background: we describe karyotypic variations and the in vitro methods for plant propagation and conservation as well as detailed chromosomal analysis of (aloe vera l.) and aloe littoralis from iran during flowering stage. objectives: this karyotypic was discovered because of a difference in the position of the chromosome and due to genomic differentiation in domesticated populations of the ira...

Chiasmata in diplotene bivalents are located at the points of physical exchange (crossing-over) between homologous chromosomes. We have studied chiasma distribution within chicken lampbrush chromosome 1 to estimate the crossing-over frequency between chromosome landmarks. The position of the centromere and chromosome region 1q3.3-1q3.6 on lampbrush chromosome 1 were determined by comparative ph...

In juvenile Xenopus retinotopic fibre order in the optic tract near the chiasma was investigated by labelling small groups of optic fibres from peripheral retina with HRP. This selective fibre labelling with HRP was combined with autoradiography following administration of tritiated thymidine to the eye, so that the HRP-labelled fibres could be located within the borders of the optic tract. Fib...

It is often convenient to define models for the process of chiasma formation at meiosis as stationary renewal models. However, count-location models are also useful, particularly to capture the biological requirement of at least one chiasma per chromosome. The Sturt model and truncated Poisson model are both count-location models with this feature. We show that the truncated Poisson model can a...

Presynaptic association of homologous chromosomes is a prerequisite to the sequence of events that lead to chiasma formation. This association of homologous chromosomes, as entire units, occurs with probability a, and chiasma formation occurs independently in opposite chromosome arms with probability c. a and c have been estimated from frequencies of different chromosome configurations at metap...

A single chromosome of the grass species Festuca pratensis has been introgressed into Lolium perenne to produce a diploid monosomic substitution line 2n = 2x = 14. The chromatin of F. pratensis and L. perenne can be distinguished by genomic in situ hybridization (GISH), and it is therefore possible to visualize the substituted F. pratensis chromosome in the L. perenne background and to study ch...

Thirty patients with chiasma syndrome attributed to ischemic processes of various origins are described. The initial diagnosis was made after an investigation based on polytome pneumoencephalography and angiography. This diagnosis was confirmed later with the use of high-resolution computed tomography (CT) and refined angiographic techniques. The ischemic chiasma syndrome may be classified into...