The uniformity of genome size within mammals implies that all mammals are essentially endowed with the same genome in that most of the gene loci contained in the genome of one species are included in that of the other species. For instance, all placental mammals studied to this date contain three separate gene loci for lactate dehydrogenase (LDH) subunits in their genomes. A and B subunits are produced in a variety of tissues (Markert, 1964), while C subunits are produced only in the sexually mature testis (Goldberg, 1962). The above situation found in mammals is in sharp contrast to the situation found in teleost fish. Some teleosts with minimum-sized genomes, have only a single gene locus for LDH (Markert and Faulhauber, 1965), while tetraploid teleosts such as trout and salmon have as many as 8 separate gene loci for LDH subunits (Massaro and Markert, 1968). Similarly, all placental mammals appear to be characterized by having one gene locus each for the supernatant form and the mitochondrial form of NAD-dependent malate dehydrogenase as well as NADP-dependent isocitrate dehydrogenase. In the case of teleost fish, on the other hand, tetraploid species have two separate gene loci for the supernatant form of each enzyme (Bailey et al., 1969; Quiroz-Gutierrez and Ohno, 1970; Wolf et al., 1970).
KeywordsLactate Recombination Polypeptide Alkaloid Atropine
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