Molecular Genetics of Prokaryotes Problem Set

Problem 6: Different alleles for a bacterial genes

Tutorial to help answer the question

How many lac Z genes were present in the cells described in problem 5 that were able to grow on minimal media?



The female bacterium in the conjugation experiment described in problem 5 had a beginning genotype of lac Z met bio. The lac Z locus on the bacterial chromosome is a mutant allele. Following conjugation and transfer of a copy of the F' episome, the new genotype of the recipient bacterium is still lac Z met bio on the bacterial chromosome, but now with a Plac O lac Z DNA sequence on the episome. This recombinant genotype is now diploid for the lac Z locus.

Note that partially diploid bacteria can be used to study the dominance/recessive relationships between different alleles of a gene. In this case, cells that are lac Z/lac Z are able to metabolize galactose, establishing that lac Z is dominant to lac Z as expected.

The Biology Project
University of Arizona
Thursday, October 24, 1996
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