laughnan: nature of mutations 9 



ence or absence of aborted pollen, the former of which is typically 

 associated with plants that are heterozygous for the translocation. 

 This classification was confirmed by scoring the ears of exceptional 

 individuals for the aborted condition. 



The s/i-2 (shrunken— 2) factor which produces a striking collapse 

 of the mature endosperm is distal to A and, whenever possible, because 

 of its close proximity to the latter, has been used as a marker in 

 preference to et (etched endosperm, virescent seedling). 



Table 1 summarizes tests of over a million gametes from A h -P /a 

 heterozygotes marked with T and sh. The A b — P alleles designated 

 Lima and Cusco are extractions from two different plants of Peruvian 

 origin and have been treated as separate entities throughout this 

 presentation. Referring to the alpha derivatives in Table 1, we note 



Table 1. — Constitutions of Alpha-bearing Strands from A h -P/a Individuals 



Marked with T and sh. 



*As illustrated by the strand constitutions provided in the first row of this table, here and in 

 similar tables to follow, nco-1 refers to a strand carrying the nonrecombinant parental markers of 

 the parental A b -P chromosome; nco-2 refers to a strand carrying the parental markers of its homo- 

 logue; co-1 refers to a recombinant strand that carries the distal marker of the parental A b -P chromo- 

 some and the proximal marker of its homologue; and co-2 refers to a recombinant strand that 

 carries the proximal marker of the parental A b -V chromosome and the distal marker of its homologue. 



that only two of the four possible marker combinations are repre- 

 sented among these strands. One of these, the recombinant type 

 designated co-1, carries the shrunken marker of the parental A b -P 

 chromosome and the T marker of the homologue. Since this recom- 



