arizona and New Mexico and about 100 red wolves in North Carolina. The original captive Mexican wolf population was descended from three founders. Merging this lineage with two other captive lineages, each with two founders, has been successfully carried out in the captive population and is in progress in the reintroduced population. This effort has resulted in increased fitness of cross-lineage wolves, or genetic rescue, in both the captive and reintroduced populations. A number of coyote-red wolf hybrid litters were observed in the late 1990s in the reintroduced red wolf population. Intensive identification and management efforts appear to have resulted in the elimination of this threat. However, population reintroductions of both Mexican and red wolves appear to have reached numbers well below the generally recommended number for recovery and there is no current effort to re-establish other populations.

Spatial demographic and genetic consequences of harvesting within populations of the terrestrial orchid Cymbidium goeringii

Populations of many orchids, especially terrestrial species, have been rapidly decreasing due to mass collection by plant sellers and enthusiasts. Given the presumably negative demographic and genetic consequences, such anthropogenic activity should be taken into consideration for predicting ecological and evolutionary dynamics and for planning conservation strategies. To determine how recent human disturbance alters spatial demographic and population genetic processes, populations of the terrestrial orchid Cymbidium goeringii located in South Korea were examined to quantify the spatial distributions of individuals and genotypes with respect to three levels of disturbance: “disturbed” (four populations), “putatively disturbed” (two), and “undisturbed” (two). Undisturbed and putatively disturbed populations were found to possess significantly positive spatial clustering of individuals over a range of spatial scales. In contrast, disturbed populations exhibited little or no spatial aggregation, consistent with the selective removal of plants by collectors from higher density areas within these populations. Although overall genetic differentiation among populations was moderate and significant ( F ST = 0.082), levels of genetic diversity within populations were similar despite the different disturbance histories (mean H e = 0.257–0.324). Spatial genetic autocorrelation analyses revealed that the undisturbed populations exhibited significant declines in kinship ( F ij ) with distance, that mean kinship at interplant distances of ⩽4–6 m was significantly greater than zero and between plants ⩽0.5 m apart was in the range expected for first cousins to half-sibs. In contrast, only one putatively disturbed and one disturbed population exhibited significant declines in kinship with distance. These differences between disturbed versus putatively disturbed and undisturbed populations in the spatial distribution of individuals and genetic variation likely reflect the consequences of mass collections. Since these differences (and reduced population density) have important implications for future ecological and evolutionary trajectories, conservation managers of endangered terrestrial orchids may want to analyze the spatial distribution of individuals and their genotypes to infer whether a population with few individuals represents a natural state or the likely outcome of mass collection.

Genetic diversity loss due to selection for scrapie resistance in the rare Spanish Xalda sheep breed

The effect of selection for scrapie resistance on genetic variability in the rare Xalda sheep breed was studied. Pedigree information comprised 1851 animals (1444 alive) at the moment of sampling. A total of 304 reproductive (or selected for reproduction) Xalda individuals were sampled and genotyped for 14 microsatellites. Genetic variability was assessed using: gene diversity (1 − average kinship, GD), mean average relatedness (AR) and self-coancestry ( c i ) at the genealogical level; and expected heterozygosity ( H e), molecular mean kinship (Mk), molecular self-coancestry ( s i ) and rarefacted average number of alleles per locus ( A) at the molecular level. Two breeding strategies were evaluated: a) use of only young rams with genotype ARR/ARR and young ewes with low to moderate risk (risk groups R1 to R3); b) breeding without selection for PrP genotypes. The major cause of losses of genetic variability in the Xalda breed is the drift that occurs when a new group of reproductive individuals is selected. The loss of genetic variability is small in females compared to the males, where it is considerable. However, losses at the molecular level for young females with respect to adult females were above 5%. Young male individuals also retained most of the genetic variability assessed in adult rams. Selection against susceptibility to scrapie produced additional losses of more than 2% for H e and A when rYF individuals are considered. As regards males, the situation becomes critical because of the scant number of available ARR/ARR young rams. The consequences for the management of the Xalda breed are discussed.

Haplotype kinship for three populations of the Goettingen minipig

To overcome limitations of diversity measures applied to livestock breeds marker based estimations of kinship within and between populations were proposed. This concept was extended from the single locus consideration to chromosomal segments of a given length in Morgan. Algorithms for the derivation of haplotype kinship were suggested and the behaviour of marker based haplotype kinship was investigated theoretically. In the present study the results of the first practical application of this concept are presented. Full sib pairs of three sub-populations of the Goettingen minipig were genotyped for six chromosome segments. After haplotype reconstruction the haplotypes were compared and mean haplotype kinships were estimated within and between populations. Based on haplotype kinships a distance measure is proposed which is approximatively linear with the number of generations since fission. The haplotype kinship distances, the respective standard errors and the pedigree-based expected values are presented and are shown to reflect the true population history better than distances based on single-locus kinships. However the marker estimated haplotype kinship reveals variable among segments. This leads to high standard errors of the respective distances. Possible reasons for this phenomenon are discussed and a pedigree-based approach to correct for identical haplotypes which are not identical by descent is proposed.

Haplotype kinship for three populations of the Goettingen minipig

To overcome limitations of diversity measures applied to livestock breeds marker based estimations of kinship within and between populations were proposed. This concept was extended from the single locus consideration to chromosomal segments of a given length in Morgan. Algorithms for the derivation of haplotype kinship were suggested and the behaviour of marker based haplotype kinship was investigated theoretically. In the present study the results of the first practical application of this concept are presented. Full sib pairs of three sub-populations of the Goettingen minipig were genotyped for six chromosome segments. After haplotype reconstruction the haplotypes were compared and mean haplotype kinships were estimated within and between populations. Based on haplotype kinships a distance measure is proposed which is approximatively linear with the number of generations since fission. The haplotype kinship distances, the respective standard errors and the pedigree-based expected values are presented and are shown to reflect the true population history better than distances based on single-locus kinships. However the marker estimated haplotype kinship reveals variable among segments. This leads to high standard errors of the respective distances. Possible reasons for this phenomenon are discussed and a pedigree-based approach to correct for identical haplotypes which are not identical by descent is proposed.

Phenotypic Subtypes in Attention Deficit Hyperactivity Disorder in an Isolated Population

We address the use of two informants in genetic studies and whether familial aggregation is similar for the three phenotypic subtypes of ADHD. Lifetime ADHD was diagnosed in a Dutch isolated population using parents and teachers as informants, creating two subgroups (one or two informants), then further divided into three phenotypic categories (inattentive, hyperactive/impulsive, combined). Genealogy was collected for all patients. Mean kinship coefficients for the subgroups were calculated. Fifteen of 26 children were linked to a common ancestor within 10 generations. The mean kinship coefficient of patients confirmed by two informants was significantly higher than in patients only scored positive by one informant (p = 0.03). All patients of the inattentive subtype were connected to a common ancestor, which was significantly higher (p = 0.03) than expected. Eighty-one percent of these patients derive of consanguineous marriages, also higher than expected. This means that recessive mutations may be involved in the inattentive subtype. These patients were more closely related than those with the other phenotypes (p<0.01). Our data suggests that using two informants in diagnosing ADHD helps identify a phenotype with a strong genetic component. The inattentive phenotype showed strong familial clustering and evidence of a recessive origin.

Pedigree analysis of Polish Arabian horses based on founder contributions

The genetic structure of Polish Arabian horses over 50 years of breeding was studied based on founder contribution analysis. Data from 1032 brood mares and 154 sires in national studs, between 1948 and 1997, were analysed. Postwar Arabs are descended from 213 founders. During 50 years of breeding, there were increases in both the average number of founders in one pedigree (from 67.19 to 158.87) and in the proportion of the founders appearing in every pedigree (from 0% to 38.4%). The increase in mean kinship and inbreeding coefficient were also found. These results may be recognised as evidence of a reduction in genetic diversity of Polish Arabian horses.

A genetic contribution to inflammatory bowel disease in Iceland: A genealogic approach

Both genetic and environmental factors play a role in the development of Crohn's disease (CD) and ulcerative colitis (UC), collectively known as inflammatory bowel disease (IBD). The aim of this study was to estimate the genetic component in IBD in Iceland. A population-based sample, representing everyone diagnosed with IBD in Iceland from 1950 to 1996, was studied using a computerized population-wide genealogic database. The relationships among the patients were analyzed by calculating the kinship coefficient and the relative risk. The kinship coefficients for the patients were significantly greater than the mean kinship coefficient for the controls ( P < 10 -6 ). The risk ratio for siblings of IBD, UC, and CD patients was 5.0 ( P < 0.001), 5.9 ( P < 0.001), and 4.1 ( P = 0.033), respectively. The cross-risk ratio for siblings of UC patients developing CD (or vice versa) was 2.6 ( P = 0.015). The results indicate that the IBD patients are more closely related than the controls, which strongly supports the involvement of a genetic component in the development of IBD in Icelandic patients. We find that the increase in risk for relatives of UC probands to develop UC, or relatives of CD probands to develop CD, is greater than the increase in risk for relatives of UC probands to develop CD, or relatives of CD probands to develop UC.

GENETIC STATUS AND MANAGEMENT OF CALIFORNIA CONDORS

The last wild California Condor (Gymnogyps californianus) was brought into captivity in 1987. Captive breeding was successful and reintroduction efforts began in 1992. The current population is descended from 14 individuals belonging to three genetic “clans.” This population bottleneck led to the loss of genetic variation and changes in allele frequencies, including a probable increase in the frequency of the putative allele for chondrodystrophy, a lethal form of dwarfism. We use studbook data to analyze the current genetic and demographic status of the population and explain how it is managed to meet specific goals. In August 2002 the population consisted of 206 individuals distributed among three captive-breeding facilities and three reintroduction sites. The population is managed to preserve genetic diversity using the concept of mean kinship. Growth of the total population has been between 10% and 15% per year since 1987, but the growth of the captive population has been only about 5% per year since 1992 due to the removal of chicks for reintroduction. Assuming that founding birds within clans were half-siblings, the birds used to found the captive population theoretically contained 92% of the heterozygosity present in the hypothetical wild base population. About 99.5% of this heterozygosity has been retained in the current population. Alleles from most founders are well represented across captive- breeding facilities and reintroduction sites. The genetic status of this population compares favorably with other species that have been rescued from extinction by captive breeding. Situación Genética y Manejo de Gymnogyps californianus Resumen. El último cóndor californiano (Gymnogyps californianus) silvestre fue puesto en cautiverio en 1987. La reproducción en cautiverio fue exitosa y las reintroducciones comenzaron en 1992. La población actual desciende de 14 individuos pertenecientes a tres “clanes” genéticos. Este cuello de botella poblacional dió lugar a la pérdida de variabilidad genética y a cambios en la frecuencia de alelos, incluyendo un probable incremento en la frecuencia del alelo para condrodistrofia, una forma letal de enanismo. En este estudio, utilizamos datos del libro genealógico para analizar la situación genética y demográfica actual de la población y para explicar cómo se está manejando la población para cumplir con metas específicas. En agosto del 2002 la población consistía de 206 individuos distribuidos en tres instalaciones de reproducción en cautiverio y tres sitios de reintroducción. La población fue manejada con el propósito de conservar la diversidad genética usando el concepto de parentesco medio. El crecimiento de la población ha sido de entre 10% y 15% por año desde 1987, pero el crecimiento de la población en cautiverio ha sido únicamente de aproximadamente un 5% por año desde 1992 debido a la remoción de los pollos para su reintroducción. Suponiendo que los cóndores fundadores dentro de cada clan eran medio- hermanos, las aves que fueron utilizadas para fundar la población en cautiverio teóricamente contienen un 92% de la heterocigosidad presente en la población silvestre base hipotética. Cerca de un 99.5% de esta heterocigosidad ha sido retenida en la población actual. Alelos de la mayoría de los fundadores están bien representados en las diversas instalaciones de reproducción en cautiverio y sitios de reintroducción. La situación de esta población parece ser mejor que la de otras especies silvestres que han sido rescatadas por medio de la reproducción en cautiverio.

Assessing the�contribution of�breeds to�genetic diversity in�conservation schemes

The quantitative assessment of genetic diversity within and between populations is important for decision making in genetic conservation plans. In this paper we define the genetic diversity of a set of populations, S, as the maximum genetic variance that can be obtained in a random mating population that is bred from the set of populations S. First we calculated the relative contribution of populations to a core set of populations in which the overlap of genetic diversity was minimised. This implies that the mean kinship in the core set should be minimal. The above definition of diversity differs from Weitzman diversity in that it attempts to conserve the founder population (and thus minimises the loss of alleles), whereas Weitzman diversity favours the conservation of many inbred lines. The former is preferred in species where inbred lines suffer from inbreeding depression. The application of the method is illustrated by an example involving 45 Dutch poultry breeds. The calculations used were easy to implement and not computer intensive. The method gave a ranking of breeds according to their contributions to genetic diversity. Losses in genetic diversity ranged from 2.1% to 4.5% for different subsets relative to the entire set of breeds, while the loss of founder genome equivalents ranged from 22.9% to 39.3%.

A genetic background for reintroduction program of the European bison ( Bison bonasus) in the Carpathians

The European bison, extirpated from the Carpathian Mountains over 200 years ago, was reintroduced to the Bieszczady Mountains in the 1960/1970s in two small, isolated herds, and is now threatened by high inbreeding and low genetic variability. A new program of re-establishing viable populations in the Carpathians is based on the genetic analysis of formerly released animals, using the European Bison Pedigree Book. Calculating founder contributions, founder genome survival, founder genome equivalent, inbreeding coefficient and mean kinship allows the identification of under-represented or missing founders. Since genetic variability is much higher among bison in captivity and, in Poland, the Lowland–Caucasian line is represented only in those free-ranging herds, the reintroduction will be based on animals from foreign breeding centres. Bison will be released into existing herds, and planned new introduction sites, to facilitate natural gene exchange in the future. The same approach will be recommended for planned introductions in the Slovakian and Romanian Carpathians.

Assessing the contribution of breeds to genetic diversity in conservation schemes.

The quantitative assessment of genetic diversity within and between populations is important for decision making in genetic conservation plans. In this paper we define the genetic diversity of a set of populations, S, as the maximum genetic variance that can be obtained in a random mating population that is bred from the set of populations S. First we calculated the relative contribution of populations to a core set of populations in which the overlap of genetic diversity was minimised. This implies that the mean kinship in the core set should be minimal. The above definition of diversity differs from Weitzman diversity in that it attempts to conserve the founder population (and thus minimises the loss of alleles), whereas Weitzman diversity favours the conservation of many inbred lines. The former is preferred in species where inbred lines suffer from inbreeding depression. The application of the method is illustrated by an example involving 45 Dutch poultry breeds. The calculations used were easy to implement and not computer intensive. The method gave a ranking of breeds according to their contributions to genetic diversity. Losses in genetic diversity ranged from 2.1% to 4.5% for different subsets relative to the entire set of breeds, while the loss of founder genome equivalents ranged from 22.9% to 39.3%.

The conservation role of captive African wild dogs ( Lycaon pictus)

Since 1954, several southern African institutions have established captive breeding programs to ensure the long-term survival of the African wild dog ( Lycaon pictus). To aid this, a studbook was assembled to provide genetic and demographic information for the southern African captive populations, comprising the largest existing regional population of captive African wild dogs. These populations were investigated over three time frames: during 1985–1990, during 1991–1996 and populations alive in January 1997. The captive-breeding programme is successful with a positive population growth, a significant lowering of inbreeding and mean kinship and an increased genetic diversity. However, genetic variability levels appear lower and levels of inbreeding appear higher compared with wild populations. In addition, there have been no successful long-term re-introductions into the southern African wild using captive-bred dogs, mainly due to the lack of close collaboration between captive breeding and nature conservation institutions. The ultimate success of a conservation programme not only depends on proper demographic and genetic management of the captive population, but primarily on the successful collaboration of all scientific, captive breeding and conservation agencies involved.

Unpedigreed populations and worst‐case scenarios

AbstractA population in which parentage information is not recorded is considered a pedigree “black hole” in terms of genetic management. Integration of animals from such an unpedigreed population into a genetically managed population is often accomplished by assuming a worst‐case scenario and recording all animals as highly interrelated (e.g., full siblings). The assumption that a worst‐case scenario is appropriate under a wide variety of circumstances is evaluated. It was determined that the genetic costs of overestimating relationships among animals from an unpedigreed population are always greater than the genetic costs of underestimating relationships by the same amount. This demonstrates that worst‐case scenarios, which are by definition intentional overestimates, are not generally appropriate. A method of obtaining an estimate that will yield the lowest overall genetic cost using the possible maximum and minimum levels of relatedness among animals from the unpedigreed population is presented along with two methods for implementation. Finally, for cases in which the estimated average relatedness among animals from an unpedigreed population is low, it is recommended that different analytical studbook datasets be used for calculation of inbreeding coefficients and mean kinship coefficients. This strategy would allow close estimation of average relatedness without risking inadvertent pairing of highly related animals from the unpedigreed population. Zoo Biol 20:305–314, 2001. © 2001 Wiley‐Liss, Inc.

A study of inbreeding and kinship in intracranial aneurysms in the Saguenay Lac-Saint-Jean region (Quebec, Canada).

The genealogies of 533 individuals with an intracranial aneurysm (IA) born in the Saguenay-Lac-Saint-Jean region, a geographically isolated area located in northeastern Quebec, were reconstructed using a population-based register. A control group consisting of three individuals of the same sex and born on the same day and in the same municipality than the IA patients was created; the genealogies of the 1599 controls were also reconstructed. The coefficients of inbreeding and kinship were calculated. Familial aggregation, i.e. the presence of IA in two or more first- to third-degree relatives, was also sought. The mean inbreeding coefficient was lower in the IA group than in the control group (7.92 x 10(-4) versus 10.04 x 10(-4)). The mean kinship coefficient was higher in the IA group than in the control group (2.17 x 10(-4) versus 1.55 x 10(-4)). Forty-eight IA patients (9.0%) were first-degree relatives compared to only 1.9% of the control individuals. The proportion of individuals showing familial aggregation was higher in the IA group than in the control group (29.8% and 18.6% respectively). These results strongly suggest that some IA are genetically determined in this population.

Genealogy and geographical distribution of CFTR mutations in Saguenay Lac-Saint-Jean (Quebec, Canada).

Saguenay Lac-Saint-Jean (SLSJ), a region located in northeastern Quebec, has a high incidence of cystic fibrosis (CF). During the past few years the majority of the CF patients have been genotyped. The geographical distribution of the birth places of the patients and obligate carriers of the 621 + 1G-->T, the A455E and the delta F508 mutations (which accounted for 89% of the CF chromosomes) showed differences that can be explained by some degree of isolation but also by differential migration. The mean inbreeding and kinship coefficients were higher among the various CFTR mutation groups than in the general population. An ancestor couple common to most of the A455E carriers was identified. These data further substantiate the role of founder effect in the CF population of SLSJ.

Selective Breeding Programs for Rare Alleles: Examples from the Przewalski's Horse and California Condor Pedigrees.

As extinction due to loss of habitat grows more imminent for a wide variety of species, population management has been recognized as an important means toward species survival and recovery in the wild. Genetic management practices generally seek to preserve population variation at the level of the genome. It has been proposed, however, that such efforts should instead be directed to specific loci barboring alleles with particular selective benefits. This strategy may in fact result in greater loss of variation in the rest of the genome, potentially threatening population viability. Pedigrees of Przewalski's horse (Equus prezewalskii) and the California Condor (Gymnogyps californianus) were used to evaluate a "rare kinship" management strategy in which a single individual known to carry a unique allele is repeatedly bred to mates chosen by mean kinship in order to increase the frequency of the rare allele. This strategy led to increased population mean kinship and reduced gene diversity and founder genome equivalents relative to a no-management control pedigree and performed considerably worse than a pedigree managed for mean kinship. Reduced success in the breeding program can be directly attributed to significant deviations of founders' representations from their respective target values. As a result, a strategy for increasing the frequency of rare alleles cannot be generally recommended for management of captive populations. Under strict conditions; however, limited use of this strategy may be applicable only if used for a short time under careful monitoring by pedigree analysis. Even if these conditions are met, managing by a more conventional method such as mean kinship is preferable. These results illustrate the utility of thoughtful analysis of pedigree information to successful population management. Programas de cría selectivos para alelos raros: Ejemplos de los pedigrés de los caballos de Przewalski y de los condores de California.