A Critical Analysis of IQ Studies of Adopted Children

The Flynn effect is the rise in mean IQ scores during the 20th century, amounting to about 0.33 IQ points per year. Many theoretical explanations have been proposed, though none are universally accepted. W. Dickens and J. R. Flynn's (2001) new approach explains the large IQ changes by means of recursive models of IQ growth. A salient feature of their models is that IQ phenotypes and their supportive environments are correlated; in addition, environmental effects can rebound on phenotypic IQ to increase or lower IQ. In this critique, the authors examine an empirical challenge to their models, which typically imply large changes in IQ variance. However, the historical rise in IQ mean level has not been accompanied by substantial variance changes, a finding inconsistent with the properties of the proposed model.

Twenty-eight hybrids produced from diallel crossing excluding reciprocals among eight parents were studied along with the parents for combining ability for yield and 12 yield components. The study revealed the importance of both additive and non-additive gene effects in governing yield and most of the yield components with preponderance of non-additive gene action for most of the yield components. The analysis of variance for combining ability indicated that mean square due to general combining ability (GCA) was significant for all the characters except for number of tillers/m2, panicle length (cm), number of spikelets /panicle, number of fertile spikelets / panicle, 1000 – grain weight(g) and grain yield(tha-1) which was non significant. Mean square due to specific combining ability (SCA) were significant for all the characters except for spikelets/panicle, fertile spikelets/panicle, 1000-grain weight(g) and grain yield(tha-1) which were non significant. This suggests the importance of both additive and non-additive gene effects in the materials under study. The parent WAB 450-I-B-163-41 was found to be a good general combiner. The hybrids WAB 56-144-FX x WAB 56-100, WAB 450-1-B-163-41 x IRAT 317,WAB 450 -1-B163-41 x IR 47-701-6-3-1, WAB 450-1-B-163-41 x IRAT 239,WAB 35-1-FX x WAB 56 -100, WAB 35 -1-FX x WAB 56-100, IRAT 239 x WAB 56 -100 and IRAT 317 x IRAT 239 have shown significant favorable (SCA) effect for yield and different yield components. Since non- additive/dominance components were higher than the additive components for all the characters in both F1 and F2 generations, bi parental mating and/or reciprocal recurrent selection could be used for genetic improvement of these characters.Keywords: Diallel analysis, combining ability, additive and non additive gene effects, GCA effect, SCA effect.

Groundnut chlorotic rosette disease (GCRD) transmitted by the aphid, Aphis craccivora, is an important virus disease of groundnut in Africa. Breeding for host resistance remains the best strategy to minimize losses due to this disease. Nine cultivated groundnut genotypes with differential reaction to GCRD were crossed in an incomplete diallel mating design to determine the combining ability of GCRD resistance. The parents and 36 F2 populations were inoculated with veruliferous A. craccivora at the seedling stage and evaluated for disease reaction at two locations in Nigeria in 2012. Disease incidence (based on visual symptoms) was recorded three times at fortnightly interval using area under disease progress curve. General combining ability (GCA) and specific combining ability (SCA) effects for GCRD resistance were highly significant (P < 0.01), indicating that both additive and non-additive gene effects governed the inheritance of GCRD resistance. The Baker ratio was low (0.3) for GCRD indicating that non-additive gene effects was more important than additive gene effects in controlling GCRD resistance in these crosses. As a result, progeny performance could not be adequately predicted from GCA effects alone. Therefore, effective selection of superior genotypes would be achieved at advanced generations when maximum homozygosity is attained. Key words: Groundnut chlorotic rosette disease, area under disease progress curve, combining ability, additive and non-additive gene effects.

Within the paradigm of population dynamics a central task is to identify environmental factors affecting population change and to estimate the strength of these effects. We here investigate the impact of observation errors in measurements of population densities on estimates of environmental effects. Adding observation errors may change the autocorrelation of a population time series with potential consequences for estimates of effects of autocorrelated environmental covariates. Using Monte Carlo simulations, we compare the performance of maximum likelihood estimates from three stochastic versions of the Gompertz model (log–linear first order autoregressive model), assuming 1) process error only, 2) observation error only, and 3) both process and observation error (the linear state–space model on log‐scale). We also simulated population dynamics using the Ricker model, and evaluated the corresponding maximum likelihood estimates for process error models. When there is observation error in the data and the considered environmental variable is strongly autocorrelated, its estimated effect is likely to be biased when using process error models. The environmental effect is overestimated when the sign of the autocorrelations of the intrinsic dynamics and the environment are the same and underestimated when the signs differ. With non‐autocorrelated environmental covariates, process error models produce fairly exact point estimates as well as reliable confidence intervals for environmental effects. In all scenarios, observation error models produce unbiased estimates with reasonable precision, but confidence intervals derived from the likelihood profiles are far too optimistic if there is process error present. The safest approach is to use state–space models in presence of observation error. These are factors worthwhile to consider when interpreting earlier empirical results on population time series, and in future studies, we recommend choosing carefully the modelling approach with respect to intrinsic population dynamics and covariate autocorrelation.

Five homozygous lines of castor plant, namely RS1-Om, RN1-Om, RTl-2m, RSl- Owm, and RNl- Omb, were crossed to raise F1, F2, BC1, and BC2 generations. The hybrids were tested for hybrid vigour for two metric traits, viz; number of pods per plant and seed yield per plant. Highly significant hybrid vigour was detected for both traits in all the crosses. The contributions of additive and non-additive gene effects to both traits were also investigated. Additive gene effects were more relevant in the inheritance of number of pods per plant. The effects of the digenic interactions, coupled with the highly significant additive gene effects on number of pods per plant in most of the crosses, tend to suggest that improvement of the character can be enhanced by the use of breeding methods such as the reciprocal recurrent selection that would encourage the concentration of genes involved in the inheritance of the trait. The contributions of dominance gene effects to the total genetic variance were positive and highly significant in both pod and seed yield per plant in all the hybrids. This would tend to favour hybridization and the use of first generation hybrids as an effective means of improving both traits in castor plant. Thus, reciprocal recurrent selection and the use of hybrid programmes are the breeding strategies suggested for the improvement of pod and seed yield in castor plant. Ghana Jnl agric. Sci. Vol.31(1) 1998: 81-86

Basic information on genetics and inheritance of quantitative characters, which is necessary to develop future breeding programme, is not widely studied in pigeonpea. Hence, present study was conducted among 5 generations in four pigeonpea crosses to know significance of additive-dominance model, gene action involved in inheritance of quantitative characters, heritability and genetic advance. “Scaling” and “joint scaling test” was significant for most characters indicating that additive-dominance model alone is not enough to explain the inheritance of a character. Though additive variance was more, dominance variance also played important role for most of the traits. Positive and negative alleles were found to be distributed between parents. Additive gene effect (d) was significant for pods per plant and seeds per pod whereas dominance gene effect (h) was more predominant among pod yield and seed yield. Dominance × Dominance inter-allelic interactions (l) was more important than Additive × Additive type (i) for most of the traits studied which could be exploited by selecting individuals based on their performance in recurrent selection. Complementary gene action was observed among many traits with few exhibiting duplicate gene action. Heritability and genetic advance was high indicating the effectiveness of selection. Since dominance effects is also present along with additive effects selection could be practised in later generations to identify high yielding genotypes.

Combining ability analysis in complete diallel cross of waxy corn (Zea mays var. ceratina) for starch pasting viscosity characteristics

The leafhopper (Empoasca kraemeri Ross and Moore) is a serious pest of common bean (Phaseolus vulgaris L.) in Latin America. Previous studies showed that different leafhopper defense mechanisms were present in bean lines, although all lines suffered considerable damage when leafhopper populations were high. Studies were undertaken to determine the inheritance and combining ability of leafhopper defense mechanisms in beans under field conditions. Bean lines EMP 81 and EMP 82, tolerant to leafhopper feeding damage, and lines EMP 89, EMP 94, and EMP 97, containing antixenosis resistance (a defense mechanism that makes these lines less preferred for leafhopper oviposition) were selected to study. A generation means analysis using EMP 81, EMP 89, and EMP 94, in crosses with a susceptible line, BAT 41, showed that the additive‐dominance genetic model was sufficient to explain the inheritance of tolerance and antixenosis defense mechanisms in these lines. Additive and dominance gene effects were significant for yield of plants under leafhopper attack and feeding damage, although dominance gene effects appeared to be more important in the inheritance of yield. Only additive gene effects were significant for nymphal counts. Similar results were found in the estimation of general and specific combining ability effects in a diallel study of F1 and F2 progeny of crosses among the five resistant bean lines. Certain crosses combining antixenosis and tolerance defense mechanisms resulted in higher F2 yields than would be expected on the bases of the mean performance of their parental lines. The results suggest that transgressive segregation for higher resistance levels may result from crosses among bean lines containing different defense mechanisms.

Dominance may be an important source of non-additive genetic variance for many traits of dairy cattle. However, nearly all prediction models for dairy cattle have included only additive effects because of the limited number of cows with both genotypes and phenotypes. The role of dominance in the Holstein and Jersey breeds was investigated for eight traits: milk, fat, and protein yields; productive life; daughter pregnancy rate; somatic cell score; fat percent and protein percent. Additive and dominance variance components were estimated and then used to estimate additive and dominance effects of single nucleotide polymorphisms (SNPs). The predictive abilities of three models with both additive and dominance effects and a model with additive effects only were assessed using ten-fold cross-validation. One procedure estimated dominance values, and another estimated dominance deviations; calculation of the dominance relationship matrix was different for the two methods. The third approach enlarged the dataset by including cows with genotype probabilities derived using genotyped ancestors. For yield traits, dominance variance accounted for 5 and 7% of total variance for Holsteins and Jerseys, respectively; using dominance deviations resulted in smaller dominance and larger additive variance estimates. For non-yield traits, dominance variances were very small for both breeds. For yield traits, including additive and dominance effects fit the data better than including only additive effects; average correlations between estimated genetic effects and phenotypes showed that prediction accuracy increased when both effects rather than just additive effects were included. No corresponding gains in prediction ability were found for non-yield traits. Including cows with derived genotype probabilities from genotyped ancestors did not improve prediction accuracy. The largest additive effects were located on chromosome 14 near DGAT1 for yield traits for both breeds; those SNPs also showed the largest dominance effects for fat yield (both breeds) as well as for Holstein milk yield.

A triple test cross analysis was carried out to study the genetics of some panicle related traits of agronomic importance in "Basmati" rice. Partitioning of total epistasis into i type and j + l type of epistasis revealed that j + l types of interactions were significant for number of panicle per plant and yield per plant. Additive and dominance gene effects were important for panicle length, number of secondary branches per panicle, number of filled grains per panicle, number of sterile grains per panicle and panicle density. However, additive effects were the only source of variation for number of primaryv branches per plant and fertility percentage. The magnitude of additive variance was higher for all the traits and the degree of dominance was less than unity indicating partial dominance. The non-significant correlation between sums and differences did not show any evidence of directional dominance. Epistatic interactions j + l type can be manipulated to improve number of panicles per plant and yield per plant through recurrent selection. The predominance of additive gene effect suggests the occurrence of selection in late segregating populations however, early selection is proposed for number of primary branches per panicle and fertility percentage to improve rice yield.

The inheritance of resistance to ear rot, caused by Stenocarpella maydis, was investigated using a complete diallel cross of 10 inbred lines, ranging from resistant to susceptible. Parents, F1 crosses and reciprocals were evaluated at each of three localities, representative of different environments within the South African maize production area. Plants were artificially inoculated twice during the vegetative stages of development. Based on the incidence of rotted ears, resistance to S. maydis was found to be controlled by additive gene effects with low dominance and interaction effects. Sufficient GCA and SCA effects existed in the resistant inbred lines to serve as donor parents for the improvement of susceptible germplasm. Inbreds D0620Y and MON1 showed good general combining ability for resistance whereas inbreds B37 and E739 were noted for specific combining ability. Sources of variation that could be employed to breed for improved husk cover and ear declination were identified. However, it was shown that these would not necessarily contribute towards resistance. Genotype × environment effects were pronounced, indicating the necessity to conduct resistance evaluations in a variety of localities.

In 2018 summer season at Gemmeiza Research Station, eleven new yellow inbred lines were crossed with three testers: two inbred lines Gz.658 and Gm.6052) and one single cross SC 162 according to line x tester design. In 2019 summer season the resulting, 33 crosses and four check hybrids: two single crosses (SC 168 and SC 3084) and two three way crosses (TWC 360 and TWC 368) were evaluated at both of Gemmeiza and Sids experimental Research Stations. Significant and highly significant mean squares due to crosses and the partitions lines, testers and lines x testers were obtained for all studied traits across locations, except testers for grain yield. K2 SCA (non- additive gene effects) were more important than K2 GCA (additive gene effects) for all traits Gm.2, Gm.6, Gm.9 and Gm.35 had desirable values for GCA effects for grain yield. The best cross for SCA effects was Gm. 9 × SC. 162 for grain yield. Five single crosses, (Gm. 2 × Gz 658 (28.956 ard /fed), Gm. 35 × Gz 658 (27.777 ard /fed), Gm. 2 × Gm. 6052 (27.566 ard /fed), Gm. 6 x Gm. 6052 (28.157 ard /fed) and Gm. 35 × Gm. 6052 (28.123 ard /fed) did not significantly out-yielded the highest check SC 168 (27.190 ard/fed), while three- way cross Gm. 9 × SC. 162 (29.74 ard/fed) significantly out-yielded the best check TWC 360 (26.42 ard/fed)

Seven rice varieties (Hassani, Deilmani, Sepidruod, Shahpasand, Saleh, Neda and IRFAON215) and their complete diallel progenies were grown in a randomized complete block design with three replications in the growing seasons of 2006 and 2007 at the Rice Research Institute of Iran (RRII) in Rasht. Genetic components, the mode of inheritance and heterosis of various physiological traits were studied by using seven-parent diallel mating design including reciprocals. Results revealed that both additive and non-additive gene effects were important for inheritance of days to flowering, plant height and panicle exsertion with preponderance of additive gene effects. Inheritance of harvest index was controlled only by additive effects. While, inheritance of grain yield, panicle length and flag leaf area were governed by non-additive gene effects. ‘F’ value, showing an excess of dominant alleles in the parents, was significant only for grain yield. The average degree of dominance (H1/D) 0.5 was within the range of partial dominance for days to flowering, plant height, panicle exsertion and harvest index. At least two major groups of genes controlled the inheritance of plant height, and panicle length and flag leaf area, four major groups the inheritance of harvest index and one group the inheritance the other traits. The highest value of relative heterosis was observed for panicle exsertion and grain yield. Wr-Vr graphic analysis indicated that increase of flag leaf area, plant height, panicle exsertion and panicle length was under the control of dominance alleles, but harvest index was increased by recessive alleles. Due to the importance of non-additive components for grain yield, panicle length and flag leaf area, biparental mating and/or reciprocal recurrent selection could be used for genetic improvement of these characters. Predominance of additive effects for remainder of the traits demonstrated that breeding methods based on selection may be advantageous in improving of these traits in rice using the studied materials.

Camelina biotypes had different responses to freezing stress, which was mainly inherited by additive gene effects and can be reliably used in breeding programs and for a better understanding of freezing tolerance mechanisms in camelina plants. Camelina [Camelina sativa (L.) Crantz] is a frost-tolerant oilseed plant that is cultivated as an autumn crop in semi-arid regions. However, camelina establishment in these areas is limited by low temperatures in winter that results in decreased seed yield. In the present study, genetic basis of freezing tolerance (FT) in spring and winter biotypes of camelina was analyzed at seedling stage using a diallel cross experiment. The parents consisted of two winter doubled haploid (DH) lines with high (DH34 and DH31), two spring lines with medium (DH19 and DH26), and two spring lines with low FT (DH08 and DH91). For this purpose, the parents along with F1 entries were subjected to freezing stress and survival percentage, electrolyte leakage, and lethal temperature for 50% mortality (LT50) of the lines were measured. Results showed that although both additive and non-additive effects of the genes determine the FT, further analyses indicated that it was mainly controlled by the additive effects. Therefore, selection-based methods may be more efficient for improving FT in camelina genotypes. The results of specific combining ability (SCA) and heterosis analysis among various DH lines suggested that more tolerant cultivars of camelina could be developed by targeted crossings. When a tolerant winter line and a susceptible spring line were crossed, their progenies showed a higher FT compared with the progenies of a cross between two susceptible spring lines indicating FT is controlled by additive effects of the genes in camelina plants. These findings provided new insight into the genetic basis of freezing-related traits in camelina and could be used for more sophisticated breeding programs.

Inheritance of Several Plant Type Characters in Truss Tomato