RESUMO
In this study we show that selection based on progeny testing is able to induce a rapid change in allele frequency, even when a fairly broad and balanced breeding goal is applied. The myostatin 3'-UTR mutation (c.*1232G>A) previously found to affect muscularity in Texel sheep is also present in the Norwegian White Sheep population. By genotyping the rams used for artificial insemination (born in1977-2006), a rapid increase in the c.*1232G>A allele frequency was observed, from 0.31 in 1990 to 0.82 in 2006. The major increase was observed after BLUP-based breeding values and the EUROP classification system for carcass quality was implemented in 1991 and 1996, respectively. The MSTN frameshift mutation c.960delG, recently identified in this population, did not show a similar increase in allele frequency during the same period, in spite that it has a strong desirable effect on meat and fat traits. The results also illustrate that unwanted side effects can rapidly be introduced into a population using an efficient breeding scheme. A system for monitoring changes in phenotypic traits additional to those under selection is therefore recommended to identify possible side effects at an early stage.
Assuntos
Frequência do Gene , Miostatina/genética , Seleção Genética , Ovinos/genética , Animais , Cruzamento/métodos , Feminino , Genótipo , Inseminação Artificial/veterinária , Masculino , FenótipoRESUMO
Mutations in the coding region of the myostatin gene (MSTN) are known to cause an increased muscle mass (IMM) phenotype in several mammals, including mice, dogs, cattle and humans. In sheep, a mutation in the 3'-UTR region introducing a microRNA target site has been reported to cause an IMM-like phenotype because of downregulation of translation. Here we report a novel single base deletion in the coding region of the myostatin gene causing an IMM phenotype in Norwegian White Sheep, characterized by a high carcass conformation class and low fat class (EUROP classification system). The deletion disrupts the reading frame from amino acid (aa) position 320, ending in a premature stop codon in aa position 359. In our material, these MSTN mutations segregated in a pattern showing that they reside in two different haplotypes. The phenotypic effect of the single base deletion is more profound than that of the 3'-UTR mutation.
Assuntos
Composição Corporal/genética , Mutação da Fase de Leitura , Miostatina/genética , Carneiro Doméstico/genética , Animais , Haplótipos , Análise dos Mínimos Quadrados , Fenótipo , Análise de Sequência de DNA , Carneiro Doméstico/anatomia & histologia , Carneiro Doméstico/crescimento & desenvolvimentoRESUMO
Norwegian Landrace gilts were inseminated on the second day of their second oestrus and slaughtered 28 to 34 days after insemination. The number of corpora lutea (ovulation rate) and normal embryos was counted and the embryonic survival rate was calculated for the 306 pregnant gilts. Mean (+/-S.D.) ovulation rate, number of normal embryos and embryonic survival rate were 14.17+/-2.48, 10.55+/-3.30 and 74.8%+/-20.7%, respectively. The significant (P<0.001) curvilinear regression of embryonic survival rate on ovulation rate gives a maximum embryonic survival rate at 13.2 ovulations. Increased ovulation rate gives increased number of normal embryos up to 18.1 ovulations. Ovulation rate should be considered when assessing factors affecting embryonic survival in pigs.
