The Cytological Identification of the Chromosome Associated with the R-G Linkage Group in ZEA MAYS.

Genetic investigations with Zea mays have established ten linkage groups. Likewise, cytological investigations have revealed the presence of ten morphologically identifiable chromosomes composing the haploid complement (MCCLINTOCK 1929b). It is the aim of the present investigation to correlate a particular linkage group with a particular chromosome. The method employed has been to obtain 2nfl plants trisomic for different members of the haploid complement, and then, by means of trisomic inheritance, to determine which chromosome carries a particular group of genes. The 2nf 1 plants have been obtained from the progeny of one original triploid (MCCLINTOCK 1929a). The chromosome-number in the female gametes of a triploid varies from ten to twenty. Trisomic individuals were obtained directly from theFr of a cross triploid X diploid and from the 2nf 1 progenies of FI individuals with more than one extra chromosome. Inheritance data obtained from the 2nfl plants of culture 131 suggested that in this culture the r-g carrying chromosome was present in triplicate. An effort was therefore made to test the validity of this interpretation and to verify the genetic inference that the nine other linkage groups are independent of the r-g chromosome. The evidence indicates that the smallest chromosome of the haploid complement carries the genes of the r-g linkage group. Thus, 2n + 1 plants of culture 131 showing trisomic inheritance for r have the smallest chromosome in duplicate in their 11-chromosome microspores. Likewise, 2nfl