Gene Fine Structure So far we have been considering the phenotypic consequences of mutations in different genes and the relative positions of genes along chromosomes. Now we are going to look at the internal structure of genes themselves and to consider the different kinds of mutations that are found in genes. For the next eleven lectures we will examine the genes of bacteria and their viruses, known as phage(some special features of eukaryotic genes will come later). First, lets see how the life cycle of phage can be exploited to carry out classical genetic manipulations E coli cell DNA synthesis Phage protein expression head assembly Lysis DNA packaging pl lawn of bacteria In order to do genetics with phage it is necessary to have recognizable variants of phage The easiest mutants to work with have obvious distinctive plaque morphologies make small plaques because fewer particles are released n phage normally infects cells to make more phage. But about 1%o of the time phage becomes quiescent in host cell and prevents other phage from infecting that cell. This property of phage n is known as immunity. The quiescent pl Is known as a lysogen er mutants make clear plaques because they can't form lysogens lysogens wild-type unbid plaque clear plaqueGene Fine Structure So far we have been considering the phenotypic consequences of mutations in different genes and the relative positions of genes along chromosomes. Now we are going to look at the internal structure of genes themselves and to consider the different kinds of mutations that are found in genes. For the next eleven lectures we will examine the genes of bacteria and their viruses, known as phage (some special features of eukaryotic genes will come later). First, let’s see how the life cycle of phage can be exploited to carry out classical genetic manipulations. Phage cross In order to do genetics with phage it is necessary to have recognizable variants of phage. The easiest mutants to work with have obvious distinctive plaque morphologies λ phage mi–: make small plaques because fewer particles are released λ phage normally infects cells to make more phage. But about 1% of the time phage becomes quiescent in host cell and prevents other phage from infecting that cell. This property of phage λ is known as immunity. The quiescent phage is known as a lysogen. cI– mutants make clear plaques because they can’t form lysogens