Population improvement in lucerne (Medicago sativa L.): components of inbreeding depression are different in original and improved populations

1998 ◽  
Vol 38 (8) ◽  
pp. 831 ◽  
Author(s):  
C. A. Kimbeng ◽  
E. T. Bingham
Keyword(s):  
Inbreeding Depression ◽  
Chromosome Doubling ◽  
Genetic Load ◽  
Field Trials ◽  
Improvement Strategy ◽  
Improvement Program ◽  
Original Population ◽  
Deleterious Alleles ◽  
Herbage Yield ◽  
Population Improvement

Summary. Inbreeding depression, the lowered fitness of inbred individuals compared with their non-inbred counterparts, is an important concept in lucerne improvement; but is poorly understood. Two-allele autotetraploid populations are suitable for studying inbreeding depression, especially when the population improvement strategy involves inbreeding, because they are derived from chromosome-doubling of hybrid diploid plants. They have a maximum of 2 alleles and a single allelic interaction per locus. Inbreeding depression was compared in original 2-allele autotetraploid populations and populations that had undergone inbreeding and selection. The original and improved (selected) populations were produced by intercrossing 2 single-cross lines from the original and improved 2-allele autotetraploid populations respectively. Herbage yield of the S1 and intercrossed generations derived from these populations was evaluated in field trials at Arlington, Wisconsin, USA, and used to estimate inbreeding depression. Herbage yield of the S1 and intercrossed generations derived from the improved population were significantly (P<0.01) higher, by 13.3 and 24%, respectively, than those derived from the original population. Selection during inbreeding probably decreased the frequency of deleterious alleles and accumulated favourable alleles. Inbreeding depression values were higher in the improved compared with the original population. Genetic load of deleterious alleles may account for much of the inbreeding depression observed in the original population, whereas, in the improved population, loss of heterozygosity or non-additive gene interactions between favourable alleles on linked chromosome segments may account for the substantial inbreeding depression. Therefore, in a population improvement program, the causes of inbreeding depression seem to be more important than their estimated value.

Effect of inbreeding on growth of white clover

2006 ◽  
Vol 12 ◽  
pp. 131-134
Author(s):  
Greig Cousins ◽  
Derek Woodfield
Keyword(s):  
Inbreeding Depression ◽  
White Clover ◽  
Yield Reduction ◽  
Breeding Strategies ◽  
S Locus ◽  
Sheep Grazing ◽  
Herbage Yield ◽  
Population Improvement ◽  
The Impact ◽  
Future Population

Determining the impact of inbreeding on white clover growth will assist in determining the optimal breeding strategies for future population improvement. A dominant self-fertility allele (Sf) at the S locus was used to inbreed white clover to nearhomozygosity (F=0.99). Inbreeding depression was higher in the glasshouse experiment than was observed under sheep grazing in the field. It was also higher for comparable generations with a 54% reduction in herbage yield of the S1 generation in the glasshouse compared with 29% yield reduction under grazing. The level of inbreeding depression for herbage yield of the S1 and S2 generations observed in the glasshouse were consistent with the theoretical reduction in yield. However in later generations the actual herbage yield was consistently higher than expected. This may be due to heterozygosity being maintained during inbreeding or to the elimination of weaker individuals under higher competition and grazing experienced under field conditions. The degree to which inbreeding depression is overcome by outcrossing (heterosis) in white clover will determine whether hybrids or semi-hybrid cultivars can be successfully developed

scholarly journals Inbreeding Depression in Small Populations of Self-Incompatible Plants

Genetics ◽  
2001 ◽  
Vol 159 (3) ◽  
pp. 1217-1229
Author(s):  
Sylvain Glémin ◽  
Thomas Bataillon ◽  
Joëlle Ronfort ◽  
Agnès Mignot ◽  
Isabelle Olivieri
Keyword(s):  
Inbreeding Depression ◽  
Genetic Load ◽  
Joint Effect ◽  
Breeding Systems ◽  
Small Populations ◽  
S Locus ◽  
Frequency Dependent ◽  
Frequency Dependent Selection ◽  
Deleterious Alleles ◽  
Negative Frequency Dependent Selection

Abstract Self-incompatibility (SI) is a widespread mechanism that prevents inbreeding in flowering plants. In many species, SI is controlled by a single locus (the S locus) where numerous alleles are maintained by negative frequency-dependent selection. Inbreeding depression, the decline in fitness of selfed individuals compared to outcrossed ones, is an essential factor in the evolution of SI systems. Conversely, breeding systems influence levels of inbreeding depression. Little is known about the joint effect of SI and drift on inbreeding depression. Here we studied, using a two-locus model, the effect of SI (frequency-dependent selection) on a locus subject to recurrent deleterious mutations causing inbreeding depression. Simulations were performed to assess the effect of population size and linkage between the two loci on the level of inbreeding depression and genetic load. We show that the sheltering of deleterious alleles linked to the S locus strengthens inbreeding depression in small populations. We discuss the implications of our results for the evolution of SI systems.

scholarly journals Recent approaches into the genetic basis of inbreeding depression in plants

2003 ◽  
Vol 358 (1434) ◽  
pp. 1071-1084 ◽  
Author(s):  
David E. Carr ◽  
Michele R. Dudash
Keyword(s):  
Inbreeding Depression ◽  
Genetic Basis ◽  
Genetic Load ◽  
Strong Support ◽  
Major Effect ◽  
Inbred Lines ◽  
Recessive Mutations ◽  
Deleterious Alleles ◽  
Experimental Approaches ◽  
Marker Segregation Distortion

Predictions for the evolution of mating systems and genetic load vary, depending on the genetic basis of inbreeding depression (dominance versus overdominance, epistasis and the relative frequencies of genes of large and small effect). A distinction between the dominance and overdominance hypotheses is that deleterious recessive mutations should be purged in inbreeding populations. Comparative studies of populations differing in their level of inbreeding and experimental approaches that allow selection among inbred lines support this prediction. More direct biometric approaches provide strong support for the importance of partly recessive deleterious alleles. Investigators using molecular markers to study quantitative trait loci (QTL) often find support for overdominance, though pseudo–overdominance (deleterious alleles linked in repulsion) may bias this perception. QTL and biometric studies of inbred lines often find evidence for epistasis, which may also contribute to the perception of overdominance, though this may be because of the divergent lines initially crossed in QTL studies. Studies of marker segregation distortion commonly uncover genes of major effect on viability, but these have only minor contributions to inbreeding depression. Although considerable progress has been made in understanding the genetic basis of inbreeding depression, we feel that all three aspects merit more study in natural plant populations.

Population improvement in lucerne (Medicago sativa L.): genetic analyses in original and improved populations

1999 ◽  
Vol 39 (5) ◽  
pp. 549 ◽  
Author(s):  
C. A. Kimbeng ◽  
E. T. Bingham
Keyword(s):  
Quantitative Genetics ◽  
Genetic Load ◽  
Gene Interaction ◽  
Forage Yield ◽  
Fourth Degree ◽  
Repulsion Phase ◽  
Deleterious Alleles ◽  
Medicago Sativa L ◽  
Population Improvement ◽  
Population Interaction

Most quantitative genetics analyses are limited to the first (mean) and second (variance) degree statistics and their derivatives. Analyses based on third (skewness) and fourth (kurtosis) degree statistics can be useful especially for detecting and characterising the nature of gene interactions. Third and fourth degree statistics were analysed and used to interpret differences in forage yield among S1 families of lucerne derived from double-cross populations that were synthesised before (OGDC) and after (AGDC) improvement via inbreeding and selection. Higher levels of genetic load (deleterious alleles) were revealed in the OGDC population compared with the improved population. The analyses also revealed the importance of gene interaction for forage yield in lucerne. In the unselected OGDC population, interaction between alleles in repulsion phase linkages was more important, whereas, in the selected AGDC population, interaction between alleles linked in coupling phase assumed greater importance. The above results suggest that inbreeding and selection in lucerne can accumulate favourable alleles over generations of selection and result in population improvement. Skewness and kurtosis are relatively easy to compute and interpret and should serve as valuable tools in tetraploid quantitative genetics analyses.

scholarly journals Selection, Load and Inbreeding Depression in a Large Metapopulation

Genetics ◽  
2002 ◽  
Vol 160 (3) ◽  
pp. 1191-1202 ◽  
Author(s):  
Michael C Whitlock
Keyword(s):  
Population Structure ◽  
Inbreeding Depression ◽  
Population Subdivision ◽  
Response To Selection ◽  
Mutation Load ◽  
Deleterious Alleles ◽  
Subdivided Population ◽  
Soft Selection ◽  
Mean Fitness ◽  
The Mean

Abstract The subdivision of a species into local populations causes its response to selection to change, even if selection is uniform across space. Population structure increases the frequency of homozygotes and therefore makes selection on homozygous effects more effective. However, population subdivision can increase the probability of competition among relatives, which may reduce the efficacy of selection. As a result, the response to selection can be either increased or decreased in a subdivided population relative to an undivided one, depending on the dominance coefficient FST and whether selection is hard or soft. Realistic levels of population structure tend to reduce the mean frequency of deleterious alleles. The mutation load tends to be decreased in a subdivided population for recessive alleles, as does the expected inbreeding depression. The magnitude of the effects of population subdivision tends to be greatest in species with hard selection rather than soft selection. Population structure can play an important role in determining the mean fitness of populations at equilibrium between mutation and selection.

Inbreeding depression in two field trials of young pinus sylvestris (L.)

1987 ◽  
Vol 2 (1-4) ◽  
pp. 281-290 ◽  
Author(s):  
Kenneth Lundkvist ◽  
Gösta Eriksson ◽  
Lennart Norell ◽  
Inger Ekberg
Keyword(s):  
Pinus Sylvestris ◽  
Inbreeding Depression ◽  
Field Trials

scholarly journals Yield evaluation of varieties from the world collection of birdsfoot trefoil (Lotus corniculatus L.)

2011 ◽  
Vol 48 (No. 6) ◽  
pp. 265-270
Author(s):  
J. Pelikán
Keyword(s):  
Seed Yield ◽  
Lotus Corniculatus ◽  
Field Trials ◽  
Birdsfoot Trefoil ◽  
Local Varieties ◽  
World Collection ◽  
The World ◽  
Herbage Yield ◽  
Second Year ◽  
Good Productivity

In field trials in 1998&ndash;2000, ten varieties of the world collection of birdsfoot trefoil (Lotus corniculatus) were evaluated for herbage and hay yields. In all the years of testing yields from three cuttings and total annual production were evaluated. In 1999, seed yield was also recorded. As a&nbsp;control, alfalfa (Medicago sativa) variety was included in the experiment. The test varieties showed good productivity in the first and especially in the second year of testing, most of them exceeded alfalfa in herbage yield in individual cuttings and in total productions. As for hay yield, the differences were not so great. Local varieties showed very good productivity, predominantly in herbage yields. Of foreign varieties, the best herbage, hay and seed yielder was the Hungarian variety Puszta. There were no statistical differences in seed yield between the varieties. The yields were, however, relatively low.

Genetic load and biological changes to extant humans

2020 ◽  
pp. 1-4
Author(s):  
Arthur Saniotis ◽  
Maciej Henneberg ◽  
Kazhaleh Mohammadi
Keyword(s):  
Natural Selection ◽  
Current Knowledge ◽  
Genetic Load ◽  
Differential Fertility ◽  
Medical Interventions ◽  
Deleterious Alleles ◽  
Gradual Process ◽  
Genetic Complexity ◽  
Sexual Recombination ◽  
Improved Sanitation

Abstract Extant humans are currently increasing their genetic load, which is informing present and future human microevolution. This has been a gradual process that has been rising over the last centuries as a consequence of improved sanitation, nutritional improvements, advancements in microbiology and medical interventions, which have relaxed natural selection. Moreover, a reduction in infant and child mortality and changing societal attitudes towards fertility have led to a decrease in total fertility rates (TFRs) since the 19th century. Generally speaking, decreases in differential fertility and mortality have meant that there is less opportunity for natural selection to eliminate deleterious mutations from the human gene pool. It has been argued that the average human may carry ~250–300 mutations that are mostly deleterious, as well as several hundred less-deleterious variants. These deleterious alleles in extant humans mean that our fitness is being constrained. While such alleles are viewed as reducing human fitness, they may also have had an adaptive function in the past, such as assisting in genetic complexity, sexual recombination and diploidy. Saying this, our current knowledge on these fitness compromising alleles is still lacking.

scholarly journals Inbreeding depression due to mildly deleterious mutations in finite populations: size does matter

2000 ◽  
Vol 75 (1) ◽  
pp. 75-81 ◽  
Author(s):  
THOMAS BATAILLON ◽  
MARK KIRKPATRICK
Keyword(s):  
Population Size ◽  
Inbreeding Depression ◽  
Deleterious Mutation ◽  
Large Population ◽  
Genetic Load ◽  
Breeding Systems ◽  
Deleterious Mutations ◽  
Single Locus Analysis ◽  
Population Sizes ◽  
Inbreeding Rate

We studied the effects of population size on the inbreeding depression and genetic load caused by deleterious mutations at a single locus. Analysis shows how the inbreeding depression decreases as population size becomes smaller and/or the rate of inbreeding increases. This pattern contrasts with that for the load, which increases as population size becomes smaller but decreases as inbreeding rate goes up. The depression and load both approach asymptotic limits when the population size becomes very large or very small. Numerical results show that the transition between the small and the large population regimes is quite rapid, and occurs largely over a range of population sizes that vary by a factor of 10. The effects of drift on inbreeding depression may bias some estimates of the genomic rate of deleterious mutation. These effects could also be important in the evolution of breeding systems in hermaphroditic organisms and in the conservation of endangered populations.

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