How to Make a Genetic Map Jason Morales Department of Agronomy Purdue University
Review What is the difference between a genetic map and a physical map? A physical map is the sequence of nucleotides in the genome. A genetic map is the position of markers relative to one another based on recombination frequencies.
Genetic Maps What do you need to make a genetic map? Polymorphic markers Genotypes of individuals at a given set of markers What units are used to measure genetic distance? Centimorgans
Calculating Genetic Distance X X B b B b a A A a a A a A X X B b B b B b B b Recombinant Parental Recombinant Parental
Calculating Genetic Distance X X B b B b B b B b Recombinant Parental Recombinant Parental 73 77 21 129 73/150 = 0.49 0.49 x 100 = 49 cM 21/150 = 0.14 0.14 x 100 = 14 cM What is the highest cM value? Why fewer recombinants?
Other Considerations Which mapping function should you use? Haldane and Kosambi are the most popular Haldane corrects for double crossovers (which can’t be detected using recombination data alone) Kosambi corrects for double crossovers AND interference (the physical space required for one crossover prevents another crossover from occurring in close proximity) What is the maximum distance between pairs of markers that should be used to consider two markers “linked”? The paper used 50cM or less. What do you think?
Mapping Software Calculating recombination ratios for hundreds of markers is extremely complex! Several software tools are available Joinmap – great software but expensive QTL Cartographer R/qtl
QTL Cartographer & R/qtl R/qtl has a great tutorial for constructing a genetic map: http://www.rqtl.org/tutorials/geneticmaps.pdf Let’s See a Demo!
This powerpoint, the sample data files, and the R code can be found on the journal club wiki. http://ala.genomics.purdue.edu/User:amorales/Plant_Breeding_and_Genetics_Journal_Club Any questions?