tailieunhanh - Báo cáo sinh học : "Q&A: Genetic analysis of quantitative traits"

Tuyển tập các báo cáo nghiên cứu về sinh học được đăng trên tạp chí sinh học Journal of Biology đề tài: Q&A: Genetic analysis of quantitative traits. | Journal of Biology BioMed Central Question Answer Q A Genetic analysis of quantitative traits Trudy FC Mackay What are quantitative traits Quantitative or complex traits are traits for which phenotypic variation is continuously distributed in natural populations with population variation often approximating a statistical normal distribution on an appropriate scale. Quantitative traits include aspects of morphology height weight physiology blood pressure behavior aggression as well as molecular phenotypes gene expression levels high- and low-density cholesterol levels . What causes the continuous distribution of phenotypes for quantitative traits The continuous variation for complex traits is due to genetic complexity and environmental sensitivity. Genetic complexity arises from segregating alleles at multiple loci. The effect of each of these alleles on the trait phenotype is often relatively small and their expression is sensitive to the environment. Allelic effects can also depend on genetic background and sex. Because of this complexity many genotypes can give rise to the same phenotype and the same genotype can have different phenotypic effects in different environments. Thus there is no clear relationship between genotype and phenotype. Does this mean you can t see Mendelian ratios for quantitative traits Yes because of the small magnitude of the allelic effects on the phenotype. Mendelian variants have large effects on the phenotype so there is a clear correspondence between genotype at a locus and trait phenotype. For any trait there is a continuum of allelic effects from small to large the large effects segregate as Mendelian variants while the small effects segregate as quantitative genetic variation. For example human height is a classic quantitative trait but achondroplasia dwarfism is caused by a Mendelian autosomal dominant mutation in the fibroblast growth factor receptor 3 gene. Why are quantitative traits important Quantitative genetic variation is