遗传学课件第7章基因定位

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"Gene mapping" refers to the mapping of genes to specific locations on chromosomes. It is a critical step in the understanding of genetic diseases. There are two types of gene mapping:
Genetic Mapping - using linkage analysis to determine the relative position between two genes on a chromosome.
Physical Mapping - using all available techniques or information to determine the absolute position of a gene on a chromosome.
and B2 are the two awk.baidu.comleles of locus B.
recombination value (P45)
大量实验表明，两个基因之间的重组值 是相对恒定的，不同基因之间的重组值 却不同，这表明生物体的各个基因在染 色体上的位置是相对恒定的。
The recombination frequency depends on the distance between the two loci and the position of crossover (the chiasma). The closer they are, the less likely the recombination will occur, because recombination occurs only when the chiasma is located between the two loci.
Crossing-over
A locus may have different sequences, referred to as alleles. Consider two loci A and B, each having
two alleles (one from mother, another from father). A1 and A2 are the two alleles of locus A ; B1
In 1985, the gene was mapped to chromosome 7q31-q32 by linkage analysis. Four years later, it was cloned by Collins F. and his coworkers. We now know that the disease is caused by the defect of a chloride channel - the protein product of this disease gene.
For example:
Cystic fibrosis (CF,囊肿性纤维化,属遗传性胰腺病) is the most common lethal inherited disease in the U. S. As many as 1 in 2500 Americans of Northern European descent carry a gene with CF.
Linkage analysis
The genetic mapping is based on the linkage between "loci" (locations of genes). If two
loci are usually inherited together, they are said to be "linked". Two loci on different chromosomes are not linked, because they are usually separated by independent assortment.
这是基因定位的最基本方法。(P126-127) 2 三点测交（three-point testcross） 是通过一次杂交和一次测交，同时确定3对 等位基因的排列顺序和它们之间的遗传距离， 是基因定位的常用方法。 (P127-128)
遗传学课件第7章基因定位
内容
• 基本概念和基本方法 • 人类基因定位的基本方法 • 真菌类生物（脉孢霉）的遗传分析 • 体细胞交换与基因定位 • 细菌的基因定位 • 噬菌体的重组作图
Gene No. Chromosome No. Linkage
4131 genes
Human: ~20,500 genes
基因定位（gene mapping）
将基因定位于某一特定的染色体上，以及测定基因在染色体上 线性排列的顺序与距离
图距
（map distance） （1 mu = 1 cM )
Detecting linkage through testcross
基因定位的基本方法:
1 两点测交（two-point testcross） 是指每次只测定两个基因间的遗传距离，
Early studies of genetic linkage: Morgan’s experiments with Drosophila
• X-linkage genes, w (white eye) and m (miniature wing)
• Morgan crossed a white miniature (w m / w m) female fly with wild-type male (w+ m+ / Y) （P39）
The ultimate goal of gene mapping is to clone genes, especially disease genes. Once a gene is cloned, we can determine its DNA sequence and study its protein product.