In the life of an organism (ontogeny), phenotypic changes happen throughout the time. This contribution is a review of: a) terms and definitions used in studies of the ontogeny, b) the importance to distinguish between shape variation (development) and size variation (growth); and c) the need to consider the real time (age) in which the ontogeny takes place. Based on available information about the ontogeny among tetrapods with emphasis in anurans and nonavian sauropsids, it is outlined the need to increase the information about the ontogeny for comparative studies. We denote the relevancy to get tables of development to identify ontogenetic variation, the study of three fundamental components of ontogenies (it forms - size-time), and the processes that the age organizes (development and growth) to contribute the paradigm of the Evolution of the Development.

En la vida de un organismo (ontogenia) suceden cambios fenotípicos a lo largo del tiempo. Esta contribución es una revisión de: a) términos y definiciones usados en estudios de la ontogenia, b) la importancia de distinguir entre la variación de la forma (desarrollo) y del tamaño (crecimiento); y c) la necesidad de considerar el tiempo real (edad) en el que se organiza la ontogenia. Sobre la base de información disponible de la ontogenia en tetrápodos con énfasis en anuros y saurópsidos no avianos, se destaca la necesidad de incrementar la información sobre la ontogenia para estudios comparados. Enfatizamos en la relevancia y pertinencia de contar con tablas de desarrollo donde se describa la variación en trayectorias ontogenéticas y el estudio de los tres componentes fundamentales de las ontogenias (forma-tamaño-tiempo) y los procesos que la edad organiza (desarrollo y crecimiento) para avanzar en el paradigma de la Evolución del Desarrollo.

The aim of this study was to investigate the genetic diversity within and among three breeds of sheep: Corriedale, Merino and Creole. Sheep from the three breeds (Merino n = 110, Corriedale n = 108 and Creole n = 10) were genotyped using the Illumina Ovine SNP50 beadchip®. Genetic diversity was evaluated by comparing the minor allele frequency (MAF) among breeds. Population structure and genetic differentiation were assessed using STRUCTURE software, principal component analysis (PCA) and fixation index (F ST). Fixed markers (MAF = 0) that were different among breeds were identified as specific breed markers. Using a subset of 18,181 single nucleotide polymorphisms (SNPs), PCA and STUCTURE analysis were able to explain population stratification within breeds. Merino and Corriedale divergent lines showed high levels of polymorphism (89.4% and 86% of polymorphic SNPs, respectively) and moderate genetic differentiation (F ST = 0.08) between them. In contrast, Creole had only 69% polymorphic SNPs and showed greater genetic differentiation from the other two breeds (F ST = 0.17 for both breeds). Hence, a subset of molecular markers present in the OvineSNP50 is informative enough for breed assignment and population structure analysis of commercial and Creole breeds.