Fri Spr W2 - Principles of Genetic Analysis (Lec2) Explain how a mutagenesis screen can be used to identify the genes required for a particular function Mutagenesis screens good way to determine genes as: 1) No previous assumptions made 2) So don't need to know underlying physiological / biochemical systems or molcs involved 3) One screen finds multiple mutant genes which can be characterised 4) The mutant genes can be investigated deeper to find genes that are related / have interacted Carry out a complementation test and interpret the findings Complementation test - A test done to determine no. of genes that determine phenotype: - Obj is to find the no. complementation grps (cos = no. mutated genes) - Find no. alleles by no. mutants (cos both are = ) - Repeat test to: 1) Identify more alleles 2) See if more compl. grps Method 1) Cross mutant breed with wild type breeds (to check mutant is recessive - cos test only works with recessive mutants) red mutant a mutant b mutant c mutant d mutant e mutant f wild-type red red red red red red Crossing the mutants to wild-type reveals that all the mutations are recessive to wild-type (because the F1 progeny has a wild-type phenotype) white Complementation tests require recessive mutations - dominant mutations cannot be used in complementation tests 2) Cross specific mutant with itself - predicted to get progeny with same mutant phenotype as parents
- Done as a control - confirms both stocks breeding faithfully and phenotype scored correctly mutant a mutant b mutant c mutant d mutant e mutant f wild-type red red red red red red mutant a white mutant b white mutant c mutant d When each mutant is crossed to the same mutant, the F1 progeny has a mutant phenotype This confirms that the both the stocks of mutants are breeding faithfully and the phenotype is scored correctly mutant e white mutant f white 3) Cross recessive mutants with each other: - if same mutant phenotype is displayed then means identified different mutation but on same gene (DO NOT COMPLEMENT EACH OTHER!) - If wild type phenotype displayed then identified different mutation on different genes (COMPLEMENTATION OCCURRENCE -> found new compl. grp!) - Mutant is said to complement another mutant if crossing it results in a progeny w/ wild type phenotype mutant a mutant b mutant c mutant d mutant e mutant f wild-type red red red red red red mutant a white red red white white red mutant b mutant c mutant d Even though these mutants have the same phenotype they produce a wild-type phenotype in the F1 - this is mutant e complementation and happens because the mutations responsible occur in different genes mutant f When mutant a is crossed to mutant d or e, the F1 progeny has a mutant phenotype When mutant a is crossed to mutant b, c or f, the F1 progeny has a wild-type phenotype white
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