Questions and Problems 543 



5. Two populations of the same species are 2000 miles apart. Over 

 a long period of time, nmnerous small mutations accumulate, many of 

 which affect the same characters. After a considerable period, they 

 differ with respect to plant height, corolla size, seed weight, and the 

 lengths of the leaves. These differences are noticeable but not great, but 

 all are the result of multiple genes. Should the two new populations be 

 classed as new species? Would your answer be the same if, in addition 

 to these differences, they also produced hybrids that were partially or 

 completely sterile? Explain. 



6. Would your answer to question 5 be different if, instead of differ- 

 ing in those quantitative characters, the two populations differed with 

 respect to opposite or alternate leaves, bicarpellate or tricarpellate 

 ovaries, and pubescent or glabrous leaves, assuming that each of these 

 three character differences is determined by a single pair of alleles? As- 

 sume both sterility and nonsterility of the hybrids. 



7. Oenothera hiennis is composed of two complexes, albicans and 

 rubens, but breeds true. When it is crossed with Oe. Hookeri, it 

 forms two types of plants (twin hybrids), albicans • ^Hookeri and 

 rubens • -'Hookeri. Explain. If selfed, both these twin hybrids produce 

 two types of progeny in their offspring. What would they be, and in 

 what ratios? 



8. Oe. Lamarckiana has the complexes gaudens and velans, and 

 Oe. chicaginensis has punctulans and excellens. The cross Lamarck- 

 iana X chicaginensis gives two types of plants, gaudens • punctulans and 

 velans • punctulans, and the reciprocal cross gives excellens • gaudens 

 and excellens • velans. However, when Lamarckiana is crossed with 

 Oe. grandiflora, which has acuens and truncans, four types are found, 

 gaudens • acuens, velans • acuens, gaudens • truncans, and velans • trun- 

 cans. Explain. 



9. The segmental arrangement in the complex ^Hookeri is 1 • 2, 3 • 4, 

 5 • 6, 7 • 8, 9 • 10, 11 • 12, 13 • 14. Complex flavens differs from it only 

 in having 1*4, 3*2 instead of 1*2, 3*4. Complex velans differs 

 from ^Hookeri in having 5*8, 7*6; acuens differs from it by 1 • 4, 

 3-2, 7-10, 9-8; and ^Johansen is different by 7 • 10, 9 • 8. All 

 other chromosomes in these complexes are the same as in ^Hookeri. 

 How many circles and pairs would be found in all the possible combi- 

 nations of two of those five complexes? 



10. Red flower color (W) is dominant to white (w). Ten WW and 

 one WW plant became established on an isolated island. If complete 

 freedom of crossing and complete \4ability of offspring were assumed, 

 what would be the composition of the plants on the island after three 

 generations ? 



