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

Maps & DNA Sequencing - Lecture notes 18

Principles Of Genetics (GEN 604)