专题一：QTL和其定位方法(esr).ppt

专题一：QTL及其定位方法 QTL的概念 QTL检测方法 用于QTL定位的群体 统计方法 图距函数 QTL检测所需标记数预估 QTL的概念 1、A QTL is a segment of chromosome affecting the trait, not necessarily a single locus --D. S. Falconer et al, 1995 2、A quantitative trait loci(QTL) is defined as a single gene or a cluster of closely linked genes that have a large effect on a quantitative trait. --P. Sorensen, 2000 QTL的概念 3、QTL, quantitative trait locus, is a place (region) that affects trait in the genome. It could span several genes, one or more of which affects the trait, but it has become common to take QTL as equal to major gene. —— B. Kinghorn, 2000 理解：一个QTL指在基因组中占据一定染色体区域，控制同一性状的一组微效多基因的集合（基因簇）或单个基因。但目前的研究中大部分将QTL理解为单个基因（或主效基因）。一个数量性状可能受多个QTL影响；一个QTL也可能影响多个数量性状。 QTL的概念 QTL的特点（与传统的孟德尔因子比较） 结构更松散，一个QTL内各微效基因间可能有比孟德尔因子内高得多的重组率，因此一个QTL并不象一个孟德尔位点那样独立分离和有明显的性状效应。 QTL的概念 QTL概念提出的意义（D.S. Falconer--1995） 1、It could improve the efficacy of selective breeding, especially for traits with low heritability or that can only be measured in one sex. 2、Transgenic technology might be applied to quantitative traits. ??????? QTL的概念 3、In medicine, the identification of alleles causing predisposition to common multifactorial diseases could lead to improved methods of prevention. 4、Quantitative genetic theory will be made more realistic when the numbers and properties of the genes are known, and the more realistic theories will improve our understanding of evolution (and/or the development of the quantitative traits). QTL检测方法Candidate gene approach(Hayes,2007) The candidate gene approach assumes that a gene involved in the physiology of the trait could harbour a mutation causing variation in that trait. The gene, or parts of the gene, are sequenced in a number of different animals, and any variations in the DNA sequences, that are found, are tested for association with variation in the phenotypic trait. Candidate gene approach There are two problems with the candidate gene approach: Firstly, there are usually a large nu