CHIMERAS IN CORN HYBRIDS 



Xenia in F^ Corn Hybrids Changed Through Mutation — Chimeras in Flowers — A 



Case of Chimera in a Fig 



J. L. Collins 

 Instructor in Genetics, University of California, Berkeley, Cat. 



AMONG the purple starchy F^ 

 dent grains of corn resulting 

 from crossing Extra Early 

 Adams white dent corn with 

 Black Mexican sweet corn one grain 

 was found half of which was white, the 

 other half being the dark purple color 

 characteristic of the male parent (Fig. 

 la). The line separating the colored 

 from the uncolored area was sharply 

 defined. 



In order to determine whether there 

 is any hereditary tendency for the for- 

 mation of such "mosaics," this F^ grain 

 was planted, and the four ears shown in 

 Fig. 2 were produced. They showed 

 segregation into purple and white colors 

 and starchy and sugaiy endosperm^ 

 characters in the following proportions : 

 408 purple starchy, 352 white starchy, 

 172 purple sweet, 151 white sweet. 

 This approximates the Eg dihybrid 

 ratio to be expected from a cross of 

 white dent with purple sweet corn 

 when starchy endosperm and purple 

 aleurone- are dominant characters. 



Among the 1,083 Eg grains twelve 

 were found showing reappearance of 

 the mosaic in a degree as great or less 

 than was shown by the E^ parent. 

 There is not sufficieut evidence in the 

 way of reappearances, however, to lead 

 one to believe that the condition is in- 

 herited in a Mendelian fashion. East 

 and Hayes grew a number of such seeds 

 to see whether the tendency was in- 

 herited, but without positive results. 



Similar cases in Ej corn hybrids 

 have been noted by Correns and by 

 Webber, both of whom believed that it 

 was caused by the failure of the 



second pollen nucleus and the endo- 

 sperm nucleus to fuse, so that each 

 nucleus developed independently and 

 thus formed one-half of the endosperm, 

 which is enclosed by the colorless peri- 

 carp composed entirely of maternal tis- 

 sue. This explanation cannot hold in 

 this case, because, if such were true, 

 the purple half of the seed should also 

 have had the sweet endosperm, inas- 

 much as the factor for purple aleurone 

 and the factor for sweet endosperm 

 were carried by the same (male) nu- 

 cleus. Reference to Fig. la shows tliat 

 the entire grain had the starchy endo- 

 sperm. The Eg results show the em- 

 bryo to have been a true hybrid for 

 both aleurone color and endosperm tex- 

 ture, with the starchy endosperm, to all 

 appearances, completely dominant in 

 the Ej. If we are to believe that each 

 nucleus developed independently to pro- 

 duce the bicolored aleurone effect, how 

 can we harmonize this belief with the 

 fact of uniform dominance of the 

 starchy endosperm? East and Hayes 

 suggest that the phenomenon may be 

 due to "Mendelian ssgregation" in so- 

 matic tissue. That there is no known 

 physical basis for the operation of such 

 segregation is clearly shown by Bab- 

 cock and Lloyd where they state that 

 "the mechanism by which this (Men- 

 delian) segregation is accomplished is 

 the separation of whole chromosomes 

 in the heterotypic mitosis (meiosis) 

 during maturation of the genu cclls/'^ 

 Such separation of chromosomes does 

 not normally occur during division of 

 somatic cells. 



1 Endosperm. — The substance stored in a seed adjacent to the embryo, for its early 

 nourishment. 



2 Aleurone. — The protein granules found in the endosperm of ripe seeds. 



3 Italics are mine. 



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