The Relation Between Chromosome Constitution and Sex in the Off-Spring of Triploid Melandrium

XPEHIMENTALLY produced polyploid strains of the dioecious E plant Melnndrium dbum have been a valuable tool for the study of sex genetics in this species (for references, see WARMKE, 1946; WESTERGAAIID, 1046).The experiments have shown that the Y chromosome is male determining.Three different sections of Y have been mapped by means of spontaneous fragmentations, each section playing a distinct part in sex determination by suppressing femaleness and promoting inaleeess (WESTERGAARD, 1946; cf. also Fig. 2 in the present paper).The A ' chromosome of MeZnndrium is female determining (cf.WARMKE.1946).These conclusions are mostly based on the study of sex expression in euploid Melnndriuni strains (2 A-3 A-4 A plants)with various combinations of sex chromosomes.From crossings between triploids it is possible to obtain plants with amuploid autosome numbers and different combinations of sex chromosomes.The sex expression in such plants might give interesting information with respect to the significance of the autosomes in sex determination.The results of triploid A4 elancirium cros,sings have earlier been published by WARMKE and BLAKESLEE (1940).Since these authors obtained male and female plants only in the aneuploid material, they concluded (cf.WARMKE, 1946) that the autosomes are of no importance in the mechanism of sex determination of' Melnndrium.The present paper deals with the Danish progeny of triploid Melnndrium crossings.The results described are strikingly different from those obtained by the American authors, and the material does not support the statement that the autosomes are insignificant for the sex determination of this species.The investigations were carried out at the Iaboratory of Genetics of the Agricultural College, Copenhagen. Iferedifne S'.