SHOKTER ARTICLES AND DISCUSSION 



LINKAGE IN MAIZE : THE C ALEURONE FACTOR AND 

 AY ANY ENDOSPERM 1 



In 1912 Collins 2 presented data which showed a linkage be- 

 tween waxy endosperm and aleurone color in certain hybrids of 

 Chinese and American corn. A summary of the F 2 data in Table 

 II, p. 579, 2 gives the coefficient of association as .821. This is 

 equivalent, approximately, to a 3.5-1 gametic ratio, and a cross- 

 ing-over percentage of 22. The percentage of waxy grains is 

 about 21 and colorless about 25. This is good evidence that 

 Collins is dealing with material heterozygous for waxy endo- 

 sperm and heterozygous for only one factor in aleurone. In the 

 back cross data in Collins 's Table IV none of the ears shows the 

 1 : 1 relation between colored and colorless expected from plants 

 heterozygous for one color factor. The material in that table 

 apparently involves more than one aleurone factor in the het- 

 erozygous condition and before such data may be considered in 

 any linkage study they must be corrected for this or the true 

 values for the percentage of crossing over can not be ascertained. 

 The coefficient of association need not be used if we are dealing 

 with back cross data. If it seems desirable to use the coefficient 

 of association with this sort of data new tables should be calcu- 

 lated from the gametic series n : 1 : 1 : n corrected for the respec- 

 tive aleurone factor conditions. 



The advantage of back cross data is obvious. Data of this 

 nature obtained by the writer from crosses of plants heterozygous 

 for one aleurone factor and for waxiness with double recessive 

 plants are presented in the table on p. 58. 



Families 6, 99, and 100 are derived from colored corneous 

 seeds heterozygous for aleurone and waxiness. Families 9 and 

 101 are colorless waxy plants. The first nine ears give an average 

 crossing over of 26.7 per cent, or a gametic ratio of 2.75 : 1. Ears 

 8 and 9 show repulsion instead of coupling, but this does not 



1 Paper No. 66, Department of Plant Breeding, Cornell University, Ithaca, 

 N. T. 



2 "Gametic Coupling as a Cause of Correlations," Amer. Nat., 46, pp. 

 569-590. 1912. 



