GENOME MAPPING of aquaculture species

Linda Benedict, Tiersch, Terrence R., Cooper, Richard K.  |  5/22/2009 7:52:50 PM

Geneticists develop maps of DNA molecules to aid in understanding inheritance patterns. One kind of map, called agenetic linkage map, describes inheritance of observable traits, such as color or shape, and usually involves breeding studies to compare parents and offspring. Physical genome maps describe the actual geography of chromosomes, the DNA-bearing structures within the control center (nucleus) of a cell. These maps do not require breeding studies. Physical maps are derived mainly from chemical measurements made on the DNA molecules of an organism, referred to collectively as the “genome.”  These maps can identify the genes that carry the blueprints for the proteins necessary for life or stretches of genetic material with no known function. In the Human Genome Project, amassivere search effort to characterize the complete DNA sequence of  human beings,both of these map types are considered equally important and are being developed in parallel.

Genetic linkage studies of economically important fishes, such as salmon and trout, are fairly well established and have been started recently for channel catfish. But little work has been done in aquatic species to address physical genome mapping. Until recently, all that was known about channel catfish was that they have 29 pairs of chromosomes. The fact that humans have 23 pairs has been known for decades. Despite the economic importance of channel catfish, little information exists about genetic markers for production traits such as improved growth and disease resistance. This is the situation for all of the aquaculture species of Louisiana.

A chromosome map provides landmarks for gene location. Techniques are well developed for mammalian chromosomes to produce multiple high-resolution markers called bands. These techniques have yielded little success when applied to fish species, however. Fish chromosomes are more difficult to study than human chromosomes for several reasons including their large numbers (sometimes more than 100), small size (a third of the size of human chromosomes ) and uniformity. There are many of them, and they all look a like. A long - term team goal is to prepare detailed chromosome maps (called banded karyotypes ) for the cultured fish and shellfish of Louisiana. Based on this information, we will identify the locations of genes of economic importance, such as for disease resistance and growth rate, and develop DNA markers to use in genetic improvement including hybridization, selective breeding and gene transfer studies.

Because of genetic similarity among organisms, physical  mapping of catfish or oyster genes can be performed with information obtained from mammalian species, including humans. This offers significant benefits from comparative studies and demonstrates a direct application of well - funded human medical research to the study of aquaculture species, which receives much less funding and effort. We have developed techniques to identify the location of individual genes on chromosomes of fish and shellfish. Our laboratory was the first to map genes of catfish and oyster (or any aquatic species) by a technique known as in situ polymerase chain reaction. This technique identifies the gene location by making copies of the DNA,  which can be labeled and identified using a microscope.

Acknowledgments

Personnel involved in genome mapping research include John Buchanan, Philip Cheng, BrandyeSmithandGangYu. 

Terrence R. Tiersch, Professor, Aquaculture Research Station; Quiyang Zhang, Postdoctoral Scientist, and Richard K. Cooper, Associate Professor, both in the Department of Veterinary Microbiology and Parasitology, LSU Agricultural Center, Baton Rouge, La.

(This article was published in the fall 1999 issue of Louisiana Agriculture.)

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