The mutation Fused, which produces shortening and thickening of the tail, together with ankyloses of contiguous vertebrae and other abnormalities, has been studied for twenty -five generations in inbred homozygous lines and in crosses. The homozygotes show a variable expression from taillessness (in 3.4%) to normal tail (in 1.1%), which was not changed by inbreeding or selection. The normal overlaps proved to beFu/Fu, hence not recombinations. In outcrosses to normal it segregated normally as a dominant. When crossed with the similar mutant Kink(Ki) the combinationFu/Ki has a shorter tail thanFu/ +.Fu/Ki x + + gave 933Fu orKi and 52 normal. All of the latter which were tested proved to beFu/ + (orKi/ +), and the probability of recombination between Ful/Ki was shown to bep ≤0.003 with 95 % confidence coefficient. HenceFu andFuKiare assumed to be alleles.
The bearing of these facts on the constitution of the ninth linkage group which contains sets of allelesT...tn andFu,..FuKi with similar effects is discussed.
Volume 100, 2021
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