Questions and Problems 413 



11. What would be the chromosomal arrangement in hybrids between 

 these three types and PTl of D. stramonium (see text) ? 



12. A plant has the following chromosomes: 1-2, 3-4, 5-6, 7-8, 9*10, 

 11-12, 13-14, 15-16. It is X-rayed and an interchange occurs between 

 chromosomes 7-8 and 11-12, so that the new chromosomes are 7-12 

 and 11-8. The homozygous interchange type is later X-rayed and new 

 interchange types are produced, (a) One produces a circle of four with 

 the interchange type and only pairs with the original type; (b) an- 

 other produces a circle of four with the interchange type and two 

 circles of four with the original type; (c) a third produces a circle of 

 four with the original type and a circle of six with the interchange 

 type. What might be the interchanges that formed these three new 

 types? 



