scholarly journals SELECTION FOR A THRESHOLD CHARACTER IN DROSOPHILA IV. CHROMOSOMAL ANALYSES OF PLATEAUED POPULATIONS

Genetics ◽  
1973 ◽  
Vol 73 (3) ◽  
pp. 497-512
Author(s):  
B D H Latter
Keyword(s):  
Genetic Basis ◽  
Major Gene ◽  
Positive Interactions ◽  
Chromosome Substitution ◽  
Bristle Number ◽  
Component Traits ◽  
The Mean ◽  
Selection For ◽  
Chromosome Iii ◽  
Chromosomal Recombination

ABSTRACT Chromosome substitution and intra-chromosomal recombination techniques have been employed to determine the genetic basis of limits to selection in lines selected for high scutellar bristle number from the Canberra population. Three observations indicate the presence of an upper threshold affecting some component traits, which is not readily discernible at the level of the selected phenotype: (1) The variance of the number of anterior + interstitial + posterior bristles is progressively reduced as the mean approaches a total of eight at these sites. Total bristle number, which includes apicals in addition to the above three components, and which was the trait subject to selection, shows little evidence of this phenomenon; (2) the effect of a given chromosome substitution is also greatly reduced as the mean approaches eight anterior + interstitial + posterior bristles, by comparison with its effect in genotypes of lower mean; (3) chromosome substitutions show some evidence of negative interaction as this level is approached, in contrast to the positive interactions evident at higher means. All chromosomes except IV are involved in progress beyond the proposed upper threshold. However, chromosome III has the most important effect, due primarily to a major gene located at approximately 61 cM, which also markedly increases dorsocentral and postvertical bristle numbers.

scholarly journals Studies on The Scutellar Bristles of Drosophila Melanogaster I. Basic Variability, Some Temperature and Culture Effects, and Responses to Short-Term Selection in the Oregon-Rc Strain

1968 ◽  
Vol 21 (4) ◽  
pp. 721 ◽  
Author(s):  
BL Sheldon
Keyword(s):  
Drosophila Melanogaster ◽  
Major Gene ◽  
Selection Response ◽  
Wild Type ◽  
Short Term ◽  
Term Selection ◽  
Bristle Number ◽  
Selection For ◽  
High Selection ◽  
Culture Effects

The results of short runs of disruptive and high selection for scutellar bristles in wild-type Drosophila are explained in terms of the hypothesis that canalization at four bristles is due to regulation of the major gene in the developmental system (Rendel, Sheldon, and Finlay 1965). Selection response has probably been due to selection for modifier (minor) genes rather than for isoalleles of the major gene or weak regulator alleles. Some environmental effects on the character, short runs of selection for low bristle number or different bristle types, and effects of relaxing selection are also reported.

scholarly journals Genetic Basis of Relationship Between Yield and its Component Traits in Rice Revealed by Genome-Wide Association and Mendelian Randomization Study

2020 ◽  
Author(s):  
Jing Su ◽  
Kai Xu ◽  
Chao Wu ◽  
Zirong Li ◽  
Zhongli Hu ◽  
...  
Keyword(s):  
Genetic Basis ◽  
Mendelian Randomization ◽  
Rice Yield ◽  
Genome Wide Association ◽  
Yield Potential ◽  
Genome Wide ◽  
Component Traits ◽  
Selection For ◽  
Ideotype Breeding ◽  
Effect On Yield

Abstract BackgroundRice yield has a complex genetic architecture, which mainly determined by its three component traits: the number of grains per panicle (GPP), kilo-grain weight (KGW) and tillers per plant (TP). Exploring ideotype breeding based on selection for genetically less complex component traits is an alternative route for further improving rice production. Thus, it is important that studying the genetic basis of relationship between rice yield and component traits and clarifying the effects of each component trait on yield. Main textIn this study, we carried out meta-analyses of genome-wide association study (Meta-GWAS) with two population (575 + 1495 F1) in different environment for yield and its three component traits in rice. Totally, 3589 significant loci for three components traits were detected, while only 3 significant loci for yield were detected. It indicated that rice yield is mainly controlled by minor-effect loci and hardly to be identified. Selecting quantitative trait locus (QTL)/gene affected component traits to further enhance yield is recommended. A Mendelian randomization (MR) design was adopted to further estimate the causal relationship between rice yield and its component traits. Both GPP (Beta=0.086, 95% CI: 0.030~0.141, P=0.003) and TP (Beta=1.865, 95% CI: 1.035~2.694, P<0.0001) has a positive causal relationship with yield, but no significant relationship between KGW and yield (Beta=0.456, 95% CI: -0.119~1.031, P=0.120) was observed. Additionally, TP (Beta=1.865) has a greater effect on yield than GPP (Beta=0.086). Four significant loci for TP and GPP with indirect effect on yield were identified. Pyramiding superior alleles of the four loci revealed improved yield. A combination of direct and indirect effects may better contribute to the yield potential of rice.ConclusionsOur results suggested rice production would improve by ideotype breeding based on selection for GPP and TP. By studying the nature and strength of the relationship between yield and its components, provide genetic insights for further improving rice yield potential.

scholarly journals Selection for a threshold character in Drosophila: III. Genetic control of variability in plateaued populations

1970 ◽  
Vol 15 (3) ◽  
pp. 285-300 ◽  
Author(s):  
B. D. H. Latter
Keyword(s):  
Drosophila Melanogaster ◽  
Genetic Variation ◽  
Developmental Regulation ◽  
Allocation Of Resources ◽  
Genetic Changes ◽  
Domestic Species ◽  
Threshold Character ◽  
Bristle Number ◽  
The Mean ◽  
Selection For

SUMMARYAn analysis of populations of Drosophila melanogaster which had ceased to respond to selection for increased scutellar bristle number has disclosed the existence of an overall negative genetic correlation between replicate lines in the frequency of the two major component bristle types, viz. anteriors and posteriors. Negative phenotypic correlations among component bristle sites have also been detected within populations. A model involving competition among sites for the available resources of a particular limiting substrate is therefore proposed. Genetic changes have been effected in exceptional populations which lead either to an increase in the rate of production of the limiting substrate, or to a lowering of the concentration of the substrate necessary for bristle initiation. The allelic substitutions concerned are recessive, and have been described as decanalizing alleles in view of their effects on both bristle number variability and a measure of developmental regulation at individual anterior sites. Genetic variation has also been demonstrated for the mean allocation of resources to each of the four component bristle types, viz. anteriore interstitials, posteriors and apicals. A brief discussion is given of the implications of the model for breeding practice in domestic species.

scholarly journals STUDIES ON THE SCUTELLAR BRISTLES OF DROSOPHILA MELANOGASTER. II. LONG-TERM SELECTION FOR HIGH BRISTLE NUMBER IN THE OREGON RC STRAIN AND CORRELATED RESPONSES IN ABDOMINAL CHAETAE

Genetics ◽  
1972 ◽  
Vol 71 (4) ◽  
pp. 567-595
Author(s):  
B L Sheldon ◽  
M K Milton
Keyword(s):  
Population Level ◽  
Direct Selection ◽  
Correlated Response ◽  
Selection Line ◽  
Wild Type ◽  
Correlated Responses ◽  
Bristle Number ◽  
Dominance Level ◽  
The Mean ◽  
Selection For

ABSTRACT Results are presented of 135 generations of selection for high scutellar bristle number in two lines M and M3 derived from the same original mating of one female with 5 bristles by one male with 4 bristles, the latter being the wild-type canalised phenotype. Results are also given of two relaxed lines per line and of a reselection line M2 derived from the first relaxed line of line M which had regressed almost to base population level. The effect of introducing the sc1 allele into the M and M3 selected backgrounds was studied at generations 39–44. At the end of selection the effect of an extra dose of sc+ was also studied in males of all selected backgrounds. The correlated responses in abdominal bristles were followed in all lines.—Considering their common origin, the selection lines differed markedly in pattern of scutellar response and in most other aspects observed, namely correlated responses in abdominals and p.c. scutellars, sex differences, and behaviour on relaxation. Selection limits for scutellar bristles in lines M and M2 were equal to or greater than the most extreme reported in the literature.—The probit span of the canalised 4 bristle class decreased in each selection line as the mean scutellar bristle number increased, and increased again in the relaxed lines as the mean bristle number decreased. In the context of an hypothesis that canalisation at 4 bristle is due to regulation of the scute locus, this result is now interpreted as being due mainly to selection for poor regulators of sc+, in contrast to a previous interpretation that only the minor gene background was altered by selection, the canalisation (regulation) genotype not being affected.—Introducing the sc  1 allele into the selected backgrounds M and M3 showed a reduced effect on sc  1 flies compared with sc+ flies, and an interaction of sc  1 and sc+ with selected background. sc  1 flies had about the same number of bristles in both backgrounds though the mean of sc+ flies in line M was about 3? higher than in line M3. Dominance of sc+ to sc  1 was reduced slightly in M3. However, the effect of an extra dose of sc+ at the end of selection was about the same as in unselected in all lines, so the first or dominance level of regulation of the scute locus was not significantly affected by selection, though the second or canalisation level of regulation was.—A large positive correlated response in abdominal bristles occurred in all lines. The response in line M was about twice that in M2 and M3 and was in fact as large as can be obtained from direct selection on abdominals. In line M some genes may have been selected with a proportionately greater effect on abdominals than on scutellars. This is supported by the further observation in line M that the abdominal scores of flies with particular scutellar bristles scores increased as the scutellar mean increased. An attempt was made to apply to these results Rendel's (1962) model of competition between scutellars and abdominals for common bristle-making resources. This could not be done satisfactorily mainly because the assumptions in the model about the similarity of effects in scute and wild-type flies were not met in the present material.

scholarly journals Effects of X-rays on response to selection for a quantitative character of Drosophila melanogaster

1967 ◽  
Vol 9 (2) ◽  
pp. 221-231 ◽  
Author(s):  
L. P. Jones
Keyword(s):  
Quantitative Character ◽  
Phenotypic Variance ◽  
X Rays ◽  
Response To Selection ◽  
High Frequencies ◽  
Bristle Number ◽  
Two Generations ◽  
The Mean ◽  
Selection For ◽  
Chromosome Ii

1. Lines with ten pairs of parents and selected at an intensity of 20% were exposed to 1000 r. of X-rays for 0, 2, 10 or 30 generations.Lines which received some irradiation generally gave greater response than the unirradiated controls. The phenotypic variance in the irradiated lines was much higher than in the controls. There was little difference in behaviour between lines receiving ten generations of irradiation and those irradiated every generation. Lines receiving only two generations of irradiation had lower variances than the other irradiated lines, but in one of three replicates the response was greater than the corresponding continuously irradiated line.3. Lethal frequencies were much higher in irradiated than unirradiated lines. Particular chromosome II and III lethals were at high frequencies in most of the irradiated lines but in only two out of five controls.4. On relaxation, the mean of the irradiated lines generally declined considerably, but in the unirradiated lines there was only a very small regression.5. It appears that most of the extra response and increased variance in the irradiated lines were caused by a few genes with large effect on bristle number.

scholarly journals Response to selection from new mutation and effective size of partially inbred populations. II. Experiments with Drosophila melanogaster

1995 ◽  
Vol 66 (3) ◽  
pp. 227-240 ◽  
Author(s):  
Montserrat Merchante ◽  
Armando Caballero ◽  
Carlos López-Fanjul
Keyword(s):  
Drosophila Melanogaster ◽  
Effective Size ◽  
Deleterious Mutations ◽  
Response To Selection ◽  
New Mutation ◽  
Lethal Mutations ◽  
Bristle Number ◽  
The Mean ◽  
Selection For ◽  
Inbred Populations

SummaryDivergent artificial selection for abdominal bristle number in Drosophila melanogaster has been carried out starting from a genetically homogeneous base population. Lines with two different systems of mating, random (P lines) or between full sibs whenever possible (about 50%), random otherwise (I lines) were compared. Responses after 40 generations of selection were mostly due to one or two mutations of large effect (0·2 to 2 phenotypic standard deviations) per line. Ten mutations affecting the selected trait were individually studied (five lethal and five non-lethal, these being predominantly additive). These mutations satisfactorily explain the response attained, although some minor mutations may also be involved. No evidence of epistasis for bristle number was found. The average final divergence was 57% larger in the P lines, but it was mostly due to lethals or highly deleterious mutations. Thus, after relaxation of selection, the ranking reversed and the mean divergence became significantly larger in the I lines (14%). Analysis of inbreeding showed that the very small amount of variation created by spontaneous mutations (a heritability for the selected trait of about 3%) was responsible for a reduction in the effective size of about 50% in the I lines (relative to the case with random selection), but only about 10% in the P lines. Mutational heritabilities estimated from the response to selection (0·05–0·18%) were within the range usually found for this trait in previous experiments. REML estimates account for correlations between relatives, and were much larger in those lines where the response was due to lethal mutations, as these do not contribute to response after reaching maximum frequency.

Composite trait selection to improve reproduction and ewe productivity: a review

2009 ◽  
Vol 49 (1) ◽  
pp. 9 ◽  
Author(s):  
G. D. Snowder ◽  
N. M. Fogarty
Keyword(s):  
Individual Component ◽  
Genetic Relationships ◽  
Reproductive Efficiency ◽  
Component Trait ◽  
Litter Weight ◽  
Growth Selection ◽  
Component Traits ◽  
Selection For ◽  
Genetic Responses ◽  
Lamb Growth

Reproduction and ewe productivity are complex composite traits that are influenced by several component traits. Genetic improvement by selection for an individual component trait may not always be advantageous because adverse or neutral genetic relationships can exist among the component traits. Selection for an overall composite trait of ewe productivity, defined as litter weight weaned per ewe joined, can result in a balanced biological composite trait with favourable responses in component traits including fertility, number of lambs born, lamb survival, lactation and lamb growth. Selection for litter weight weaned may also overcome adverse genetic relationships among reproductive component traits. This review examines the genetic responses of selecting directly for litter weight weaned, compared with selection responses for one or more of its component traits. It is concluded that selection to improve reproductive efficiency and ewe productivity, under most production and environmental systems, would benefit from selection for a composite trait such as litter weight weaned, rather than for a single component trait.

scholarly journals Genetics of naked grain oats in crosses with Brazilian genotypes

2000 ◽  
Vol 23 (4) ◽  
pp. 851-854 ◽  
Author(s):  
Cândida Braga Cabral ◽  
Sandra Cristina Kothe Milach ◽  
Luiz Carlos Federizzi ◽  
Cristhiane Abegg Bothona ◽  
Ivone Taderka ◽  
...  
Keyword(s):  
Avena Sativa ◽  
Major Gene ◽  
Incomplete Dominance ◽  
Naked Oat ◽  
The Usa ◽  
Selection For

Six crosses between three naked oat (Avena sativa L.) germplasm sources from the USA and Australia and three Brazilian hulled genotypes were studied for the segregation of naked grain and multiflorous spikelet traits in the F2 and F3 generations. One major gene with incomplete dominance and expressivity for both traits was identified in all populations. The occurrence of intermediate types for naked grain varied with the population and did not depend on the germplasm source of naked grain used. The frequency of intermediate types varied among F2 populations indicating that selection for higher expressivity of naked grain could be used to develop Brazilian oat lines with naked grain.

scholarly journals Screening of French Bean (Phaseolus vulgaris L.) Genotypes against Alternaria Leaf Spot Caused by (Alternaria alternata) under Dryland Conditions of Kashmir

2021 ◽  
pp. 25-30
Author(s):  
Sabiya Bashir ◽  
Mohammad Najeeb Mughal ◽  
Zahida Rashid ◽  
Shabeena Majid ◽  
Sabeena Naseer ◽  
...  
Keyword(s):  
Alternaria Alternata ◽  
Leaf Spot ◽  
Disease Incidence ◽  
French Bean ◽  
Phaseolus Vulgaris L ◽  
Dryland Agriculture ◽  
Disease Reaction ◽  
The Mean ◽  
Selection For ◽  
Resistant Genotypes

Sixty-three genotypes of  french bean was screened against leaf spot (Alternaria  alternata) in sick plots at Research Farm of Dryland Agriculture Research Srinagar, Rangreth during  Kharif  2018 and 2019. The highest mean disease incidence ranged from 0.00 to 85.00 per cent  with  the mean disease intensity ranged from 0.00 to 53.26 per cent .One genotype namely  ‘Local Pulwama’ was highly susceptible in their disease reaction. Among the screened germplasm, ‘Highly Resistant’ genotypes was SKU-R-601, SKUA-R-105, SKU-R-927, DARS-25, DARS-66, DARS-R-615,  while as ‘Susceptible’ genotypes was  DARS-8, DARS-12,  DARS-11, SKUAST-R-155, SKU-R-928, DARS-7, DARS-R-4, Bhaderwah (L),  Local  Kupwara black and Raj Jawala. Local Pulwama was found to be a highly susceptible (HS) genotype.  Twenty nine genotypes namely., DARS-16, DARS-9, DARS-54, DARS-39, VL-125, DARS-63, ENTO-504, SKUAST-204,SKU-R-925, DARS-60, DARS-109, DARS-43, DARS-44, SKU-R-23, DARS-4, DARS-74, SKU-R-105, DARS-40, DARS-23, DARS-18, SKU-R-71, WB-341, SKU-R-605, Uri local, Shopian (L), SKU-R-23, DARS-71, SSGB-729, DARS-R-19 showed resistant reaction to disease. The selection for resistance was based on the reaction of varieties on leaves.

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