10.4 Positional cloning Flashcards
What is the purpose of positional cloning?
To identify disease-causing genes by genetic linkage to polymorphic loci
What is the strategy of positional cloning?
It is the same as linkage analysis in using two phenotypes, except one gene is tracked by phenotype, the other by DNA genotype.
Use microarrays to simultaneously analyse millions of two-point crosses, each one a test for linkage between a disease locus and a DNA marker.
What are the steps involved in positional cloning?
- The region of interest is narrowed by finding closely linked DNA markers. Candidate genes are located in the region of interest.
- Sequence and expression of candidate genes are determined in normal and diseased individuals.
Give an example of positional cloning
Neurofibromatosis-
1. Autosomal, dominantly inherited
2. Causes proliferation of nerve tissue
3. Positional cloning example determines whether or not a SNP is linked to the neurofibromatosis gene. Generation III is the result of testcross.
What are the 3 limitations of positional cloning?
- Configuration of alleles is not always known
- Not all matings are informative
- Difficult to obtain sufficient pedigree data in humans
Which disease gene is located by large family pedigree?
Huntington disease gene
Mapping of Huntington disease:
Detection of linkage between the DNA marker G8 and the HD locus.
What is the Lod score ?
It is a statistical tool for studying linkage. It is used to determine if data is sufficient to conclude with confidence that a disease gene and a marker are linked.
What is the formula for Lod score?
log= [P(observed results if loci are linked at a given RF)/P(observed results if loci are unlinked]
What are the two types of heterogeneity that genetic diseases can display?
allelic or locs
What is allelic heterogeneity?
Disease caused by different mutations in the same gene. (individuals with certain alleles may respond to drug treatment, while others do not)
What is a compound heterozygote ?
an individual with different mutant alleles of the same gene.
What is locus heterogeneity?
disease caused by a mutation in one of two or more different genes.
