scholarly journals Inbreeding depression and heterosis of litter size in mice

1960 ◽  
Vol 1 (2) ◽  
pp. 262-274 ◽  
Author(s):  
J. C. Bowman ◽  
D. S. Falconer
Keyword(s):  
Population Size ◽  
Litter Size ◽  
Inbreeding Depression ◽  
Inbreeding Coefficient ◽  
Farm Animals ◽  
The Mean ◽  
Selection For ◽  
Rate Of Decline ◽  
The One ◽  
Crossing Point

1. A random bred population of mice was subjected to inbreeding and the changes of litter size, measured as the number of live young in first litters, were followed.2. The mean litter size declined at a rate of 0·56 young per 10% increase of the inbreeding coefficient.3. Selection for large litters within the lines during the inbreeding did not effectively reduce the rate of decline.4. Out of twenty lines at the beginning of the inbreeding seventeen were lost by the time the inbreeding coefficient reached 76%. Two more were lost later and one survived indefinitely. The three lines that survived longest started at a level below the mean and did not decline in litter size. The one that survived indefinitely reached 99% inbreeding without dropping below the non-inbred control.5. The three lines surviving at 81% inbreeding were crossed and the litters produced by the crossbred progeny were larger than the non-inbred control by about two young per litter. This gain from heterosis is attributable to selection among the lines on their performance as inbreds. A second and third cycle of inbreeding and crossing yielded no further progress, and the level of the first cross was never regained. This is attributable to the ineffectiveness of the selection applied and to the previous restrictions of the population size.6. The behaviour of the lines in the inbreeding and crossing point to simple dominance rather than over-dominance at the loci causing variation of litter size.7. This experiment suggests that, as a means of improvement of farm animals, cyclical inbreeding and crossing does not look very hopeful.

scholarly journals IDENTITY COEFFICIENTS IN FINITE POPULATIONS. I. EVOLUTION OF IDENTITY COEFFICIENTS IN A RANDOM MATING DIPLOID DIOECIOUS POPULATION

Genetics ◽  
1977 ◽  
Vol 86 (3) ◽  
pp. 697-713
Author(s):  
C Chevalet ◽  
M Gillois ◽  
R F Nassar
Keyword(s):  
Genetic Variability ◽  
Population Size ◽  
Effective Population Size ◽  
Random Mating ◽  
Matrix Multiplication ◽  
Inbred Lines ◽  
Inbreeding Coefficient ◽  
Effective Population ◽  
The Mean ◽  
Over Time

ABSTRACT Properties of identity relation between genes are discussed, and a derivation of recurrent equations of identity coefficients in a random mating, diploid dioecious population is presented. Computations are run by repeated matrix multiplication. Results show that for effective population size (Ne) larger than 16 and no mutation, a given identity coefficient at any time t can be expressed approximately as a function of (1—f), (1—f)3 and (1—f)6, where f is the mean inbreeding coefficient at time t. Tables are presented, for small Ne values and extreme sex ratios, showing the pattern of change in the identity coefficients over time. The pattern of evolution of identity coefficients is also presented and discussed with respect to N eu, where u is the mutation rate. Applications of these results to the evolution of genetic variability within and between inbred lines are discussed.

scholarly journals Heterosis in the second and third generation affects litter size in a crossbreed mink (Neovison vison) population

2014 ◽  
Vol 66 (3) ◽  
pp. 1097-1103 ◽  
Author(s):  
Janne Thirstrup ◽  
Cino Pertoldi ◽  
Peter Larsen ◽  
Vivi Nielsen
Keyword(s):  
Litter Size ◽  
Maternal Effects ◽  
Inbreeding Depression ◽  
Neovison Vison ◽  
Parental Line ◽  
Third Generation ◽  
Black Line ◽  
Environmental Variations ◽  
The Mean ◽  
One Year

Litter sizes in a cross between Brown and Black mink color types were observed through six generations. Litter size was significantly affected by yearly environmental variations. After adjusting for year effects, we found significant increases in litter size in the second and third generations (F2 and F3) after crossing. Thereafter, in the following generations, litter size dropped to a level comparable to the mean litter size of the midparent. Increased litter size in F2 compared to F1 indicated that maternal effects influenced litter size more than non-maternal effects. The heterosis was mainly caused by an increase in litter size compared to the Black parental line. This indicates that the Black line was affected by inbreeding depression prior to crossing. We also found that two-year old F1 females had significantly more offspring compared to one-year old F1 females.

scholarly journals The effects of inbreeding on the components of litter size in mice

1967 ◽  
Vol 10 (1) ◽  
pp. 73-80 ◽  
Author(s):  
J. C. McCarthy
Keyword(s):  
Litter Size ◽  
Inbreeding Depression ◽  
First Generation ◽  
Inbreeding Coefficient ◽  
Ovulation Rate ◽  
Corpora Lutea ◽  
Base Population ◽  
Pregnant Females ◽  
Sib Mating ◽  
Size At Birth

Twenty-four lines were bred from a base population of outbred Q mice by continued full-sib mating. Inbreeding depression in litter size at birth was observed. This decline in litter size was analysed in terms of ovulation rate, the incidence of preimplantation mortality and the incidence of postimplantation mortality. Pregnant females were dissected at 17½ days' gestation and the numbers of corpora lutea, or eggs, and of live and dead embryos were counted. Matings were arranged so that separate estimates of the effects of inbreeding in the mother and in the litter on the components of litter size could be obtained.In the first generation of inbreeding when the inbreeding coefficient of the litter was raised from 0 to 25% decline in litter size was attributable to an increased incidence of preimplantation mortality.In the second and fourth generations decline in litter size was attributable to (1) a reduction in the number of eggs ovulated by the inbred mothers, (2) an increased incidence of preimplantation mortality which resulted from inbreeding in the mother. No evidence of significant effects on mortality of inbreeding in the litter was obtained in the later generation of inbreeding.These findings are discussed in the context of previous work on the effects of inbreeding and crossing on litter size and its components in mice and pigs.

scholarly journals Influence of parentage upon growth in Ostrea edulis: evidence for inbreeding depression

2000 ◽  
Vol 76 (2) ◽  
pp. 159-168 ◽  
Author(s):  
YAMAMA NACIRI-GRAVEN ◽  
SOPHIE LAUNEY ◽  
NICOLAS LEBAYON ◽  
ANDRE GERARD ◽  
JEAN-PIERRE BAUD
Keyword(s):  
Inbreeding Depression ◽  
Genetic Relatedness ◽  
Protozoan Parasite ◽  
Control Population ◽  
Ostrea Edulis ◽  
The Family ◽  
Bonamia Ostreae ◽  
Sib Families ◽  
The Mean ◽  
Selection For

Genetic variability for growth was analysed in three populations of Ostrea edulis, selected for resistance to the protozoan parasite Bonamia ostreae. This study was undertaken first to determine the potential for selection for growth in populations that have never been selected for this character, and second to estimate heterosis versus inbreeding depression. Growth was monitored in culture for 10 months. The selected populations (namely S85-G3, S89I-G2 and S89W-G2), their crossbred population and a control population were composed of full-sib families whose parents were already genotyped using five microsatellite markers. This genotyping allowed the estimation of genetic relatedness among pairs of parents. The parents' relatedness was then correlated with the growth performance of their offspring within each of the three populations, and inbreeding depression was estimated. The population effect for growth was highly significant, with the crossbred population having the highest growth rate, followed by S89I-G2 and S89W-G2, S85-G3 and the control population. The within-populations family effect was also highly significant, indicating, as well as the high value for heritability at the family level (between 0·57 and 0·92), that a potential for a further selection for growth still exists within the three populations. Estimates of inbreeding depression (relative to the mean, for complete inbreeding) were high (1 for S891-G2, 0·44 for S89W-G2 and between 0·02 and 0·43 for S85-G3), which correlates with the apparent heterosis for growth observed in the crossbred population. These results are discussed in the context of the future management of the selected populations.

A note on the relationship between litter size at birth and litter weight at weaning in domesticated and feral mice

1981 ◽  
Vol 33 (2) ◽  
pp. 219-222
Author(s):  
W. R. Congleton
Keyword(s):  
Assortative Mating ◽  
Litter Size ◽  
Indirect Selection ◽  
Litter Weight ◽  
The Mean ◽  
Selection For ◽  
The Relationship ◽  
Size At Birth

ABSTRACTThe relationship between litter size at birth and litter weight at weaning is curvilinear, with an intermediate litter size resulting in the heaviest litter weight at weaning. Relative to feral mice, the mean and variation for litter size at birth was larger for domesticated mice which had been selected for fertility and crossbred. Consequently, some of the litters from the crossbred domesticated mice were larger than the litter size at birth which optimized litter weight at weaning, primarily due to increased pre-weaning mortality. If litter weight at weaning is to be optimized by indirect selection for litter size at birth, the variation around an intermediate optimum litter size at birth could be most effectively reduced by negative assortative mating.

A note on the improvement of a trait by selecting on its components

1967 ◽  
Vol 9 (1) ◽  
pp. 127-130 ◽  
Author(s):  
Charles Smith
Keyword(s):  
Litter Size ◽  
Coefficient Of Variation ◽  
Farm Animals ◽  
Direct Selection ◽  
Component Trait ◽  
Component Traits ◽  
Selection For ◽  
Fleece Weight

Many traits in farm animals, such as litter size or fleece weight, are the product or ratio of two or more component items. This note seeks to determine the circumstances in which selection directed at the component items is more effective in improvement than selection for the composite trait itself.A change of one per cent in a product trait can be achieved by a change of one per cent in any of its components. The response expected on selection for a product trait or a component is proportional to h2C per cent, where h2 is the heritability and C is the coefficient of variation. Thus selection for a component trait (A) may possibly be more efficient than direct selection for the product trait (X) when is greater than . However, the correlated changes in other component traits would also have to be taken into account.

Inbreeding effects on some reproductive traits in Markhoz goats

2018 ◽  
Vol 58 (12) ◽  
pp. 2178 ◽  
Author(s):  
P. Mahmoudi ◽  
A. Rashidi ◽  
M. Razmkabir
Keyword(s):  
Litter Size ◽  
Inbreeding Depression ◽  
Reproductive Traits ◽  
Information Criterion ◽  
Inbreeding Coefficient ◽  
Regression Coefficients ◽  
Litter Weight ◽  
Inbreeding Coefficients ◽  
Poisson Models ◽  
The Individual

The objective of this study was to estimate the inbreeding coefficient and its effects on reproductive traits in Markhoz goats. The pedigree file included 5351 kids produced by 234 bucks and 1470 does. Average inbreeding coefficient for the whole population was 2.68%, and the minimum and maximum inbreeding coefficients were 0.05% and 31.25%, respectively. Average coefficient of inbreeding for inbred population was 5.17% and the number of inbred animals in the population was 2777. For investigating effects of inbreeding coefficient on reproductive traits, 3443 records were available for litter size at birth (LSB), litter size at weaning (LSW), total litter weight at birth (TLWB) and mean of litter weight at birth (MLWB). Furthermore, available records for total litter weight at weaning (TLWW) and mean of litter weight at weaning (MLWW) were 2918. Inbreeding depression was estimated as the linear regression of performance on the individual inbreeding coefficient of kids and dams using the most appropriate animal model based on Akaike’s information criterion. Furthermore, inbreeding depressions for LSB and LSW were estimated using threshold and Poisson models. Regression coefficients of LSB, LSW, TLWB, TLWW, MLWB and MLWW on inbreeding coefficient of kids were –0.035, –0.019, –0.077 kg, –0.782 kg, –0.009 kg and –0.332 kg, respectively. Furthermore, regression coefficients of LSB, LSW, TLWB, TLWW, MLWB and MLWW on inbreeding coefficient of dams were 0.064, –0.013, 0.241 kg, 0.638 kg, 0.028 kg and –1.783 kg, respectively. The obtained results from this study showed that inbreeding depression is controlled by an appropriate mating system policy.

scholarly journals Models of long-term artificial selection in finite population with recurrent mutation

1986 ◽  
Vol 48 (2) ◽  
pp. 125-131 ◽  
Author(s):  
William G. Hill ◽  
Jonathan Rasbash
Keyword(s):  
Population Size ◽  
First Generation ◽  
Finite Population ◽  
Effective Population ◽  
Term Selection ◽  
Cumulative Response ◽  
Mean And Variance ◽  
The Mean ◽  
Selection For

SummaryThe effects of mutation on mean and variance of response to selection for quantitative traits are investigated. The mutants are assumed to be unlinked, to be additive, and to have their effects symmetrically distributed about zero, with absolute values of effects having a gamma distribution. It is shown that the ratio of expected cumulative response to generation t from mutants, , and expected response over one generation from one generation of mutants, , is a function of t/N, where t is generations and N is effective population size. Similarly, , is a function of t/N, where is the increment in genetic variance from one generation of mutants. The mean and standard deviation of response from mutations relative to that from initial variation in the population, in the first generation, are functions of . Evaluation of these formulae for a range of parameters quantifies the important role that population size can play in response to long-term selection.

scholarly journals The effects on litter size of crossing lines of mice inbred without selection

1960 ◽  
Vol 1 (2) ◽  
pp. 239-252 ◽  
Author(s):  
R. C. Roberts
Keyword(s):  
Natural Selection ◽  
Litter Size ◽  
Combining Ability ◽  
Variance Components ◽  
Inbred Lines ◽  
Inbreeding Coefficient ◽  
Basic Information ◽  
Outbred Population ◽  
Combining Abilities ◽  
The Mean

1. The experiment was designed to provide basic information relevant to the utilization of heterosis in animal improvement. The character studied was the size of the first litter in mice.2. Thirty inbred lines were crossed at random when the inbreeding coefficient reached 0·50 (three full-sib matings). The lines had been inbred without selection except for natural selection operating with lines.3. The mean litter size of the crossbred mice did not exceed that of the outbred population from which the inbred lines had been derived. This indicates that the increased litter size normally associated with crossbred mice must be ascribed to some form of selection other than within-line natural selection.4. Estimates were obtained of the variance components associated with general and special combining abilities. As anticipated, these estimates were very small, especially those relating to special combining ability. Before selection between crosses becomes possible, high levels of inbreeding must be achieved.

Measurement of fleece wettability in sheep and its relationship to susceptibility to fleece rot and blowfly strike

1982 ◽  
Vol 33 (1) ◽  
pp. 141 ◽  
Author(s):  
L Pascoe
Keyword(s):  
Genetic Variance ◽  
Additive Genetic Variance ◽  
Genetic Correlations ◽  
Economic Importance ◽  
Correlated Response ◽  
Response To Selection ◽  
Significant Incidence ◽  
The Mean ◽  
Selection For ◽  
The One

Fleece wettability in sheep is a character believed to be related to susceptibility to fleece rot and blowfly strike. The present study was undertaken to investigate that hypothesis and to assess wettability as a possible character for a selection program. Wool samples were taken from two flocks which had been subject to selection for wool quality and resistance to fleece rot and a third flock which was unselected. The wettabilities of about 800 samples were determined. The results were found to be repeatable and the technique was capable of distinguishing between sheep. Some problems of measurement are discussed. In the one flock with a significant incidence of fleece rot, susceptibility to fleece rot was found to be associated with higher wettabilities. The mean wettability and the variance were found to be significantly higher in the unselected flock than in the two selected flocks. The heritability of wettability was estimated in the two selected flocks and was found to be low. It is argued that there is likely to be more additive genetic variance in the unselected flock and that the observed difference in wettability was due to a correlated response to selection for resistance to fleece rot. It is considered that further work on the heritability of wettability and its genetic correlations with other characters of economic importance could be fruitful.

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