You want to build a double mutant (ab/ab) between two linked genes that are 24 map units apart. gene a comes in two forms: the recessive mutant allele (a) or the wildtype allele (+). similarly, gene b comes in two forms: the recessive mutant allele (b) or the wildtype allele (+). you first cross single mutant a/a into single mutant b/b to create the repulsion dihybrid: a+/+b (the order i place the alleles is critical). next, you do an f1 dihybrid cross and search the f2 generation for the rare double mutant phenotype: ab/ab. 14. what is the frequency expected for the f1 gamete type, at? 15. what is the frequency expected for the fi gamete type, tb? 16. what is the frequency expected for the f1 gamete type, ab? 17. what is the frequency expected for the f1 gamete type, ++? 18. what percent of f2 progeny are expected to have the double mutant phenotype? you want to build a single mutant (a/a) from a double mutant (ab/ab). the a and b genes are 12 map units apart. gene a comes in two forms: the recessive mutant allele (a) or the wildtype allele (+). similarly, gene b comes in two forms: the recessive mutant allele (b) or the wildtype allele (+). you first cross the double mutant ab/ab into a wildtype strain (++/++) to create the coupling dihybrid: ++/ab (the order place the alleles is critical). next, you do an f1 dihybrid cross and search the f2 generation for the rare animal with the single mutant phenotype (hint: this phenotype does not just include the a+la+ genotype! it might be a good idea to write out a punnett square that includes both frequencies and genotypes). 19. what is the frequency expected for the f1 gamete type, at? 20. what is the frequency expected for the f1 gamete type, +b? 21. what is the frequency expected for the f1 gamete type, ab? 22. what is the frequency expected for the f1 gamete type, +? 23. what percent of f2 progeny are expected to have the single mutant phenotype associated with the a gene?