scholarly journals Accumulation of mutations affecting body weight in inbred mouse lines

1995 ◽  
Vol 65 (2) ◽  
pp. 145-149 ◽  
Author(s):  
Armando Caballero ◽  
Peter D. Keightley ◽  
William G. Hill
Keyword(s):  
Body Weight ◽  
Maximum Likelihood ◽  
Genetic Variance ◽  
Inbred Mouse ◽  
Additive Genetic Variance ◽  
Selection Response ◽  
Spontaneous Mutations ◽  
Line Selection ◽  
Divergence Estimates ◽  
Mouse Lines

SummaryThe variation from spontaneous mutations for 6-week body weight in the mouse was estimated by selection from a cross of two inbred sublines, C57BL/6 and C57BL/10, separated about 50 years previously from the same inbred line. Selection was practised high and low for 12 generations from theF2, followed by one generation of relaxation. The lines diverged by approximately 1·7 g or 0·7 sd. The additive genetic variance was estimated in theF2by restricted maximum likelihood and from the selection response, and from this variance the mutational heritabilityhM2was estimated using the number of generations since divergence. Estimates ofhM2range from 0·08 to 0·10% depending on the method of analysis. These estimates are similar to those found for other species, but lower than other estimates for the mouse. It is concluded that substantial natural and, perhaps, artificial selection operated during the maintenance of the sublines.

scholarly journals Estimation of variance components for bodyweight of grasscutters using expectation maximization algorithm of restricted maximum likelihood

2020 ◽  
Vol 44 (5) ◽  
pp. 5-8
Author(s):  
I. Udeh
Keyword(s):  
Body Weight ◽  
Maximum Likelihood ◽  
Expectation Maximization ◽  
Variance Components ◽  
Genetic Variance ◽  
Phenotypic Variability ◽  
Additive Genetic Variance ◽  
Expectation Maximization Algorithm ◽  
Estimation Of Variance ◽  
Selection Of

The objective of this study was to estimate the variance components and heritability of bodyweight of grasscutters at 4, 6 and 8 months of age using EM algorithm of REML procedures. The data used for the study were obtained from the bodyweight records of 20 grasscutters from four families at 4, 6 and 8 months of age. The heritability of bodyweight of grasscutters at 4, 6 and 8 months of age were 0.14, 0.10 and 0.12 respectively. This implies that about 10 – 14 % of the phenotypic variability of body weight in this grasscutter population was accounted by additive genetic variance while environmental and gene combination variance made a larger contribution. The implication is that selection of grasscutters in this population should not be based on the information on the animals alone but also information fromits relatives.

scholarly journals Standing genetic variation as a major contributor to adaptation in the Virginia chicken lines selection experiment

2015 ◽  
Author(s):  
Zheya Sheng ◽  
Mats E Pettersson ◽  
Christa F Honaker ◽  
Paul B Siegel ◽  
Örjan Carlborg
Keyword(s):  
Body Weight ◽  
Genetic Variation ◽  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Selection Response ◽  
Selective Sweeps ◽  
Base Population ◽  
A Genome ◽  
Wide Scale ◽  
Genomic Regions

Artificial selection has, for decades, provided a powerful approach to study the genetics of adaptation. Using selective-sweep mapping, it is possible to identify genomic regions in populations where the allele-frequencies have diverged during selection. To avoid misleading signatures of selection, it is necessary to show that a sweep has an effect on the selected trait before it can be considered adaptive. Here, we confirm candidate selective-sweeps on a genome-wide scale in one of the longest, on-going bi-directional selection experiments in vertebrates, the Virginia high and low body-weight selected chicken lines. The candidate selective-sweeps represent standing genetic variants originating from the common base-population. Using a deep-intercross between the selected lines, 16 of 99 evaluated regions were confirmed to contain adaptive selective-sweeps based on their association with the selected trait, 56-day body-weight. Although individual additive effects were small, the fixation for alternative alleles in the high and low body-weight lines across these loci contributed at least 40% of the divergence between them and about half of the additive genetic variance present within and between the lines after 40 generations of selection. The genetic variance contributed by the sweeps corresponds to about 85% of the additive genetic variance of the base-population, illustrating that these loci were major contributors to the realised selection-response. Thus, the gradual, continued, long- term selection response in the Virginia lines was likely due to a considerable standing genetic variation in a highly polygenic genetic architecture in the base-population with contributions from a steady release of selectable genetic variation from new mutations and epistasis throughout the course of selection.

scholarly journals Selection strategies of segregant soybean populations for resistance to Asian rust

2009 ◽  
Vol 44 (11) ◽  
pp. 1452-1459 ◽  
Author(s):  
Aliny Simony Ribeiro ◽  
José Francisco Ferraz de Toledo ◽  
Magno Antonio Patto Ramalho
Keyword(s):  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Infected Leaf ◽  
Good Resistance ◽  
Narrow Sense Heritability ◽  
Growing Seasons ◽  
Selection Strategies ◽  
Line Selection ◽  
Soybean Resistance ◽  
Selection Of

The objective of this work was to identify the best selection strategies for the more promising parental combinations to obtain lines with good resistance to soybean Asian rust (Phakopsora pachyrhizi). Two experiments were carried out in the field during the 2006/2007 and 2007/2008 growing seasons, to determine the percentage of infected leaf area of individual plants of five parents and their segregant F2 and F3 populations. The data obtained indicates that additive genetic variance predominates in the control of soybean resistance to Asian rust, and that the year and time of assessment do not significantly influence the estimates of the genetic parameters obtained. The narrow-sense heritability (h²r) ranged from 23.12 to 55.83%, and indicates the possibility of successful selection of resistant individuals in the early generations of the breeding program. All the procedures used to select the most promising populations to generate superior inbred lines for resistance to P. pachyrhizi presented similar results and identified the BR01-18437 x BRS 232 population as the best for inbred line selection.

Genetic and environmental causes of variation in birth weight of Black Bengal goats

1970 ◽  
Vol 74 (3) ◽  
pp. 409-414 ◽  
Author(s):  
S. K. Moulick ◽  
O. Syrstad
Keyword(s):  
Body Weight ◽  
Birth Weight ◽  
Litter Size ◽  
Partial Correlation ◽  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Maternal Environment ◽  
Breeding Station ◽  
Environmental Causes ◽  
Partial Correlation Coefficient

SUMMARYAn investigation on the different environmental and genetic causes of variation in the birth weight of Black Bengal goats was conducted at the Central Livestock Research-cum-Breeding Station, Haringhata, India. The data consisted of 1375 birth weight records of kids from 284 does and 20 bucks during the period from 1955 to 1961. The goats were maintained under standard farm management throughout the period.Year had significant effect on birth weight, while the effect of season was insignificant. The interaction was, however, significant. Male kids were significantly heavier at birth than the females. Age of dam and litter size also caused significant variation in birth weight of kids.From paternal half-sib analysis the heritability of birth weight was estimated to be 0·01. Full sib and maternal half sib analyses estimated the maternal environment common to litter mates to account for 60 % of the variance, out of which 25 % were due to permanent differences between dams. The remaining 39 % were attributed to individual environment, including most of the non-additive genetic variance. The heritability of maternal environment was estimated to be 0·2.The partial correlation coefficient between birth weight of kids and post-kidding body weight of their dam, independent of litter size and age of dam, was 0·175. Thus, body size of dam, as indicated by post kidding body weight, did not reveal much information about maternal environment.

scholarly journals The limits to artificial selection for body weight in the mouse: IV. Sources of new genetic variance—irradiation and outcrossing

1967 ◽  
Vol 9 (1) ◽  
pp. 87-98 ◽  
Author(s):  
R. C. Roberts
Keyword(s):  
Body Weight ◽  
Artificial Selection ◽  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Negative Results ◽  
Selection For ◽  
The Cross

1. Two methods are examined of introducing new genetic variance into a line of mice selected for high 6-week weight which, at its limit, displayed no additive genetic variance.2. The first method—irradiation—gave largely negative results. Any further gain under selection that was achieved could not be clearly distinguished from a possible environmental trend.3. The second method—outcrossing to an unselected strain and then selecting from the cross—resulted in a clear gain over the original limit, but nine generations were required even to recover the original limit.4. Various methods of transcending selection limits are evaluated in terms of their application to livestock improvement.

scholarly journals A complex multi-locus, multi-allelic genetic architecture underlying the long-term selection-response in the Virginia body weight line of chickens

2017 ◽  
Author(s):  
Yanjun Zan ◽  
Zheya Sheng ◽  
Lars Rönnegård ◽  
Christa F. Honaker ◽  
Paul B. Siegel ◽  
...  
Keyword(s):  
Body Weight ◽  
Additive Genetic Variance ◽  
Natural Populations ◽  
Selection Response ◽  
Multiple Alleles ◽  
Term Selection ◽  
Selection Responses ◽  
Genome Wide ◽  
Genetic Mechanisms

AbstractThe ability of a population to adapt to changes in their living conditions, whether in nature or captivity, often depends on polymorphisms in multiple genes across the genome. In-depth studies of such polygenic adaptations are difficult in natural populations, but can be approached using the resources provided by artificial selection experiments. Here, we dissect the genetic mechanisms involved in long-term selection responses of the Virginia chicken lines, populations that after 40 generations of divergent selection for 56-day body weight display a nine-fold difference in the selected trait. In the F15 generation of an intercross between the divergent lines, 20 loci explained more than 60% of the additive genetic variance for the selected trait. We focused particularly on seven major QTL and found that only two fine-mapped to single, bi-allelic loci; the other five contained linked loci, multiple alleles or were epistatic. This detailed dissection of the polygenic adaptations in the Virginia lines provides a deeper understanding of genome-wide mechanisms involved in the long-term selection responses. The results illustrate that long-term selection responses, even from populations with a limited genetic diversity, can be polygenic and influenced by a range of genetic mechanisms.

scholarly journals Genetic variation in varying environments

1981 ◽  
Vol 37 (1) ◽  
pp. 79-93 ◽  
Author(s):  
Trudy F. C. Mackay
Keyword(s):  
Body Weight ◽  
Genetic Variation ◽  
Spatial Heterogeneity ◽  
Temporal Variation ◽  
Genetic Variance ◽  
Environmental Variability ◽  
Additive Genetic Variance ◽  
Environmental Variation ◽  
Heterogeneous Environments ◽  
Varying Environments

SUMMARYIn order to assess the relationship between genetic and environmental variability, a large natural population of Drosophila melanogaster was replicated as eight subpopulations, which were subjected to four different patterns of environmental variation. The environmental variable imposed was presence of 15% ethanol in the culture medium. Experimental treatments of the populations were intended to simulate constant environmental conditions, spatial heterogeneity in the environment, and two patterns of temporal environmental variation with different periodicity (long- and short-term temporal variation). Additive genetic and phenotypic variation in sternopleural and abdominal chaeta number, and body weight, were estimated in two successive years, and measurements were taken of the genotype–environment correlation of body weight and sternopleural bristle score with medium type.Additive genetic variance of sternopleural chaeta number and of body weight was significantly greater in the three populations experiencing environmental heterogeneity than in the control population, but additive genetic variance of abdominal bristle score was not clearly affected by exposing populations to varying environments. Temporal environmental variation was equally, if not more, efficient in promoting the maintenance of genetic variation than spatial heterogeneity, but the cycle length of the temporal variation was of no consequence. Specific genotype–environment interactions were not present, therefore adaptation to heterogeneous environments is by selection of heterozygosity per se, rather than by differential survival of genotypes in the alternate niches.

scholarly journals The limits to artificial selection for body weight in the mouse II. The Genetic Nature of the Limits

1966 ◽  
Vol 8 (3) ◽  
pp. 361-375 ◽  
Author(s):  
R. C. Roberts
Keyword(s):  
Body Weight ◽  
Natural Selection ◽  
Artificial Selection ◽  
Sharp Increase ◽  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Base Population ◽  
Relaxed Selection ◽  
Genetic Nature ◽  
Selection For

1. The effects of long-continued selection for body weight in two lines of mice, one large and one small, are described.2. The large line showed a sharp increase in weight after remaining at an apparent limit for twenty generations. A rare combinational event is suggested as the most likely explanation.3. Reversed and relaxed selection from the large line at the limit failed to yield any response. This indicates that effectively, the additive genetic variance in this line had been exhausted.4. In contrast, the small line at the limit regressed slightly towards the base population when selection was relaxed. Reversed selection yielded a ready response until a new limit was apparently reached. Loci affecting body weight in this line had therefore not been fixed by selection.5. Natural selection, operating on viability between conception and the time when the selection was made, appears to explain best the lack of fixation in the small line.6. Attention is drawn to the necessity of more experimental work to elucidate the genetic nature of the limits to artificial selection.

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