A case of linkage of sex-chromosomes with autosomes in the pollen mother cell of <i>Humulus japonicus</i>

Abstract

In the present paper a case of linkage of sex-chromosomes with autosomes is described. The observations are made exclusively from pollen mother cells of an male plant of Humulus japonicus SIEB et ZUCC. which was cultivated in Hokkaido (Northern part of Japan). This male is pure in its sexual expression, but unusual as to the behavior of sex-chromosomes. The results are summed up as follows:(1) There is one pentapartite chromosome complex in the diakinesis beside 6 normal bivalents. From the comparison of this unusual male with normal males, it is clear that this pentapartite complex is formed as the result of the end to end union of the sex-chromosomes (Y1XY2) and an autosome pair(ss). This pair of autosomes is one of the smallest elements of 7 bibalents of the normal male.(2) The multiple chromosomes are united in the order Y1 ss XY2 (Fig. 1 and 2).(3) In the heterotypic metaphase we see W- or N- shaped arrangement of the pentapartite complex (Fig. 3 and 4). From the latter arrangement two kinds of gametes are expected, namely 6+s+s+Y2 and 6+X+Y1.Very often we see modifications owing to the separation of the linked elments. In Figs. 5 and 6 two cases are shown, in each of these the complex is divided in three parts Y1, ss and XY2. In this case we can expect four kinds of gametes, namely 6+s+X, 6+s+Y1+Y2, 6+s+Y1+X and 6+s+Y2. In Figs. 7 and 8 the complex is divided in two groups Y1 s and sXY2.Further we can clearly see an unequal pair sY1, and a large pair XY2 in Fig. 9, where one s-chromosome is cut off by the knife.(4) The second division is equational. We can see two kinds of the daughter plates, one with 8 chromosomes and the other with 9.(5) Fertility of pollen grains was not studied.(6) The validity of the new interpretation of WINGE (1929) on the sex-chromosomes ofH. japonicus, that 3X's determine the male while 2X's the female, is discussed.