In this chapter, we have focused on genetic systems present in bacteria and on the viruses that use bacteria as hosts (bacteriophages). In particular, we discussed mechanisms by which bacteria and their phages undergo genetic recombination, which allows geneticists to map bacterial and bacteriophage chromosomes. In the process, we found many opportunities to consider how this information was acquired. From the explanations given in the chapter, what answers would you propose to the following questions? How do we know that in bacteriophage T4 the rII locus is subdivided into two regions, or cistrons?

Key Concepts

Cistrons

Cistrons are segments of DNA that correspond to a single gene or functional unit within a genetic sequence. In the context of bacteriophages like T4, cistrons are crucial for understanding how specific traits or functions are encoded. The subdivision of a locus into cistrons indicates that multiple genes can exist within a single genetic region, each contributing to the overall phenotype of the organism.

Genetic Recombination

Genetic recombination is a process by which genetic material is exchanged between different organisms or within the same organism, leading to new genetic combinations. In bacteriophages, this can occur through mechanisms such as transduction or transformation, allowing for the mapping of genetic loci like the rII locus in T4. Understanding recombination is essential for deciphering how traits are inherited and expressed in bacterial and viral systems.

Mapping Genetic Loci

Mapping genetic loci involves determining the positions of genes on a chromosome and understanding their relationships to one another. In bacteriophage T4, researchers use recombination frequencies to infer the distances between cistrons within the rII locus. This mapping is vital for geneticists to predict phenotypic outcomes and understand the genetic architecture of organisms, including how mutations can affect function.