Fritillaria Meleagris: Chiasmaformation and distribution

Abstract

1. Fritillaria Meleagris has twelve pairs of chromosomes, two with median, ten with more or less snb-terminal attachment constrictions. One pair has a second constriction. 2. At diplotene in the prophase of meiosis chiasrnata are not formed at random but with a greater frequency in the neighbourhood of the attachment constriction. The two chromosome types are therefore distinguishable at this stage by the distribution of their chiasmata. 3. There is no definite change in the relationships of the chromatids (i.e. no movement of chiasmata) between diplotene and metaphase. 4. The great contraction of the chromosomes conceals the details of their relationships, at least in polar views of metaphase, but it has been possible to make a small statistical study of the frequency of chiasmata from side views (see Table I). This, and the separation at anaphase, corroborate the chiasma interpretation of the structure of the bivalent chromosomes at metaphase. 5. It follows that chromosome behaviour at meiosis must be examined in relation to the possibility of differential frequency of chiasmata as well as of their movement after formation. A knowledge of both these circumstances is necessary before one can consider the analogy with crossing-over results in a particular species. 6. In the related speciesFritillaria imperialis chiasmata are formed at random. An account of behaviour in this species will appear later. 7. The bearing of this work on theOenothera problem is indicated.