Lecture 4 Chapter 7 Part B PDF

Lecture 4 Chapter 7-part B 7.4 What mutations tell us about gene structure Learning objectives: Describe complementation testing and how its results distinguish mutations in a single gene from mutations in different genes. Explain how Benzer’s experimental results revealed that the rII re...

Lecture 4 Chapter 7-part B 7.4 What mutations tell us about gene structure Learning objectives: Describe complementation testing and how its results distinguish mutations in a single gene from mutations in different genes. Explain how Benzer’s experimental results revealed that the rII region in bacteriophage T4 contains two genes, each composed of many nucleotide pairs. Discuss how Benzer used deletions to map mutations in the rII region. Drosophila eye color mutations produce a variety of phenotypes Do these phenotypes result from different alleles of the same gene or mutations in different genes? Early Drosophila geneticists identified a large number of X-linked recessive mutations affecting the normally red wild-type eye color. Complementation testing is an approach used for this purpose © Scott Camazine & Sue Trainor/Science Source What is complementation testing? Reveals whether two mutations are in a single gene or in different genes A complementation table for X-linked eye color mutations in Drosophila These results reveal five complementation groups (genes): Mutations in white, cherry, coral, apricot, and buff are alleles of the same gene—white (w) Mutations in garnet, ruby, vermillion, and carnation are alleles of different genes What is a gene? How the structure of a gene can accommodate different mutations? and how these different mutations can alter phenotype in different ways? Does each mutation change the whole gene at a single stroke in a particular way, or does it change only a specific part of a gene, while other mutations alter other parts? What is a gene? Seymour Benzer (mid 1950-1960s) Can recombination take place between different mutations in the same gene (intragenic recombination)? Phage T4 is a virus that infects E. coli Advantages of phage T4 for detecting intragenic recombination: Each phage can produce 100 to 1000 progeny in