Maps & DNA Sequencing – Lecture notes 18 – GEN 604 – Principles Of

Genetic Maps

– Maps display gene order and distance between genes

– Map distance is derived from recombination frequency in eukaryotes or interrupted mating

experiments in prokaryotes

– Recombination is not always directly proportional to distance

– Genetic maps can be made for eukaryotes or prokaryotes (even for some viruses)

– Genes to be mapped must be identifiable by observing a phenotype or by measuring a

characteristic

– Difficult/impossible to determine what type of DNA changes occurred to create a mutant

organism

Physical Maps

– Based on the actual DNA sequence, not recombination

– Map distances are exact to a single base pair

– Maps can be made for any organism, living or dead, if enough genomic DNA can be obtained

– Genes and their mutations can be identified without having a mutant phenotype or measuring any

characteristics

– May be difficult to predict what process a gene might be involved in and what a mutant

phenotype might look like

E.coli Genetic Map (circa 1963)

– Map based on interrupted mating experiments and distance is measured in minutes (size of E.coli

genome = 900 min)

– ~100 genes on map because mutations in those genes resulted in phenotypes

– Only 5 minutes of 90 minutes is shown

– ~100 genes in ~6% of the genome

– New techniques provided information about whether gene is on top of strand of DNA or bottom

strand