I H, ( H M-l IR 10 



1 ou is. K. R.. and John. B.. Chromosome Murker. 1 omlnn. I. and A. Churchill. 1 td., 

 1963. 



Sturtevant, A H.. "The 1 inear Arrangement ol Six Sex-Linked I actors m Drosophila. 

 .^ Shown bj I hen Mode oi Association," I. Exp. Zool., 14:43 59, 1913. Re- 

 printed in Classic Papers in Genetics, Peters. I. A. (Ed.). Englcwood Cliffs, N.J.: 

 Prentice-Hall. 1959, pp. 67-78. 



See Supplement II. 



QUESTIONS FOR DISCUSSION 



10.1. Does the linear arrangement ol the -cues offer anj evidence for or against the 

 hypothesis that chromosomes are carriers of genes? Explain. 



10.2. How many gene pairs must he heterozygous lor you to detect a single and a 

 douhle crossover in Drosophila? In Neurospora? 



10.3. Suppose a pair of homologs in Neurospora have the genotypes A B/a b. Draw 

 an eight-spore ascus derived from a cell that had: 



(a) No chiasma hetween these homologs 



(h) One chiasma between the centromere and the gene pair closest to it 



(c) One chiasma between the two pairs of genes 



(d) One two-strand double chiasmata between the two pairs of genes 



10.4. What are the advantages of Neurospora over Drosophila as material for genetic 

 studies? 



10.5. Under what conditions would segregation ol a pair ol' alleles occur during the 

 first meiotic division? The second meiotic division? 



10.6. What indications might you have that differential viability plays a role in modify- 

 ing experimentally obtained crossover distances? 



10.7. How many linked loci must be hybrid in a Drosophila individual and a Neuro- 

 spora individual to determine from crossover data whether these loci are ar- 

 ranged linearly? Explain. 



10.8. A test cross proves that one of the parents produced gametes of the following 

 genotypes: 42.4% PZ, 6.9% Pz; 7.0% pZ\ and 43.7% pz. List all the genetic 

 conclusions you can derive from these data. 



10.9. The trihybrid Aa Bb Cc is test crossed to the triple recessive, aahbec, and the 

 following phenotypic results are obtained: abc 64; abC 2: aBc 11; aBC 18; AbC 

 14; Abc 17; ABc 3; ABC 71. 



(a) Which of these loci are linked? Why? 



(b) Rewrite the genotypes of both parents. 



(c) Determine the observed map distances between all the different pairs of 

 linked genes. 



10.10. A Drosophila female with yellow body color, vermilion eye color, and cut 

 wings is crossed with a wild-type male. In F t all females are wild-type and 

 males are yellow, vermilion, cut. When the F, are mated to each other, the F L , 

 are phenotypically as follows: 



1781 wild-type 1712 yellow, vermilion, cut 



442 yellow 470 vermilion, cut 



296 vermilion 265 yellow, cut 



53 cut 48 yellow, vermilion 



Construct a crossover map for y, v, and ct from these data, giving the map 

 distances between loci. 



