Cycles Of Reciprocal Recurrent Selection Research Articles

Molecular characterization of doubled haploid lines derived from different cycles of the Iowa Stiff Stalk Synthetic (BSSS) maize population.

Molecular characterization of a given set of maize germplasm could be useful for understanding the use of the assembled germplasm for further improvement in a breeding program, such as analyzing genetic diversity, selecting a parental line, assigning heterotic groups, creating a core set of germplasm and/or performing association analysis for traits of interest. In this study, we used single nucleotide polymorphism (SNP) markers to assess the genetic variability in a set of doubled haploid (DH) lines derived from the unselected Iowa Stiff Stalk Synthetic (BSSS) maize population, denoted as C0 (BSSS(R)C0), the seventeenth cycle of reciprocal recurrent selection in BSSS (BSSS(R)C17), denoted as C17 and the cross between BSSS(R)C0 and BSSS(R)C17 denoted as C0/C17. With the aim to explore if we have potentially lost diversity from C0 to C17 derived DH lines and observe whether useful genetic variation in C0 was left behind during the selection process since C0 could be a reservoir of genetic diversity that could be untapped using DH technology. Additionally, we quantify the contribution of the BSSS progenitors in each set of DH lines. The molecular characterization analysis confirmed the apparent separation and the loss of genetic variability from C0 to C17 through the recurrent selection process. Which was observed by the degree of differentiation between the C0_DHL versus C17_DHL groups by Wright's F-statistics (FST). Similarly for the population structure based on principal component analysis (PCA) revealed a clear separation among groups of DH lines. Some of the progenitors had a higher genetic contribution in C0 compared with C0/C17 and C17 derived DH lines. Although genetic drift can explain most of the genetic structure genome-wide, phenotypic data provide evidence that selection has altered favorable allele frequencies in the BSSS maize population through the reciprocal recurrent selection program.

Number of progenies and repetitions for reciprocal full-sib recurrent selection programs in maize

ABSTRACT For a reciprocal recurrent selection (RRS) program to succeed, it is essential to maintain genetic variability throughout the selection cycles and to obtain accurate estimates of genetic parameters, which in turn are directly related to the number of progenies and repetitions evaluated. This study evaluates the potential of maize progenies of the sixth cycle of RRS and proposes, using simulation methods, the ideal combination of the number of progenies and repetitions to employ in reciprocal full-sib recurrent selection. A total of 163 full-sib progenies were evaluated in a randomized block design with six repetitions. Based on the yield data, analysis of variance was carried out, and different scenarios were simulated using the Monte Carlo chain method. These scenarios varied in the number of repetitions (two, four, and six) and progenies (30 to 163). The contrast between progenies and controls was significant, revealing the potential of the progenies of the sixth cycle of RRS. The high magnitude of the selective accuracy (0.77) was reflected in high estimates of heritability, which allowed for efficient phenotypic selection, obtaining selection gains of 14.07%. From the estimates of phenotypic and genotypic variance, heritability, accuracy, and standard error, it was found that a repetition number above two results in drastic changes in the estimates of these parameters; however, with the use of 130 progenies, these estimates tend to stabilize, implying that a high number of progenies does not interfere decisively in the quality of most parameters, except for the limits of maximum and minimum variation.

Genetic Gains to Grain Yield of Maize Varieties for Small Farmers in Brazil

The demand for expanding the genetic base in working collections of older maize breeding programs points to the need to pool efforts and reaffirm methodologies for conserving genetic variability that can still be accessed in maize populations. The objective of the work was to select full sib maize progenies and to estimate genetic gains in the first cycle of reciprocal recurrent selection for common maize intended for cultivation in a region characterized by family farm, in Brazil. We evaluated 120 full sib families of maize from crossbreeding between individuals of the Cimmyt and Piranão varieties. Competition trials were conducted at two experimental stations in the state of Espírito Santo, Brazil. A randomized block design was adopted with 2 repetitions, arranged in sets. Different selection indexes were tested in order to enhance gains in productivity and prolificacy. The selection of 40 superior families made it possible to estimate a gain of 0.77 Mg ha-1 in grain productivity for producers in the region. With these results, we discussed the importance of work to improve maize populations for small producers to motivate the conservation of the genetic variability of tropical maize germplasm. Thus, from the results obtained in this study, we show the possibility of investing in technologies aimed at small producers in order to motive the conservation of genetic resources, food sovereignty of producers and, consequently, world security, given the importance of this culture for human feed.

Genetic progress in maize from advanced cycles of reciprocal recurrent selection through REML/BLUP

Breeding methods such as reciprocal recurrent selection (RRS) is very important alternative to breeders. This strategy, besides allowing continuous genetic progress, helps maintaining the genetic variability of populations. The aim of the present study was to estimate genetic parameters, as well as to predict selection gains in advanced cycles of reciprocal recurrent selection of maize progenies through mixed models. Two selection cycles were considered. We evaluated 196 and 169 progenies in the 15 and 16 cycles, respectively. The yield potential of the progenies was evaluated from the following characteristics: grain yield, number of ears, weight of ears and weight of 100 seeds. The estimate of variance components and the prediction of genetic values were based on the REML/BLUP method. Overall, the genetic parameters were increased in the 16th cycle estimates compared to the previous cycle. It is worth highlighting that heritability coefficient for the grain yield was (0.81) in the 16th cycle, since it resulted in 21% of selection gain. Results showed that, even after sixteen recurrent selection cycles, the populations under selection have high potential for satisfactory genetic gains.

In silico simulation of future hybrid performance to evaluate heterotic pool formation in a self-pollinating crop

Hybrid vigour has the potential to substantially increase the yield of self-pollinating crops such as wheat and rice, but future hybrid performance may depend on the initial strategy to form heterotic pools. We used in silico stochastic simulation of future hybrid performance in a self-pollinating crop to evaluate three strategies of forming heterotic pools in the founder population. The model included either 500, 2000 or 8000 quantitative trait nucleotides (QTN) across 10 chromosomes that contributed to a quantitative trait with population mean 100 and variance 10. The average degree of dominance at each QTN was either 0.2, 0.4 or 0.8 with variance 0.2. Three strategies for splitting the founder population into two heterotic pools were compared: (i) random split; (ii) split based on genetic distance according to principal component analysis of SNP genotypes; and (iii) optimized split based on F1 hybrid performance in a diallel cross among the founders. Future hybrid performance was stochastically simulated over 30 cycles of reciprocal recurrent selection based on true genetic values for additive and dominance effects. The three strategies of forming heterotic pools produced similar future hybrid performance, and superior future hybrids to a control population selected on inbred line performance when the number of quantitative trait nucleotides was ≥2000 and/or the average degree of dominance was ≥0.4.

Changes in heterosis of maize (Zea mays L.) varietal cross hybrids after four cycles of reciprocal recurrent selection

Two improved tropical maize composites, TZL COMP3 and TZL COMP4; representing complementary heterotic pools have been subjected to four cycles of reciprocal recurrent selection (RRS) for two decades to enhance varietal cross performance. The objectives of this study were to evaluate the effect of selection on genetic gain in heterosis for grain yield and other agronomic traits of these composites. Ten parental populations representing the C0 to C4 of each composite and their crosses plus a varietal check were evaluated in a trial at eight environments in Nigeria. Grain yield of the varietal crosses increased with selection by 3.1% cycle–1. Mean grain yields of the C4 × C4 varietal cross exceeded that of a popular improved reference variety by 23%. Selection also reduced anthesis-silking interval, improved ear characteristics, phenotypic appeal and resistance to foliar diseases. Mid-parent heterosis (MPH) increased from 4% at C0 × C0 to 24% at C4 × C4. The average rate of genetic gain in heterosis for grain yield in population crosses was 3.1% possibly because of presence of non-additive gene effects. The results of our study present the potential usefulness of the advanced selection cycle as sources of diverse inbred lines with improved combining ability as well as improved varietal crosses that can be multiplied and deployed in areas with limited market access.

‘UENF 506-11’: a new maize cultivar for the North and Northwest of Rio de Janeiro State

Abstract The intervarietal hybrid ‘UENF 506-11’ was derived from full-sib maize families in the 11th cycle of reciprocal recurrent selection. It produces a grain yield of 7.57 tons ha-1, and is recommended for cultivation in the North and Northwest regions of the Rio de Janeiro State.

Genetic Advance in Grain Yield and Other Traits in Two Tropical Maize Composites Developed via Reciprocal Recurrent Selection

Assessment of genetic gain in two tropical maize (Zea mays L.) composites improved across years is critical in determining their future improvement and use as sources of inbred lines. Two genetically complementary tropical maize composites were subjected to four cycles of reciprocal recurrent selection (RRS) for grain yield, resistance to foliar diseases, and other desirable agronomic traits using a reciprocal S1 testcross evaluation scheme. The objectives of this study were to evaluate the effects of this selection scheme on: (i) the rate of genetic gain in grain yield and other traits, (ii) the changes in variance and heritability estimates, and (iii) changes in correlations between grain yield and other traits in the two tropical maize composites. One hundred S1 lines, each derived from the original (C0) and advanced (C4) cycles of the two composites, were crossed in pairs to form 100 C0 × C0 and 100 C4 × C4 testcrosses, which were evaluated along with 10 commercial hybrid checks in a replicated trial across eight environments in Nigeria. The observed genetic gain was 3.60% cycle−1 for grain yield. On average, the top 10 C4 × C4 testcrosses outyielded the commercial hybrids by 29% and had desirable agronomic traits and improved resistance to foliar diseases. The genetic variance estimates for C0 and C4 of each composite were significantly larger than zero for most traits. These results indicated that the RRS was effective in improving grain yield and other desirable agronomic traits without diminishing genetic variability that can be exploited for further improvement of the two tropical maize composites.

Genetic divergence in two tropical maize composites after four cycles of reciprocal recurrent selection

AbstractTwo tropical maize composites were subjected to four cycles of reciprocal recurrent selection to develop divergent inbred lines with good combining ability. This study was conducted to examine the extent of genetic diversity, changes in allele composition and genetic structure, of 100 randomly selected S1 lines each from the original (C0) and advanced (C4) selection cycles of TZL COMP3 and TZL COMP4, genotyped using single nucleotide polymorphism (SNP) markers. Results revealed that the proportion of alleles at both low and high frequencies decreased from C0 to C4, whereas those at intermediate frequencies increased at C4 in the two composites. More unique and other alleles were lost at C4 in TZL COMP3 relative to those in TZL COMP4. The changes in different measures of genetic diversity were either small or negligible with selection in the two composites. The proportion of markers departing from Hardy–Weinberg equilibrium (HWE) decreased with selection, whereas the total number of pairs of markers in linkage disequilibrium increased with selection in the two composites. Examination of changes in population structures using a model‐based approach as well as cluster and multivariate analyses found a high degree of concordance in stratifying the 400 S1 lines into four non‐overlapping groups corresponding to the two selection cycles each within the reciprocal composites. The observed molecular‐based divergence between cycles within the same composite and the clear differentiation between the complementary composites highlight the importance of reciprocal recurrent selection for preserving genetic diversity for long‐term selection. This increases the potential of the advanced selection cycles to sustain genetic gain in productivity of hybrids adapted to the savannas in West and Central Africa.

Evaluation of progenies from the fifth reciprocal recurrent selection cycle in maize.

The objective of this study was to evaluate the performance of 119 full sib progenies of the fifth cycle of reciprocal recurrent selection (RRS) derived from of Universidade Federal de Lavras maize breeding program. The experiment was carried out in an 11 x 11 triple lattice design at two locations (Lavras, Lambari). The plots consisted of two rows of 3 m, with four plants per 1 m and 0.60 meters of spacing between lines. The grain yield was obtained as kg/plot through weighing of husked ears. The contrast between progenies and controls was not significant, indicating there were no significant differences among the average grain yields of the progenies and controls. When considering the joint analysis, heritability was 64.2%; however, this estimate did not differ from the values estimated for each location separately. Estimates of genetic and phenotypic variance among progenies ranged from 0.21 to 0.28 and 0.30 to 0.47, respectively. Estimates of selection gain, for 10% selection intensity, indicated gains of 16% in the joint analysis of the two locations. The progenies of the fifth cycle of RRS had high average grain yield, associated with high variability. In comparison to the average grain yields exhibited by the controls, it was concluded that the progenies have the potential to be commercially exploited.

Functional molecular markers (EST-SSR) in the full-sib reciprocal recurrent selection program of maize (Zea mays L.).

This study aimed to improve grain yield in the full-sib reciprocal recurrent selection program of maize from the North Fluminense State University. In the current phase of the program, the goal is to maintain, or even increase, the genetic variability within and among populations, in order to increase heterosis of the 13th cycle of reciprocal recurrent selection. Microsatellite expressed sequence tags (EST-SSRs) were used as a tool to assist the maximization step of genetic variability, targeting the functional genome. Eighty S1 progenies of the 13th recur-rent selection cycle, 40 from each population (CIMMYT and Piranão), were analyzed using 20 EST-SSR loci. Genetic diversity, observed heterozygosity, information content of polymorphism, and inbreeding co-efficient were estimated. Subsequently, analysis of genetic dissimilarity, molecular variance, and a graphical dispersion of genotypes were conducted. The number of alleles in the CIMMYT population ranged from 1 to 6, while in the Piranão population the range was from 2 to 8, with a mean of 3.65 and 4.35, respectively. As evidenced by the number of alleles, the Shannon index showed greater diversity for the Piranão population (1.04) in relation to the CIMMYT population (0.89). The genic SSR markers were effective in clustering genotypes into their respective populations before selection and an increase in the variation between populations after selection was observed. The results indicate that the study populations have expressive genetic diversity, which cor-responds to the functional genome, indicating that this strategy may contribute to genetic gain, especially in association with the grain yield of future hybrids.

Estimates for genetic variance components in reciprocal recurrent selection in populations derived from maize single-cross hybrids.

This study was carried out to obtain the estimates of genetic variance and covariance components related to intra- and interpopulation in the original populations (C0) and in the third cycle (C3) of reciprocal recurrent selection (RRS) which allows breeders to define the best breeding strategy. For that purpose, the half-sib progenies of intrapopulation (P11 and P22) and interpopulation (P12 and P21) from populations 1 and 2 derived from single-cross hybrids in the 0 and 3 cycles of the reciprocal recurrent selection program were used. The intra- and interpopulation progenies were evaluated in a 10 × 10 triple lattice design in two separate locations. The data for unhusked ear weight (ear weight without husk) and plant height were collected. All genetic variance and covariance components were estimated from the expected mean squares. The breakdown of additive variance into intrapopulation and interpopulation additive deviations (σ τ 2) and the covariance between these and their intrapopulation additive effects (CovAτ) found predominance of the dominance effect for unhusked ear weight. Plant height for these components shows that the intrapopulation additive effect explains most of the variation. Estimates for intrapopulation and interpopulation additive genetic variances confirm that populations derived from single-cross hybrids have potential for recurrent selection programs.

Effect of Selection on Amylose and Amylopectin Concentration in Maize (<i>Zea mays</i> L.)

Two cycles of reciprocal recurrent selection at the University of Nigeria, Nsukka shifted the average percentage amylopectin of the eight populations of maize (Zea mays L.) from 74.50 to 81.30 per cent, 74.00 to 82.00 percent , 77.50 to 82.50 percent, 76.00 to 82.00 percent, 77.00 to 82.5 per cent, 74.50 to 82.05 per cent, 75.50 to 82.30 per cent and from 77.00 to 82.32 percent. Selection was not effective in developing high amylose strain. The average percentage amylose of the eight populations of maize decreased from 25.50 to 20.00 percent, 26.00 to 19.30 percent,22.50 to 20.00 percent, 24.00 to 20.10 percent, 23.00 to 19.31 percent, 25.50 to 19.40 percent, 24.50 to 20.41 percent, and 23.00 to 19.23 percent. The developed synthetics can be used as commercial varieties per se, as reservoirs of germplasm for further improvement, and for the extraction of superior inbred lines for use in hybrid maize production.Key words: Reciprocal Recurrent Selection, Amylopectin, Amylose, Maize synthetics, Germplasm

Development of High Protein Populations of Maize (Zea mays L.) From Three Cycles of Reciprocal Recurrent Selection

This breeding programme was initiated at the Department of Crop Production and Landscape Management's teaching and research farm of the Ebonyi State University, Abakaliki. The genetic materials were sourced from the University of Nigeria gene bank. After three cycles of reciprocal recurrent selection, two high protein populations of maize (Zea mays L.) with mean protein content estimates of 14.4 Nsukka High Protein - Early (NHP-E) and 14.3 Nsukka High Protein - Late (NHP-L) were developed from populations with average protein contents of 7.6 and 8.6 per cent, respectively. The new populations can be used as commercial varieties, as parents in varietal crosses or as reservoirs of germplasm for further improvement and extraction of superior inbred lines for use in hybrid maize production.

Increase In Protein, Oil, Amylose and Amylopectin Contents of Two Populations of Maize (Zea Mays L.) After Two Cycles of Reciprocal Recurrent Selection

This research was conducted at the teaching and research farm of the Department of Crop Production and Landscape Management, Ebonyi State University, Abakaliki, from 2006 to 2012 cropping seasons to develop maize populations of increase protein, oil, amylose and amylopectin contents. Total of eight (8) maize varieties were used for the study and were grouped into two populations, A and B. Population A was coded A 1 , A 2 , A 3 and A 4 while population B was coded B 1 , B 2 , B 3 and B 4 . These two populations were genetically variable based on the time of maturity, percentage protein, oil, amylose and amylopectin. The mean protein content of the parents was 8.74% while their progenies after second cycle had percentage protein content of 13.27%, showing an increase of 4.53% with mid parent heterosis of 52%. The oil content of the open-pollinated maize varieties was pushed towards increasing order from 6.19% for population A and 4.19% for population B of the original populations to 5.61% and 5.62% for populations A and B respectively of the first cycle populations. These were further pushed up to 8.08% and 8.46% of the second cycle populations A and B respectively. The mean amylose content of the original population was 24.25% and the mean amylose content of the progenies after the first cycle was 22.02%. The second cycle synthetics had mean amylose content of 19.72%, showing a decrease of 4.53%. The mid parent heterosis was -9.2%. The mean amylopectin content of the original population was 75.75% and the mean amylopectin content of the selected high amylopectin was 82.13%, showing an increase of 6.38% over the mean amylopectin content of the original population. The breeding programme seems to be very effective in improving both the high, medium and low protein, oil, amylose and amylopectin contents of the original maize populations to all high protein, oil and amylopectin contents, except amylose, after the second cycle. In all, this method offers definite promise. Further progress in improving chemical constituents as well as other characters is theoretically possible in future cycles.

Full-sib reciprocal recurrent selection in the maize populations Cimmyt and Piranão

We estimated the genetic gains of the 12th cycle of reciprocal recurrent selection for maize traits of agronomic interest. We used 23 ISSR molecular markers in an attempt to maximize genetic variability among and within populations based on selection of S(1) progenies. To this end, 138 full-sib families were evaluated in a randomized block design in two environments (the municipalities of Campos dos Goytacazes and Itaocara, in the State of Rio de Janeiro, Brazil), with replications within sets. Direct selection for grain yield was used for the selection of the families. To assess genetic diversity among and within populations, we examined plants produced from part of the S(1s) seeds from the parents that originated the 42 full-sib families that were selected from the agronomic traits. Direct selection for grain yield provided good gains for the traits evaluated, with estimated improvement of -0.87 days for days to flowering, 0.35 plants, 1.79 ears per plot, 0.58 g per 100-grain weight, 308.21 g ear weight per plot, and 261.83 kg/ha grain yield. Application of molecular markers at the stage of superior progeny selection led to increased genetic distance among populations, which is a very important factor for utilization of heterosis and providing greater longevity to the reciprocal recurrent selection program.

Experimental modification of reciprocal recurrent selection in oil palm breeding in Cameroon

Reciprocal recurrent selection (RRS) exploits the genetic complementarity of dura populations of palms with a small number of large bunches and tenera/pisifera group of palms with large number of small bunches. An extra phase was introduced to RRS just after the second cycle of selection where outstanding dura derived from (DA3D × DA5D) combinations of the second cycle were self-pollinated for seed production. Best palms based on the phenotype were selected and crossed with pisifera of second cycle offspring of LM2T. [(DA3D × DA5D) self-pollinated × LM2T self-pollinated] progenies were field tested at La Dibamba (Cameroun) from 1987 to 1997. They were precocious with regard to the three-first years’ bunch yields (13.16–15.77 t/ha). Homogeneity for all bunch yield components and homogeneity for vertical growth were illustrated by low values of the variation coefficient (5.75–7.75%). The oil yield was 107% of the control against 115% from [(DA3D × DA5D) × LM2T self-pollinated] progenies of the second cycle of RRS, mostly due to poor mesocarp to fruit and poor oil to mesocarp ratios which led to a low oil extraction rate. The extra selection phase led mainly to homogenisation of progenies but also reduced the fruit quality. However, three progenies whose average oil yield represented 115% of the control (4.87 t/ha) in addition to their precocity can be released to oil palm growers. The extension of RRS did not fully meet expectations and poses the problem of its reliability.

Heterozygous genotypes are efficient testers for assessing between-population combining ability in the reciprocal recurrent selection of Coffea canephora

Coffea canephora Pierre breeding in Cote d’Ivoire is based on indirect reciprocal recurrent selection (RRSi) using the Congolese and Guinean populations. In practice, the genotypes of each population (78 Congolese genotypes and 100 Guinean genotypes) are tested with several testers from the reciprocal population: two Guinean and three Congolese testers. These testers are heterozygous as C. canephora is a strictly outcrossing species. After a first cycle of RRSi, we judged the efficiency of these testers for yield, susceptibility to coffee leaf rust (SCLR) and hundred bean weight (HBW). All the testers discriminated the tested genotypes highly significantly (P < 0.01), even though differences were found in the degrees of discrimination. For yield and SCLR, no interaction between tested genotypes and testers was observed and correlations between test values obtained from different testers were significant or highly significant. Furthermore, test values of tested genotypes could be used to predict the yield and SCLR of between-population (BP) hybrids. Prediction was always more accurate with the best tester than with the mean of several testers. As opposed to yield and SCLR, HBW showed significant interactions between tested genotypes and testers and HBW of hybrids could not be predicted from the test value of the genotypes. We conclude that only one reciprocal tester can be used in the next cycles of RRSi applied to C. canephora. This will allow either a reduced cost of selection or increased selection intensity.

Responses to reciprocal recurrent selection and changes in genetic variability in IG-1 and IG-2 maize populations

This paper reports the effects of three cycles of reciprocal recurrent selection (RRS) on the means, genetic variances, and on the genetic correlations for several traits in the IG-1 and IG-2 maize (Zea mays L.) populations. Interpopulation full-sib progenies from cycle zero (C0) and from cycle 3 (C3) of RRS were evaluated in two locations. RRS was highly effective to improve the traits according the objectives of the program: grain yield and prolificacy increased significantly, while plant height, ear height, and ear placement decreased significantly. Genetic variances for all traits decreased significantly from C0 to C3, but the genetic correlations did not change consistently across the cycles of selection. The expected responses to the fourth cycle of RRS and the probability of selecting double-crosses from C3 that outperform those from C0 showed that the decreases in the genetic variances were not great enough to limit the continued improvement of the populations as well as the use of the improved populations as sources of inbred lines to develop commercial hybrids. However, if the magnitudes of the genetic variances continue to decrease, new sources of improved germplasm should be incorporated into both populations to allow the continued improvement of the interpopulation by RRS.

Response to Selection and Genetic Drift in Three Populations Derived from the Golden Glow Maize Population

Reciprocal recurrent selection (RRS) in maize (Zea mays L.) is used to develop populations with superior combining ability, and it is usually assumed that these populations must be genetically distinct for RRS to be effective. Starting from two randomly derived subpopulations, GG(A) and GG(B), of the open‐pollinated maize population ‘Golden Glow’ (GGC0), we conducted six cycles of full‐sib RRS for grain yield and moisture. Our objectives were to (i) document selection response; (ii) evaluate inter and intrapopulation genetic diversity; and (iii) review selection response relative to gene action, heterosis, inbreeding, and genetic drift. We performed a generation means analysis (GMA) using GG(A), GG(B), and a third population of Golden Glow developed by 21 cycles of mass selection for prolificacy, GG(MP). Field performance was evaluated at four environments in Wisconsin. We analyzed allele frequency changes using simple sequence repeats (SSRs) and amplified fragment length polymorphisms (AFLPs). Selection response for grain yield of GG(A) × GG(B) population crosses was 5.3 g plant−1 cycle−1 Grain moisture and root lodging decreased by −0.5% cycle−1 and −5.2% cycle−1, while prolificacy increased by 0.03 ears cycle−1 After six cycles of RRS, GG(A) and GG(B) diverged genetically from each other, as well as from GG(MP)C21 and Golden Glow. Gene diversity within GG(A) and GG(B) decreased. However, total gene diversity over both GG(A) and GG(B) did not change over cycles of RRS. Genetic drift did not appear to seriously impede selection response. Most of the selection response, regardless of trait, selection method, or subpopulation, was attributed to additive genetic effects.