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


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


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


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


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