Strategic marker selection to detect quantitative trait loci in chicken

Abstract

Selective genotyping for a certain trait in individuals with extreme phenotypes contributes sufficient information to determine linkage between molecular markers and quantitative trait loci (QTL). In this experiment an F 2 population, developed by crossing males from a broiler line with females from a layer line, was employed to detect QTL on chromosomes 3 and 5. Twenty-eight performance and carcass traits were measured in F 2 offspring, and phenotypic correlations between traits were calculated. Body weight at 42 days (BW42) presented the greatest positive correlations with most other traits, with correlation between body weights at 35 and 41 days, weight gain between birth and 35, 41 and 42 days, as well as weights of carcass and some body parts superior to 0.8. One hundred-and-seventy F 2 offspring, representing the top (4.5%) and the bottom (4.5%) of a normal distribution curve of BW42, were selected with equal proportions of males and females, and within dam family. Samples were genotyped for 19 informative markers on chromosome 3, and 11 markers on chromosome 5. Marker allelic frequencies of phenotypic groups with high and low BW42 were compared with a chi-square test. Four regions on chromosome 3 and three regions on chromosome 5 had markers that were suggestively associated with BW42 (P < 0.10), confirming and expanding previous studies. Key words: QTL, broiler, selective genotyping, body weight SELEÇÃO ESTRATÉGICA DE MARCADORES PARA DETECÇÃO DE LOCOS PARA CARACTERÍSTICAS QUANTITATIVAS EM AVESRESUMO: A genotipagem seletiva de indivíduos com fenótipos extremos para uma determinada característica contribui com informação suficiente para determinar a ligação entre marcadores moleculares e locos para características quantitativas (QTL). Neste estudo uma população F 2 , formada a partir do cruzamento de uma linha parental de aves para corte com uma linha de postura foi empregada para obtenção de medidas fenotípicas e genotipagem por marcadores microssatélites, posicionados nos cromossomos 3 e 5. Foram medidas 28 características de desempenho e carcaça e determinada a correlação fenotípica entre elas. A característica peso vivo aos 42 dias (BW42) apresentou maior correlação positiva com a maioria das características, com correlação entre pesos vivos aos 35, 41 dias, ganhos de peso do nascimento aos 35, 41 e 42 dias, e pesos de carcaça e partes superiores a 0,8. Cento e setenta aves F 2 , representando 4,5% das aves mais leves e 4,5% das mais pesadas para BW42 foram selecionadas dentro de famílias, na mesma proporção de machos e fêmeas e genotipadas para 19 marcadores informativos no cromossomo 3 e 11 no cromossomo 5. As freqüências alélicas dos marcadores nos grupos fenotípicos de alto e baixo BW42 foram comparadas empregando teste de qui-quadrado. Foram identificadas quatro regiões no cromossomo 3 e três regiões no cromossomo 5 sugestivamente ligadas a QTL para BW42 (P < 0,10), confirmando e expandindo estudos anteriores de mapeamento de QTL em aves.

Endogamy and genetic variability in selective mating using distribution of extremes

“…The distribution of the extremes gets equivalence in the delay of endogamy by allowing larger family sizes in comparison with the other two strategies, however, considering families of smaller sizes (Table 3), while the genetic variability presented better magnitudes for larger families which used the selective strategy in analogy with those of smaller sizes that did not adopt selective mating (Table 4). These results corroborated the reduction in the number of individuals required in the analysis of quantitative loci for a given capacity of QTL detection, as reported by Darvasi & Soller (1992), Jannink (2005) and Ruy et al (2005).…”

“…This way, according to Bovenhuis and Spelman (2000), Ruy et al (2005) and Rosa (2007), it is acceptable that the application of the distribution of extremes in selective mating brings better results for the characteristic on which individuals were selected. Individuals of one part of the progeny contribute more to the information of marker linking and QTL than others.…”

“…Selective mating, following the methodology of selective genotyping using the distribution of extremes, is a strategy to increase the capacity of detection of quantitative trait loci (Jin et al, 2004;Ruy et al, 2005;Rosa, 2007). In selective mating, individuals present in the upper and lower extremes of a normal distribution of genetic or phenotypic parameter assessed in the experimental population were used (Bovenhuis & Spelman, 2000).…”

Genotypic characterization of microsatellite markers in broiler and layer selected chicken lines and their reciprocal F1s

“…These populations have been used for QTL mapping for performance and carcass traits Ruy et al, 2005;Ambo et al, 2008).…”

Genetic linkage maps of chicken chromosomes 6, 7, 8, 11 and 13 from a Brazilian resource population

“…Each male was mated to three unrelated females selected randomly to generate 21 F 1 families, with approximately 100 chicks per family, in 17 incubations, totalizing 2,063 F 2 animals. The construction of the genetic linkage map of chromosomes 6, 7, 8, 11 and 13, used the five informative families indicated in a previous selective genotyping study of chromosomes 1 to 5 in this population (Baron, 2004;Nones et al, 2005;Ruy et al, 2005). TT was selected for various generations for growth related traits, such as body weight, whereas CC was selected for egg production traits .…”