Joel Sohn

Joel Sohn
Harvard University | Harvard · Faculty of Arts and Sciences

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16
Publications
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Publications

Publications (16)
Article
The skate, a cartilaginous fish related to sharks and rays, possess a unique electrosensitive sensory organ known as the ampullae of Lorenzini (AoL). This organ is responsible for the detection of weak electric field changes caused by the muscle contractions of their prey. While keratan sulfate (KS) is believed to be a component of a jelly that fil...
Article
Full-text available
In 1678, Stefano Lorenzini first described a network of organs of unknown function in the torpedo ray-the ampullae of Lorenzini (AoL). An individual ampulla consists of a pore on the skin that is open to the environment, a canal containing a jelly and leading to an alveolus with a series of electrosensing cells. The role of the AoL remained a myste...
Article
Full-text available
Chitin, a biopolymer of N-acetylglucosamine, is abundant in invertebrates and fungi and is an important structural molecule [1, 2]. There has been a longstanding belief that vertebrates do not produce chitin; however, we have obtained compelling evidence to the contrary. Chitin synthase genes are present in numerous fishes and amphibians, and chiti...
Chapter
Efforts to understand strongly interacting Fermi systems using generalizations of the Gutzwiller variational wavefunction are described. An extended Hubbard model with strong intersite repulsions on a two-dimensional copper-oxygen lattice has a charge transfer instability that is studied using the method, and the possibility that this model has a g...
Article
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Article
Two anatomically distinct neuronal GRF systems in the brain-pituitary of the teleost codfish (Gadus morhua), immunohistochemically localized by use of antisera directed against hpGRF1-44NH2 and hpGRF1-40OH are described. Chromatographic analysis additionally revealed the presence of three molecular variants of immunoreactive hpGRF1-44NH2, two of wh...
Article
Full-text available
In order to elucidate the relationship between age, weight, genotype and sexual maturation, we raised male platyfish, Xiphophorus maculatus, of two "maturation" genotypes under a wide variety of environmental conditions. In spite of enormous variation in the ages and weights at sexual maturation, the two maturation genotypes produced phenotypes tha...
Article
Acetic acid extracts of codfish brain contain three different immunoreactive (IR) luteinizing hormone-releasing hormone (LH-RH) like materials which differ from the mammalian LH-RH decapeptide by their behavior on chromatographic separation (molecular sieving, ion exchange and high performance liquid chromatography), and their reaction with two wel...
Article
There are three sex chromosomes, W, X, and Y, found in almost all populations of the platyfish, Xiphophorus maculatus. The female genotypes are WY, WX, and XX while the males are XY and YY. We present a mathematical model to describe the changes in frequencies of these genotypes. The conditions for stability of this polymorphism are that the fitnes...
Article
The mayapple, Podophyllum peltatum (L.), is an herbaceous, rhizomatous perennial growing in the deciduous woods of the eastern USA. It is possible, by examination of the rhizome, to determine the incidence of sexual or asexual reprdocution in previous seasons. We deomonstrate that a good predictor of sexuality is the size of the preceding internode...
Article
Full-text available
A single sex-lined gene that controls the maturation process had previously been identified in Xiphophorus maculatus. It was presumed that this gene controls the age of onset of maturation. We demonstrate that the gene is either activated or not inhibited from activity by the attainment of a critical weight rather than age.
Article
Krumholz (1963) proposed that predation and competition affected the survivorship and fertility schedules of Gambusia manni at Bimini, Bahamas. He showed that in predator exposed populations the sex ratio was lower, no senile individuals were present, the number of offspring per brood was higher and that in males there was a definite shift in the s...
Article
Maturation in Xiphophorus maculatus (Pisces; Poeciliidae) is under control of the sex-linked P gene. However, when two individuals are reared together the socially dominant individual delays the maturation of the subordinate. Nevertheless, it is not a requirement that a fish be socially dominant to become mature. The data suggest that inhibition of...
Article
Entire colonies of Stylophora pistillata and Acropora variabilis were collected along a depth transect 100 m south of the Marine Biological Laboratory of Hebrew University Elat, Israel. The branch height of Acropora variabilis decreases significantly with respect to depth, and this species is equitably distributed from 5 to 30 m. Stylophora pistill...

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