In Xiphophorus, the causative genetic information for melanoma formation has been assigned by classical genetics to chromosomal loci, which are located on the sex chromosomes. In our attempts to molecularly clone these melanoma-determining loci, named Tu, we have looked for restriction-fragment-length markers (RFLMs) linked to the Tu loci. These RFLMs should be useful in obtaining a physical ma...

Natural hybrid zones provide opportunities to study a range of evolutionary phenomena from speciation to the genetic basis of fitness-related traits. We show that widespread hybridization has occurred between two neo-tropical stream fishes with partial reproductive isolation. Phylogenetic analyses of mitochondrial sequence data showed that the swordtail fish Xiphophorus birchmanni is monophylet...

Male swordtails in the genus Xiphophorus display a conspicuous ventral elongation of the caudal fin, the sword, which arose through sexual selection due to female preference. Females mate regularly and are able to store sperm for at least 6 months. If multiple mating is frequent, this would raise the intriguing question about the role of female choice and male-male competition in shaping the ma...

Fishes represent the stem vertebrate condition and have maintained several gene arrangements common to mammalian genomes throughout the 450 Myr of divergence from a common ancestor. One such syntenic arrangement includes the GPI-PEPD enzyme association on Xiphophorus linkage group IV and human chromosome 19. Previously we assigned the Xiphophorus homologue of the human ERCC2 gene to linkage gro...

Fish of the genus Xiphophorus are polymorphic for black pigmentation patterns. Certain intra- or interspecific hybrids exhibit enhanced expression of these patterns, leading in many cases to malignant melanoma. Because no recombination was ever observed between the pattern information and the genetic predisposition to develop melanoma after hybridization, a "tumor gene" (Tu) was postulated that...

To determine the nutritional requirment for iron in fish growth, the effect of daily addition of supplemental ferrous sulfate on the growth of Xiphophorus helleri and Xiphophorus maculatus (the swordtail and the platyfish) was measured by determination of weight gain and hematocrit levels. Both variables increased as a result of the added iron. The effectiveness of the treatment diminished as s...

Early studies of the thyroid tumors of trout (3—5)have demonstrated the relationship between iodine supply and hyperplastic growth of thyroid cells. Experimental work with fishes provided much of the background for the present under standing of the etiology of human goiters. In con trast with encapsulated mammalian goiters, how ever, hyperplastic thyroids in fishes are remark able for their i...

Several species of the genus Xiphophorus are polymorphic for specific pigment patterns. Some of these give rise to malignant melanoma following the appropriate crossings. For one of these pattern loci from the playfish Xiphophorus maculatus the melanoma-inducing gene has been cloned and found to encode a novel receptor tyrosine kinase, designated Xmrk. Using molecular probes from this gene in S...