Provided that there is no chromatid interference, no movement of chiasmata, and no discrepancies between meiotic and mitotic chromosome lengths, then genetic maps and recombination fractions may be directly derived from our meiotic chiasma distribution data. This is illustrated by male chiasma derived genetic lengths and recombination fractions along chromosome 13. The recombination fraction be...

Tumours arising in the small area at the base of the brain between the optic chiasma and cerebral peduncles are common and include meningiomas, suprasellar and pituitary neoplasms, aneurysm of the circle of Willis, and chiasmal arachnoiditis with cyst formation. Tumours arising in the optic chiasma and nerve sheaths, however, are very uncommon. In all these conditions, visual symptoms may obtru...

N tetraploids the degree of multivalent formation at meiosis is often used as a 'wit erion of homology between the chromosome sets and gives information on the genetic control of chromosome association. Where the chiasma frequency of each association can be recorded in a number of cells, the observed association frequencies could be profitably compared with frequencies expected, assuming they a...

WHEREAS from the myelo-architectonic point of view the chiasma is merely an organ of transit, this is not so from the vascular point of view; there seems to be a partial dissociation between the myelo-architecture and the angio-architecture. The vascularization of the chiasma has been investigated on the basis of 22 human specimens. The techniques used (dissection after fixation in 10 per cent....

Cytological analysis of microsporogenesis in 72 popcorn plants, comprising nine from the original population (CMS-43, S(0)) and 63 from seven cycles of self-fertilization (S(1) to S(7)), one plant of S(0) generation (plant 2) was identified with B chromosomes. The number of B chromosomes varied from two to three in the same anther. The pattern of chromosome pairing and meiotic behavior of Bs we...

Natural variation in meiotic recombination frequency in Arabidopsis thaliana has been assessed by analyzing chiasma frequency variation among a range of geographically and ecologically diverse accessions. Fifty pollen mother cells at metaphase I of meiosis were analyzed from each of eight accessions and fluorescence in situ hybridization was applied to enable identification of all 10 chromosome...

The shared organization of three optic lobe neuropils-the lamina, medulla, and lobula-linked by chiasmata has been used to support arguments that insects and malacostracans are sister groups. However, in certain insects, the lobula is accompanied by a tectum-like fourth neuropil, the lobula plate, characterized by wide-field tangential neurons and linked to the medulla by uncrossed axons. The i...