The causal sequence of meiosis
• . i . • pro6eeds"., and where crossing-over takes place. These prime wriables ..at6 ghe.eontaet-point, the th~e-lhnit of pairing and. the torsion in paired regions. Their action has been inferred from the comparison of pairing in ~dated forms witt{ variabie pairmg frequencies and ohiasma distribution ; from ~he pa.h-ing in hybrids, mutants and po]yploids; and h'om the ~ifieiaI !n}errnption of normal pairing. Suc]a comparisons have to be m~de ~vifla even ~ea te r accuracy and detgii if gee theory of meiotic p~mng.as to be ~ested and consolidated. The time has now arrived for an exac$ definitio~ of the individual aoti.ons and of the interactions of the t~{'egva.riables and of {Heir effect onohiasma formatim.~. k it}~iJ.y of pagfing variM;ion rest~Ith~g from genetic aad :from en~dr0nmental Souzces, i o an interspeeitie eo.mparison wibh varied environmental eoi~Ntigns,i.forms ~ahe most promising approach. ~,r,gt~igcvria., which h.a,s proved such Useful material in the discovery of ~he ele.me~lts o:[ mitosis and . . . . meiosis, is eminent.]y st~ita, ble :for further ana.].gsis} :[or the following rea.soJ.is:
Fritillaria Meleagris: Chiasmaformation and distribution
Summary1.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.
Instrumentation and Automated Photometric Titration Procedure for Total Acidity Determination in Red Wine Employing a Multicommuted Flow System
An automated procedure for photometric titration of red wine and associated instrumentation is described. The procedure was based on the flow-batch approach implemented employing multicommutation. The photometric detection was carried out using a homemade LED-based photometer. The mixing device, LED, and photodetector were attached to the titration chamber in order to form a compact and small-sized unit. The flow system comprised an automatic injector and three-way solenoid valves, which were controlled by a microcomputer through an electronic interface card. The software, written in Quick BASIC 4.5, was designed with abilities to accomplish all steps of the titration procedure including data acquisition and real-time processing to decide about the course of titration in the following step and so forth, until the titration endpoint was reached. The usefulness of the proposed titration system was demonstrated by analyzing red wine samples. When results were compared with those obtained using the AOAC reference method, no significant difference was observed at the 95% confidence level. A relative standard deviation of ca  2% (n=9 ) was obtained when processing a typical red wine sample containing 7.3 gl -1 total acidity expressed as tartaric acid.