Translocation 3-5d. -- T 3-5d was isolated in an early dent corn from northern Wisconsin in 1938. (Shuman, John R., A chromosomal interchange in maize giving both chain and ring configurations and low sterility. Summaries of Doctoral Dissertations, University of Wisconsin Press 4: 57-58. 1940.) The strain was not subjected to any treatments known to induce chromosomal changes.

Interchange configurations at diakinesis were examined in 239 microsporocytes from a heterozygous plant, and 225 were classified as follows: 90.6% of the cells had chains of four chromosomes; 4.4% had four chromosomes in an open ring, 3.2% had closed rings of four chromosomes and 1.8% had 10 "bivalents". These observations were interpreted as evidence of a reciprocal translocation in which a comparatively short segment had been exchanged with a longer non-homologous one.

At Anaphase 1, 79 microsporocytes from a heterozygous plant had an alternate disjunction of the chromosomes of the complex, and 97 showed an adjacent separation. These frequencies do not differ significantly from equality.

Diakinesis figures from hybrids combining the interchange under investigation with T 1-2a, T 2-9b, T 4-9a, T 6-8 had two independent complexes of four chromosomes and six bivalents; with T 3-8a and T 5-7a there was one complex of six chromosomes and seven bivalents; and with T 3-5b there was one complex of four chromosomes and eight bivalents. Hence chromosomes 3 and 5 were involved in the interchange; and it was labeled d since three T 3-5's were previously described.

Three plants heterozygous for T 3-5d had 24.4% of 2274 pollen grains aborted, and 26.8% of 1315 possible kernels missing from the corresponding ears. These two percentages do not differ significantly from each other, nor from the assumed 25% abortion.

Normal plants as the seed parent crossed with T 3-5d heterozygous resulted in 47.2% of 182 plants from two families with 25% pollen abortion. This per cent of partially sterile plants does not differ significantly from 50%, i.e. a 2 (normal) : 1 (25% sterile) plant ratio. T 3-5d heterozygous as the seed parent crossed with normal plants gave 37.4% of 251 plants from two families with 25% abortion. T 3-5d heterozygous plants sibbed produced 37.7% of 212 plants from two families with 25% abortion. Neither of the latter two distributions differ significantly from each other or from 33 1/3%, i.e. a 2 ("normal") : 1 (25% sterile) plant ratio.

It was therefore postulated that of the four equally frequent classes of spores expected in the heterozygote, only that class deficient for the longer interchanged segment is aborted. The class of spores deficient for the shorter segment but duplicate for the longer one survived through the seed - but not through the pollen parent - despite the fact that 75% of the pollen grains appeared normal. Normal plants, those heterozygous and homozygous for the interchange were morphologically indistinguishable. Plants homozygous for the translocation were completely fertile.

John R. Shuman