ABSTRACT
Theoretically, any genomic DNA sequence can be used in a search for polymorphisms associated with the phenotype of interest. Practical considerations suggest, however, the use of probes derived from genes which, through independent lines of evidence, may be associated with a desired genetic trait. The growth hormone/prolactin gene family is of particular interest in the study of production traits in domestic species. The pituitary hormones of this gene family, growth hormone (GH) and prolactin (PRL), are involved in a variety of processes with economic impact for many domestic animals. The prolactin and growth hormone genes have been the subject of intensive study for some time, and much is known about their structure, regulation, products, and actions across species. Like the growth of the fetus, the mass of the placenta itself increases exponentially early in gestation, and its size and function determine fetal access to maternal gas exchange and nutrients.
