Abstract
Growth is one of the most important aspects in the genetic improvement of cultured fish species. Consequently, genetic parameters related to this feature and their response to selection have been the focus of most research in this area. Such research indicates that, in general, there is enough additive genetic variance related to growth, justifying the use of selection. Based on the usefulness of cytogenetic and molecular markers in the fish culture, the aim of the present work was to analyze the possible relationships among cytogenetic characteristics, specifically the NOR phenotypes, and the increase in length and weight in specimens of the rainbow trout (Oncorhynchus mykiss), resultant from directed mating between homozygous females and heterozygous males according to their NOR phenotypic patterns. The equations of the relationship between length and weight of the analyzed specimens followed the model Wt = a Lt(b), showing b values higher than 3, determinant of a positive allometric growth. The results showed that the different NOR phenotypes were not related with the growth values for length and weight in any statistical test.
Highlights
The nucleolar organizer regions (NORs) are the chromosome segments where the 18S, 5.8S and 28S ribosomal genes are found
An important aspect observed in the studies of NORs in fishes is that the number and location of NORs can be species specific or even population spe
The lack of individuals bearing the homozygous N2N2 NOR phenotype was confirmed, as previously described by Oliveira et al (1996) and in the offspring obtained in N1N2XN1N2 crosses (PortoForesti et al, 2004)
Summary
The nucleolar organizer regions (NORs) are the chromosome segments where the 18S, 5.8S and 28S ribosomal genes are found. The transcription of these genes has been detected by staining the chromosomes with silver nitrate (Miller et al, 1976; Howell and Black, 1980). The silver nitrate staining reveals only active. NORs, since it stains a set of acidic proteins related to the process of ribosomal production and not the ribosomal DNA (Miller et al, 1976). An important aspect observed in the studies of NORs in fishes is that the number and location of NORs can be species specific or even population spe-.
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