FINITE POPULATIONS 



51 



fects. Were there no linkage all possible recombinations of 

 these 2 characters would be achieved in an F2 of reasonable 

 The 16 recombination t}^es illustrated in Fig. 9 



size. 



would, in a population of 256, be expected with the fre- 

 quencies shown in Fig. 10. In other words, there would be 

 a great many intermediate leaves more or less like the Fi 

 (AaBhCcDd), and the 4 extreme recombinations (AABB- 

 CCDD, aaBBccDD, AAbbCCdd, and aabbccdd) would be 



AACC 4 



aacc 







hbdd 



3 4 



—^BBDD 



Fig. 10. Frequencies of the leaf types shown in Fig. 9, to be expected in 



an F2 of 256 plants between an ovate-glabrous parent (0, 0) and an obo- 



vate-pubescent parent (4, 4) if there were no linkage. 



rare. All 4 of these corner extremes are equally likely to 

 appear, and all 4 are true breeding, whereas the percentage 

 of homozygosity is lowest in the center of the chart. There 

 would, therefore, be a tendency in later generations for these 

 extreme types to be more frequent, the exact results depend- 

 ing on the natural mating system, the size of the populations, 

 etc. 



If, however, genes A, B, C, D, were linked (and in that 

 order) and were close enough together so that double cross- 

 overs were either never produced or produced with such a 

 low frequency that for statistical purposes they could be dis- 

 regarded, then all the possible types of the F2 are dia- 

 grammed in Fig. 11, along with their expected frequencies in 



