Chapter 2: Genetics
Fred W. Allendorf and Moira M. Ferguson
Children look like their parents, only different. This is the essence of genetics. How are morphological, behavioral, and physiological characteristics transmitted from generation to generation? The science of genetics began with the experiments of an Austrian monk who studied how seven morphological differences in the garden pea are inherited. The principles described by Gregor Mendel have proven to be universal in plants and animals and still stand as the foundation of modern genetics.
Genetics has been defined as the study of differences among individuals (Sturtevant and Beadle 1939). If all the individuals in a particular species were identical, we could still study their morphology, physiology, ecology, etc. However, geneticists would be out of work. The study of inheritance depends upon finding individual differences so that the similarity of parents and their offspring can be compared relative to the similarity among unrelated individuals.
Genetic variability can be thought of as existing at two levels: (1) genetic differences between individuals within local populations, and (2) genetic differences between local populations within the same species. The first level is investigated by traditional Mendelian genetics. However, the study of how individual variability becomes transformed into differences between populations is fundamental to the study of evolution. In this chapter, we are concerned with the study of both inheritance and evolutionary genetics as they relate to an understanding of the biology of fish populations.
An understanding of the principles of genetics is important for many aspects of fisheries science. Genetics is, of course, fundamental to fish husbandry programs practiced in hatcheries. An understanding of the genetic bases of differences in morphology, physiology, and behavior is also essential to fisheries biology. Genetic analysis of population structure is critical for proper management of mixed-stock fisheries. In addition, the taxonomic classification and systematic investigation of fish species requires knowledge of the amount of genetic divergence among populations and species.