Sex Chromosomes in the Hop Humulus lupulus

Abstract

STUDIES of meiosis in male plants of the hop Humulus lupulus have resulted in conflicting reports on the nature of the sex chromosomes. Winge¹ and Jacobsen² have described an unequal pair of sex chromosomes which Jacobsen also identified in the somatic cells of male and female plants. Sinoto³ found no heteromorphic pair, but described a chain of four sex chromosomes which he designated X ₁ Y ₁ X ₂ Y ₂. No evidence was put forward in support of this interpretation. Ono⁴, however, demonstrated in H. lupulus var. cordifolius (the wild hop of Japan) that a quadrivalent occurred in meiotic divisions in the male, but not in the female plant. More recently⁵ he has described the occurrence, in a number of male varieties, of five different sex chromosome types, one of which is a homomorphic pair, two are heteromorphic pairs with different length ratios, and two are complexes of four chromosomes, also with differing length ratios.