My dissertation focuses on the design and incentives of survey techniques. As many institutions use surveys to allocate funding or determine policy, ensuring surveys provide accurate information is essential. Though incentives certainly play a role in whether survey participants report information truthfully, economists have largely overlooked the issue while statisticians tend to focus on estimators without directly modeling incentive constraints. One of the chapters models and analyzes the incentives of a commonly used survey technique, randomized response, while the other two chapters of my dissertation design two response techniques which improve upon others found in the literature by obtaining more precise estimates and/or incentivizing participants better. In Chapter One "A Game Theoretic Analysis of the Randomized Response Technique," I explicitly model the decision of participants to truthfully respond in the randomized response survey as a game. Randomized response techniques are used to determine the proportion of a population that belongs to a stigmatized group and introduce noise so the surveyor cannot perfectly infer whether a participant belongs to a stigmatized group, regardless of how a participant responds. The interviewer wants to reduce noise as much as possible while maintaining enough noise to ensure participants respond truthfully. Unlike prior literature, I find that the incentives of a participant depend on the number of participants; therefore, the amount of noise required under randomized response decreases when the number of participants increases as adding respondents relaxes truth-telling constraints. However, adding respondents only relaxes incentive constraints to a limit, so some noise remains even when there are a large number of participants. I improve upon the original randomized response technique in two ways in Chapter 2: "Eliciting Private Information using Correlation: A Modification of Randomized Response." In standard randomized response techniques, participants receive questions independently by using a randomization device such as a die. With my technique, participants receive perfectly correlated questions which reduces the variance of the surveyor's estimator while still protecting the privacy of the subjects. Unlike with the randomized response technique, adding correlation allows the surveyor to use a dominant strategy mechanism though it provides limited information. In addition to correlation, my technique provides the surveyor with private information on the distribution of questions asked. Because of the private information, participants become more uncertain of which question is more associated with the stigmatizing characteristic giving them a stronger incentive to respond truthfully. My final chapter, Chapter 3 "A Response Technique with Dominant Strategies in Forced Responses," improves upon a randomized response technique commonly used in practice. In the forced response technique, a fraction of survey participants are directly asked whether they belong to the stigmatizing group while the remaining participants either simply state "yes" or "no" according to a privately observed command. Unlike the original randomized response technique, the surveyor must worry whether participants obey the command in addition to answering truthfully. Psychologically, participants may feel more inclined to disobey than to lie. Therefore, I design a technique where obeying the command is a dominant strategy by providing the surveyor with private information. The paper then discusses a more general response technique with private information and suggests restrictions on the mechanisms to ensure the surveyor does not have an incentive to try to "trick" respondents into believing they have more privacy protection than they actually do. The chapter concludes with a discussion on privacy measures.

Measures of data quality are important for the evaluation and improvement of survey design and procedures. A detailed investigation of the sources, magnitude and impact of errors is necessary to identify how survey design and procedures may be improved and how resources allocated more efficiently among various aspects of the survey operation. A major part of this thesis is devoted to the overview of statistical theory and methods for measuring the contribution of response variability to the overall error of a survey. A very common practice in surveys is to select groups (clusters) of elements together instead of independent selection of elements. In practice cluster samples tend to produce higher sampling variance for statistics than element samples of the same size. Their frequent use stems from the desirable cost features that they have. Most data collection and sample designs involve some overlapping between interviewer workload and the sampling units (clusters). For those cases, a proportion of the measurement variance, which is due to interviewers, is reflected to some degree in the sampling variance calculations. The prime purpose in this thesis is to determine a variance formula that decomposes the total variance into sampling and measurement variance components for two commonly used data collection and sample designs. Once such a decomposition is obtained, determining an optimum allocation in existence of measurement errors would be possible.

No description available.

Tesis por compendio / The thesis is composed for four articles, where is studied either as relationships between body condition and energetic mobilization in rabbits and as the effect of selection for litter size variability in body condition and energetic mobilization, such as welfare biomarkers, and in litter size and its components after seven generation of selection. The first article examines the relationships between measures of body condition and energetic mobilization on primiparous rabbit at mating, delivery and 10 d after delivery, using principal component analysis. Body condition was measured as body weight and perirenal fat thickness. Energetic mobilization was measured as non-esterified fatty acid concentration in blood, before (NEFAb) and after lipolysis stimulation by isoproterenol (NEFAr). All body weights and perirenal fat thickness were located on the first principal component, exhibiting high correlations between them both at the same or different times (from 0.51 to 0.83). All NEFA measurements were located on the second component, showing low correlations with body condition measurements. Both NEFAs showed high positive correlations when measured at the same time (0.65 at mating, 0.72 at delivery and 0.69 at 10 d after delivery), but low correlations when measured at different times (from 0.09 to 0.20). The second article analyses the correlated response in body condition and fat reserves mobilization. The perirenal fat thickness and the increase in NEFAs from basal until adrenergic stimulation by isoproterenol were measured at second mating, at delivery and at 10 d after delivery. Perirenal fat thickness was similar in both lines at mating. However, the high line showed lower fat thickness than the low line at delivery (-0.16 mm, P=0.86), and this difference remained at 10 d after delivery (-0.17 mm, P=0.86). Moreover, this line exhibited 30% more concentration in NEFAs at delivery than the low one (P=0.96). The third and fourth articles study the correlated responses to selection in litter size and its components. A laparoscopy was performed 12 d of the second gestation, in order to estimate ovulation rate and number of implanted embryos. The litter size was recorded at the second parity. In the last gestation, the embryonic development was analysed at 28, 48 and 72 hours of gestation. The ovulation rate was similar in both lines. The line selected to reduce variability in litter size showed a higher number of implanted embryos (1.23, P=1.00) than the high line. Also, this line showed a more advanced development of the embryos from 48 hours of gestation, exhibiting a lower percentage of early morulae both at 48 hours (53.32% vs 79.90%, P=0.93) and at 72 hours (3.88% Vs. 21.04%, P=0.93). More advanced embryo development is related to higher embryo survival (0.85 vs 0.78, P=1.00). A higher uterine overcrowding of embryos in the low line did not penalise fetal survival, and as a result, this line continued showing a greater number of kits born at birth (0.98, P=0.96). In conclusion, body weight and perirenal fat thickness are good predictors of body reserves and both measurements could be used to estimate energy changes in the mid-long term, while NEFA measurements should be used in the short term. A decrease in litter size variability has a favourable effect on body condition, fat reserve mobilization, embryonic development and survival, and litter size. / La tesis se compone de cuatro artículos, donde se estudia tanto la relación entre la condición corporal y la movilización de energía en la coneja como el efecto de la selección divergente por variabilidad del tamaño de camada en la condición corporal y movilización de reservas energéticas, como biomarcadores del bienestar del animal, y en el tamaño de camada y sus componentes después de siete generaciones de selección. El primer artículo examina las relaciones entre las medidas de la condición corporal y la movilización de energía en conejas primíparas a la monta, al parto y a los 10 días tras el parto, a través de un análisis de componentes principales. La condición corporal se midió como el peso corporal y el espesor de grasa perirenal. La movilización de energía se midió como la concentración de ácidos grasos no esterificados en sangre, antes (NEFAb) y después de la estimulación lipolítica con isoproterenol (NEFAr). Todos los pesos y espesores de grasa perirenal se situaron sobre la primera componente principal, exhibiendo altas correlaciones entre ellos independientemente del estado fisiológico donde se midieron (de 0.51 a 0.83). Todas las medidas de NEFAs se localizaron sobre la segunda componente principal, mostrando una baja correlación con las medidas de la condición corporal. Los NEFAb y NEFAr mostraron elevadas correlaciones entre ellos cuando se midieron en el mismo momento (0.65 a la monta, 0.72 al parto y 0.69 a los 10 días tras el parto), pero bajas correlaciones cuando se midieron en diferentes momentos (de 0.09 a 0.20). El segundo artículo analiza la respuesta correlacionada sobre la condición corporal y la movilización de reservas grasas. El espesor de la grasa perirenal y el incremento de los niveles basales de NEFAs después de su estimulación adrenérgica con isoproterenol fueron medidos a la segunda monta, al parto y a los 10 días tras el parto. El espesor de la grasa perirenal fue similar en ambas líneas a la monta. Sin embargo la línea de alta mostró un menor espesor de grasa que la línea de baja al parto (-0.16 mm, P=0.86), y esta diferencia se mantuvo a los 10 días después del parto (-0.17 mm, P=0.86). Por otro lado, esta línea exhibió un 30% menos de NEFAs al parto que la línea de baja (P=0.96). El tercer y cuarto artículo estudian la respuesta correlacionada sobre el tamaño de camada y sus componentes. Se realizó una laparoscopía a los 12 días de la segunda gestación para estimar la tasa de ovulación y el número de embriones implantados. Se contabilizó el tamaño de camada al segundo parto. En la última gestación se analizó el desarrollo embrionario a 28, 48 y 72 horas de gestación. La tasa de ovulación fue similar en ambas líneas. La línea seleccionada para reducir la variabilidad en tamaño de camada mostró un mayor número de embriones implantados (1.23, P=1.00) que la línea de alta. También, esta línea mostró un desarrollo de los embriones más avanzado a partir de las 48 horas de gestación, exhibiendo un menor porcentaje de mórulas tempranas tanto a 48 horas (53.32% vs 79.90%, P=0.93) como a 72 horas (3.88% vs 21.04%, P=0.93). Un desarrollo más avanzado del embrión está relacionado con una mayor supervivencia de éste (0.85 vs 0.78, P=1.00). Por otro lado, un mayor atestamiento de embriones en el útero de la línea de baja variabilidad no penalizó la supervivencia fetal, y como resultado, esta línea continuó mostrando un mayor número gazapos al parto (0.98, P=0.96). En conclusión, el peso y el espesor de grasa perirenal son buenos predictores de las reservas corporales, ambas medidas podrían usarse para estimar los cambios energéticos a medio plazo, mientras que las medidas de NEFAs se deberían usar a corto plazo. La disminución de la variabilidad del tamaño de camada tiene un efecto favorable sobre la condición corporal, la movilización de reservas grasas, el desarrollo y supervivencia embrionaria y el tam / La tesi es compon de quatre articles, on s'estudia tant la relació entre la condició corporal i la mobilització d'energia en la conilla com l'efecte de la selecció divergent per variabilitat de la grandària de ventrada en la condició corporal i mobilització de reserves energètiques, com biomarcadores del benestar de l'animal, i en la grandària de ventrada i els seus components després de set generacions de selecció. El primer article examina les relacions entre les mesures de la condició corporal i la mobilització d'energia en conilles primípares a la muntada, al part i als 10 dies després del part, a través d'una anàlisi de components principals. La condició corporal es va mesurar com el pes corporal i la grossària de greix perirenal. La mobilització d'energia es va mesurar com la concentració d'àcids grassos no esterificats en sang, abans (NEFAb) i després de l'estimulació lipolítica amb isoproterenol (NEFAr) . Tots els pesos i grossàries de greix perirenal es van situar sobre la primera component principal, exhibint altes correlacions entre ells independentment de l'estat fisiològic on es van mesurar (de 0.51 a 0.83) . Totes les mesures de NEFAs es van localitzar sobre la segona component principal, mostrant una baixa correlació amb les mesures de la condició corporal. Els NEFAb i NEFAr van mostrar elevades correlacions entre ells quan es van mesurar en el mateix moment (0.65 a la muntada, 0.72 al part i 0.69 als 10 dies després del part) , però baixes correlacions quan es van mesurar en diferents moments (de 0.09 a 0.20). El segon article analitza la resposta correlacionada sobre la condició corporal i la mobilització de reserves greixos. La grossària del greix perirenal i l'increment dels nivells basals de NEFAs després de la seua estimulació adrenérgica amb isoproterenol van ser mesurats a la segona muntada, al part i als 10 dies després del part. La grossària del greix perirenal va ser semblant en ambdós línies a la muntada. No obstant això la línia d'alta va mostrar una menor grossària de greix que la línia de baixa al part (-0.16 mm, P=0.86) , i esta diferència es va mantindre als 10 dies després del part (-0.17 mm, P=0.86) . D'altra banda, esta línia va exhibir un 30% menys de NEFAs al part que la línia de baixa (P=0.96). El tercer i quart article estudien la resposta correlacionada sobre la grandària de ventrada i els seus components. Es va realitzar una laparoscopía als 12 dies de la segona gestació per a estimar la taxa d'ovulació i el nombre d'embrions implantats. Es va comptabilitzar la grandària de ventrada al segon part. En l'última gestació es va analitzar el desenrotllament embrionari a 28, 48 i 72 hores de gestació. La taxa d'ovulació va ser semblant en ambdós línies. La línia seleccionada per a reduir la variabilitat en grandària de ventrada va mostrar un nombre més gran d'embrions implantats (1.23, P=1.00) que la línia d'alta. També, esta línia va mostrar un desenrotllament dels embrions més avançat a partir de les 48 hores de gestació, exhibint un menor percentatge de mórulas primerenques tant a 48 hores (53.32% vs 79.90%, P=0.93) com a 72 hores (3.88% vs 21.04%, P=0.93). Un desenrotllament més avançat de l'embrió està relacionat amb una major supervivència d'este (0.85 vs 0.78, P=1.00). D'altra banda, un major atapeïment d'embrions en l'úter de la línia de baixa variabilitat no va penalitzar la supervivència fetal, i com resultat, esta línia va continuar mostrant un nombre més gran errors al part (0.98, P=0.96). En conclusió, el pes i la grossària de greix perirenal són bons predictors de les reserves corporals, ambdós mesures podrien usar-se per a estimar els canvis energètics a mitjà termini, mentres que les mesures de NEFAs s'haurien d'usar a curt termini. La disminució de la variabilitat de la grandària de ventrada té un efecte favorable sobre la condició corporal, la mobilització de reserves greixos, el dese / Calle Ayma, EW. (2017). CORRELATED RESPONSE TO SELECTION FOR LITTER SIZE RESIDUAL VARIANCE IN RABBITS [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/81021 / Compendio

O elevado valor sócioeconômico da soja é atribuído, em grande parte, à combinação muito favorável de altos teores de proteína e óleo, juntamente com níveis adequados de produtividade de grãos. Porém, existe uma alta correlação negativa entre os teores de proteína e óleo, fato que dificulta o melhoramento simultâneo destes caracteres. Além disso, também existe tendência de correlação negativa e moderada entre o teor de proteína e a produtividade de grãos. Existem evidências de que a seleção para densidade da semente pode promover ganhos indiretos simultâneos no teor de proteína e na produtividade de grãos. Assim, os principais objetivos deste trabalho foram: a) estimar parâmetros genéticos relacionados com a herança da densidade da semente; b) avaliar a eficiência da seleção para densidade da semente no melhoramento do teor de proteína e da produtividade de grãos. Para o estudo de herança foram utilizados quatro cruzamentos diferentes: USP98-06.011.10 x Abura, MSOY 8001 x Abura, USP98-06.027.03 x Biloxi e USP98-06.009.01 x PI 239.235, sendo que os parentais e as plantas F2 foram avaliados durante a safra 2006/07. Já para avaliar as respostas correlacionadas à seleção para densidade da semente foram delineados três experimentos distintos: Experimento Inicial, no qual foram avaliadas 520 progênies F7:6, durante a safra 2005/06; Experimento Densidade, em que foram avaliadas 100 progênies F8:6 selecionadas para densidade da semente; Experimento Alimentos, em que foram avaliadas 100 progênies F8:6 selecionadas para soja tipo alimento. Os dois últimos experimentos foram realizados durante a safra 2006/07, e as progênies avaliadas neles foram selecionadas dentre as 520 progênies F7:6 do Experimento Inicial. Os resultados permitiram chegar as seguintes conclusões: a) existe ampla variabilidade genética para densidade da semente; b) a herdabilidade no sentido amplo para este caráter é baixa quando estimada na geração F2, mas em geração avançada de endogamia atinge valor alto; c) a herança genética é aditiva e, assim, o caráter não manifesta heterose; d) existe correlação moderada e positiva da densidade da semente com a produtividade de grãos e o teor de proteína e, por outro lado, a correlação entre a densidade da semente e o teor de óleo é negativa; e) é possível identificar genótipos tipo alimento com médias altas de produtividade de grãos e teor de proteína; f) a seleção para aumentar a densidade da semente é eficiente no melhoramento simultâneo do teor de proteína e da produtividade de grãos, permitindo a obtenção de genótipos com alta produtividade de proteína; g) a seleção para reduzir a densidade da semente não promove aumentos significativos do teor de óleo. / The high socioeconomic importance of soybean is mainly attributed to its much favorable combination of high protein and oil contents, together with appropriate levels of seed yield. However, there is a high negative correlation between protein and oil contents, fact that difficult the simultaneous breeding of these traits. Besides, also there is tendency of negative and moderate correlation between protein content and seed yield. There are evidences that the selection for seed density can promote indirect responses in protein content and seed yield, simultaneously. The main objectives of this work were: a) to estimate genetic parameters related to inheritance of seed density; b) to evaluate the efficiency of selection for seed density in breeding protein content and seed yield. In the inheritance study, four different crosses were used: USP98-06.011.10 x Abura, M-SOY 8001 x Abura, USP98-06.027.03 x Biloxi e USP98-06.009.01 x PI 239.235. The parents and F2 plants were evaluated during the 2006/07 season. For evaluating the correlated responses to selection for seed density three different experiments were designed: the Initial Experiment, in which were evaluated 520 F7:6 progenies, during the 2005/06 season; the Seed Density Experiment, in that were evaluated 100 F8:6 progenies selected for seed density; and the Food Soybean Experiment, in that were evaluated 100 F8:6 progenies selected for food type soybean. The last two experiments were accomplished during the 2006/07 season, and the progenies were selected among the 520 F7:6 progenies of the Initial Experiment. The results allowed the following conclusions: a) there is genetic variability for seed density; b) the broad sense heritability for seed density is low in F2 and high in advanced generations; c) the genetic inheritance is additive, because this, there is no heterosis for seed density; d) there is moderate and positive correlation of seed density with seed yield and protein content, but the correlation between seed density and oil content is negative; e) is possible to identify food type genotypes with high means of seed yield and protein content; f) the selection to increase seed density is efficient in breeding protein content and seed yield simultaneously, obtaining genotypes with high protein yield; g) the selection to reduce seed density promote no significant increases of oil content.

O elevado valor sócioeconômico da soja é atribuído, em grande parte, à combinação muito favorável de altos teores de proteína e óleo, juntamente com níveis adequados de produtividade de grãos. Porém, existe uma alta correlação negativa entre os teores de proteína e óleo, fato que dificulta o melhoramento simultâneo destes caracteres. Além disso, também existe tendência de correlação negativa e moderada entre o teor de proteína e a produtividade de grãos. Existem evidências de que a seleção para densidade da semente pode promover ganhos indiretos simultâneos no teor de proteína e na produtividade de grãos. Assim, os principais objetivos deste trabalho foram: a) estimar parâmetros genéticos relacionados com a herança da densidade da semente; b) avaliar a eficiência da seleção para densidade da semente no melhoramento do teor de proteína e da produtividade de grãos. Para o estudo de herança foram utilizados quatro cruzamentos diferentes: USP98-06.011.10 x Abura, MSOY 8001 x Abura, USP98-06.027.03 x Biloxi e USP98-06.009.01 x PI 239.235, sendo que os parentais e as plantas F2 foram avaliados durante a safra 2006/07. Já para avaliar as respostas correlacionadas à seleção para densidade da semente foram delineados três experimentos distintos: Experimento Inicial, no qual foram avaliadas 520 progênies F7:6, durante a safra 2005/06; Experimento Densidade, em que foram avaliadas 100 progênies F8:6 selecionadas para densidade da semente; Experimento Alimentos, em que foram avaliadas 100 progênies F8:6 selecionadas para soja tipo alimento. Os dois últimos experimentos foram realizados durante a safra 2006/07, e as progênies avaliadas neles foram selecionadas dentre as 520 progênies F7:6 do Experimento Inicial. Os resultados permitiram chegar as seguintes conclusões: a) existe ampla variabilidade genética para densidade da semente; b) a herdabilidade no sentido amplo para este caráter é baixa quando estimada na geração F2, mas em geração avançada de endogamia atinge valor alto; c) a herança genética é aditiva e, assim, o caráter não manifesta heterose; d) existe correlação moderada e positiva da densidade da semente com a produtividade de grãos e o teor de proteína e, por outro lado, a correlação entre a densidade da semente e o teor de óleo é negativa; e) é possível identificar genótipos tipo alimento com médias altas de produtividade de grãos e teor de proteína; f) a seleção para aumentar a densidade da semente é eficiente no melhoramento simultâneo do teor de proteína e da produtividade de grãos, permitindo a obtenção de genótipos com alta produtividade de proteína; g) a seleção para reduzir a densidade da semente não promove aumentos significativos do teor de óleo. / The high socioeconomic importance of soybean is mainly attributed to its much favorable combination of high protein and oil contents, together with appropriate levels of seed yield. However, there is a high negative correlation between protein and oil contents, fact that difficult the simultaneous breeding of these traits. Besides, also there is tendency of negative and moderate correlation between protein content and seed yield. There are evidences that the selection for seed density can promote indirect responses in protein content and seed yield, simultaneously. The main objectives of this work were: a) to estimate genetic parameters related to inheritance of seed density; b) to evaluate the efficiency of selection for seed density in breeding protein content and seed yield. In the inheritance study, four different crosses were used: USP98-06.011.10 x Abura, M-SOY 8001 x Abura, USP98-06.027.03 x Biloxi e USP98-06.009.01 x PI 239.235. The parents and F2 plants were evaluated during the 2006/07 season. For evaluating the correlated responses to selection for seed density three different experiments were designed: the Initial Experiment, in which were evaluated 520 F7:6 progenies, during the 2005/06 season; the Seed Density Experiment, in that were evaluated 100 F8:6 progenies selected for seed density; and the Food Soybean Experiment, in that were evaluated 100 F8:6 progenies selected for food type soybean. The last two experiments were accomplished during the 2006/07 season, and the progenies were selected among the 520 F7:6 progenies of the Initial Experiment. The results allowed the following conclusions: a) there is genetic variability for seed density; b) the broad sense heritability for seed density is low in F2 and high in advanced generations; c) the genetic inheritance is additive, because this, there is no heterosis for seed density; d) there is moderate and positive correlation of seed density with seed yield and protein content, but the correlation between seed density and oil content is negative; e) is possible to identify food type genotypes with high means of seed yield and protein content; f) the selection to increase seed density is efficient in breeding protein content and seed yield simultaneously, obtaining genotypes with high protein yield; g) the selection to reduce seed density promote no significant increases of oil content.

<p>Domestication has led to genetic changes that affect quantitative traits in farm animals. Both candidate gene analysis using association tests and genome scans based on linkage analysis have been performed to understand the molecular basis underlying quantitative genetic variation in horses, pigs and chickens. To test a possible association of polymorphisms in the <i>PRKAG3</i> gene, previously found to be associated with excess glycogen content in pig skeletal muscle, with quantitative traits in the horse, the major coding part of the equine <i>PRKAG3</i> sequence was identified. Bioinformatic characterization of the equine <i>PRKAG3</i> gene was conducted. A single nucleotide polymorphism (SNP) causing a missense mutation (Pro258Leu) was found. Screening this SNP showed that the Leu258 allele was more frequent in breeds with heavy muscularity. To assess previously reported associations between polymorphisms in the <i>MC4R</i> gene and obesity-related traits further, we conducted linkage analysis between the <i>MC4R</i> locus and fatness-related traits using a Wild BoarxLarge White intercross. No significant association between segregation at the <i>MC4R</i> locus and fatness was detected in this pedigree. A genome scan of quantitative trait loci (QTLs) has been performed in an intercross between chicken lines divergently selected for growth. Divergent parental lines have been established by selecting for high and low 56-day body weight for over 40 generations. The selection has led to approximately a 9-fold difference in 56-day body weight between lines and resulted in correlated responses for a number of traits including appetite, immune response, body composition and metabolic traits. Phenotypic data on growth and other correlated traits were collected from more than 800 F2 individuals. Genome scans using 145 markers on 26 linkage groups have identified QTLs affecting growth and correlated responses to selection for 56-day body weight. No major QTL explaining a large portion of phenotypic variation in growth was revealed in this study. </p>

Domestication has led to genetic changes that affect quantitative traits in farm animals. Both candidate gene analysis using association tests and genome scans based on linkage analysis have been performed to understand the molecular basis underlying quantitative genetic variation in horses, pigs and chickens. To test a possible association of polymorphisms in the PRKAG3 gene, previously found to be associated with excess glycogen content in pig skeletal muscle, with quantitative traits in the horse, the major coding part of the equine PRKAG3 sequence was identified. Bioinformatic characterization of the equine PRKAG3 gene was conducted. A single nucleotide polymorphism (SNP) causing a missense mutation (Pro258Leu) was found. Screening this SNP showed that the Leu258 allele was more frequent in breeds with heavy muscularity. To assess previously reported associations between polymorphisms in the MC4R gene and obesity-related traits further, we conducted linkage analysis between the MC4R locus and fatness-related traits using a Wild BoarxLarge White intercross. No significant association between segregation at the MC4R locus and fatness was detected in this pedigree. A genome scan of quantitative trait loci (QTLs) has been performed in an intercross between chicken lines divergently selected for growth. Divergent parental lines have been established by selecting for high and low 56-day body weight for over 40 generations. The selection has led to approximately a 9-fold difference in 56-day body weight between lines and resulted in correlated responses for a number of traits including appetite, immune response, body composition and metabolic traits. Phenotypic data on growth and other correlated traits were collected from more than 800 F2 individuals. Genome scans using 145 markers on 26 linkage groups have identified QTLs affecting growth and correlated responses to selection for 56-day body weight. No major QTL explaining a large portion of phenotypic variation in growth was revealed in this study.