Question

Suppose we were successful in identifying 12 mutants using a screen for identifying conditional mutants of S. cerevisiae in which the secretory system was defective. Part A Describe the crosses you would perform to determine the number of different genes represented by the 12 mutations. Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Terms can be used once, more than once, or not at all.
a. dominant
b. permissive
c. mutant
d. codominant
e. wild type
f. restrictive
g. recessive
Each mutant would be mated to ___ and to every other ____ to create diploid strains. The diploids would be assayed for growth at____ and restrictive temperature. Diploids formed by mating a mutant to a ____ that can grow at ____ temperatures identify the mutation as____ . Only ___ mutations can be studied using complementation analysis. Diploids formed by mating two ___ mutants identify mutations in the same gene if the diploid cannot grow at ___temperature (non-complementation), and they identify mutations in different genes if the diploids can grow at____ temperature (complementation).

Answer 1

Answer:

Each mutant would be mated to wild type and to every other mutant to create diploid strains. The diploids would be assayed for growth at permissive and restrictive temperature. Diploids formed by mating a mutant to a wild type that can grow at restrictive temperatures identify the mutation as recessive. Only recessive mutations can be studied using complementation analysis. Diploids formed by mating two recessive mutants identify mutations in the same gene if the diploid cannot grow at restrictive temperature (non-complementation), and they identify mutations in different genes if the diploids can grow at restrictive temperature (complementation).

Explanation:

Recessive mutations are those whose phenotypic effects are only visible in homo-zygous individuals. Moreover, a complementation test is a genetic technique used to determine if two different mutations associated with a phenotype colocalize in the same locus (i.e., they are alleles of the same gene) or affect two different loci.  In diploid (2n) organisms, this test is performed by crossing two homo-zygous recessive mutants and then observing whether offspring have the wild-type phenotype. When two different recessive mutations localize in different loci, they can be considered as 'complementary' since the heterozygote condition may rescue the function lost in homo-zygous recessive mutants. In consequence, when two recessive mutations are combined in the same genetic background (i.e., in the same individual) and they produce the same phenotype, it is possible to determine that both mutations are alleles of the same gene/locus.