COLOR FACTORS IN BEAN HYBRIDS 



Karl Sax 



Maine Agricultural Experiment Station 



And 



H. C. McPhee 



Bussev Institution of Harvard University 



THE GENETIC results of bean 

 breeding experiments which have 

 been carried on at the Maine 

 Agricultural Experiment Station for 

 the past ten years are. in most cases, 

 in accord with the results of previous 

 investigators. Pigmentation of seed 

 coat is dependent on a factor P. the 

 recessive of which results in white 

 beans. Mottling has been attributed 

 to two factors in the same linkage 

 group, both of which are necessary to 

 produce mottling. Either mottling fac- 

 tor may exist independently in uni- 

 formly pigmented beans and when 

 brought together by such parents result 

 in mottled beans which do not breed 

 true. However, some rather unusual 

 results have been obtained with eyed 

 beans. 



The behavior of certain crosses of 

 eyed beans is of considerable interest 

 in regard to allelomorphic relationships. 

 The parents used are known under the 

 rather local names of Old Fashioned 

 Yellow Eye (0. F. Y. E.) and Im- 

 proved Yellow Eye (/. Y. E.) The 

 type of eye pattern of each variety 

 is well illustrated in Figure 8. In 

 the O. F. Y. E. the pigmented area 

 covers about one-sixth of the surface 

 of the seed, while in the /. Y. E. about 

 one-fourth of the bean is pigmented. 



The cross O. F. Y. E. X /. Y. E. 

 results in "Piebald" beans in the first 

 generation which have over twice as 

 much pigmented surface as is found 

 in either parent. This type of eye 

 is irregular in outline and is accom- 

 panied by circular areas of pigment 

 on the side of the bean opposite the 

 hilum. In the second generation the 

 segregation is 1 0. F. Y. E.: 2 "pie- 

 bald" : 1 I. Y. E., indicating that only a 



single pair of allelomorphic factors are 

 involved. The actual second generation 

 segregates gave approximately 1 :2 :1 

 ratios, but in order to get larger num- 

 bers the second generation "piebald" 

 beans were carried to the third genera- 

 tion. The behavior of these third 

 generation segregates is shown in 

 Table 1. 



Each second generation "piebald" 

 segregate was planted separately and 

 in every case their progeny in the third 

 hybrid generation segregated into /. 

 Y. E., 0. F. Y. E., and "piebald." 

 The numbers of segregates in each 

 class is a very good fit for a 1 :3 :1 

 ratio as indicated by the probable er- 

 rors. The test for goodness of fit 

 gave a value of P = .8. 



The "piebald" character is rather va- 

 riable, but seeds from the same plant 

 are just as variable in pattern as seeds 

 from diiterent plants. In some cases 

 the pigment is extended over almost 

 the entire bean so that less than ten 

 per cent of the seed coat is white. 

 In no case did the piebald segregates 

 breed true. The eye pattern of the 

 eyed segregates varied somewhat in 

 the second and third generations, but 

 there was no difficulty in classing the 

 segregates as O. F. Y. E. or /. Y. E. 

 Over 300 such parental segregates were 

 planted and not one failed to breed 

 true. 



It is evident that only a single pair 

 of allelomorphic factors are involved 

 in this cross. When these factors are 

 in the heterozygous condition the pig- 

 mented area is more than doubled as 

 compared with the parents and the eye 

 pattern is not intermediate nor does it 

 resemble the pattern of either parent. 

 Usually a single pair of allelomorphic 



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