18 Gene mapping Flashcards
Why gene map?
ID disorders, new Dx/Tx
What is linkage analysis?
Close genes linked = less likely separated, distance in centimorgan
How can numbers of crossovers determine what may occur to an allele?
Single crossovers may alternate all alleles before the crossover point but a double crossover may bring back the original allele if it is not involved in the region of crossover
How is centimorgan equate to recombination chance?
1 cM = 1% chance of recombination(alleles touching). 50 cM = 50% max chance of recombo (alleles at opposite ends)
When does chromosomes reorganize?
Meiosis
What is a linkage phase?
Description of where alleles are located in a pedigree
What is a LOD score?
Statistical result to calculate likelihood of two alleles are linked
What LOD score indicates linkage? What score for no linkage?
3 or higher is significant for linkage. -2 or below is no linkage
What are commonly used for markers in linkage phase?
Microsatellites are useful as they are polymorphic and located everywhere on genome. Can be followed if close enough to allele and unimproved even when likely
What is uninformative mating?
Markers that cannot determine linkage due to not enough polymorphisms
How does linkage relate with time?
Linked alleles/markers will initially stay together but eventually become unlinked
What is linkage disequilibrium?
Mutation with linked allele being inherited together
How is age determined for linked mutations?
Linked mutations estimated by time to equilibrium (close link = longer time)
What is genetic association?
Allele’s effect = increased risk of disorder
How does genetic association compare with linkage?
Association = specific allele found = increased risk but can be anywhere on chromosome
What is an example of genetic association?
HLA-B27 = 90x incr risk of ankylosing spondylitis
What are genome wide association studies?
Technique used to screen many markers at once (usually SNPs)
How can chromosome anomalies ID genes?
Common regions may indicate genes with specific breakpoints
What are the two types of DNA libraries?
Genomic = all DNA from organism. cDNA all genes from a given tissue
What are candidate genes?
DNA sequences possibly responsible for trait
How are candidate genes IDed?
Positionally from sequenced region. Functionally from sequence with predicted function on a given chromosome. Candidate genes must fit both.
How are candidate genes “elected”?
Normal+mutant sequences compared>expression in tissues>compare>express specific gene to find product and function
