Population structure of Brazilian Gyr dairy cattle

The objective of the present study was to evaluate the genetic structure of Gyr cattle selected for milk production. Files of pedigree and production were composed of 27,610 animals. The ENDOG program was used for the calculation of individual inbreeding coefficient (F) and coefficient of average relatedness (AR), effective number of animals(Ne), effective number of founders (f e) and ancestors (f a), and generation interval (GI). Individual inbreeding coefficients and average relatedness in the population were 2.82% and 2.10%, respectively. It was observed a reduction in the effective number of animals, especially after publication of the results of the first progeny test. The estimated effective number of founders was 146 and 75 for the ancestrals. Out of those, only 28 ancestors accounted for the origin of 50% of the population genes. The average generation interval was 8.41 years and it was longer for males than for females. For maintaining genetic variability in future generations, it should be invested mating strategies that reduce inbreeding and which do not use massively only some high breeding value sires.O objetivo neste trabalho foi avaliar a estrutura genética da raça Gir selecionada para produção de leite. Os arquivos de pedigree e de produção eram compostos de 27.610 animais. Utilizou-se o programa ENDOG para cálculo dos coeficientes individuais de endogamia (F) e coeficiente de relação médio (AR), número efetivo de animais (Ne), de fundadores (fe) e de ancestrais (fa) e do intervalo de gerações (GI). Os coeficientes individuais de endogamia e de relação médios da população foram 2,82 e 2,10%, respectivamente. Foi observada redução do número efetivo de animais, especialmente após a publicação dos resultados do primeiro teste de progênie. O número efetivo de fundadores estimado foi de 146 e o de ancestrais, 75. Desses, apenas 28 ancestrais foram responsáveis pela origem de 50% dos genes da população. O intervalo médio de gerações foi 8,41 anos e foi maior para machos que para fêmeas. Para manutenção da variabilidade genética em futuras gerações, deve-se investir em estratégias de acasalamento que reduzam a endogamia e que não façam uso maciço de apenas alguns reprodutores de alto valor genético

Gaia Early Data Release 3: The celestial reference frame (Gaia-CRF3)

Context. Gaia-CRF3 is the celestial reference frame for positions and proper motions in the third release of data from the Gaia mission, Gaia DR3 (and for the early third release, Gaia EDR3, which contains identical astrometric results). The reference frame is defined by the positions and proper motions at epoch 2016.0 for a specific set of extragalactic sources in the (E)DR3 catalogue. Aims. We describe the construction of Gaia-CRF3 and its properties in terms of the distributions in magnitude, colour, and astrometric quality. Methods. Compact extragalactic sources in Gaia DR3 were identified by positional cross-matching with 17 external catalogues of quasi-stellar objects (QSO) and active galactic nuclei (AGN), followed by astrometric filtering designed to remove stellar contaminants. Selecting a clean sample was favoured over including a higher number of extragalactic sources. For the final sample, the random and systematic errors in the proper motions are analysed, as well as the radio-optical offsets in position for sources in the third realisation of the International Celestial Reference Frame (ICRF3). Results. Gaia-CRF3 comprises about 1.6 million QSO-like sources, of which 1.2 million have five-parameter astrometric solutions in Gaia DR3 and 0.4 million have six-parameter solutions. The sources span the magnitude range G = 13-21 with a peak density at 20.6 mag, at which the typical positional uncertainty is about 1 mas. The proper motions show systematic errors on the level of 12 μas yr-1 on angular scales greater than 15 deg. For the 3142 optical counterparts of ICRF3 sources in the S/X frequency bands, the median offset from the radio positions is about 0.5 mas, but it exceeds 4 mas in either coordinate for 127 sources. We outline the future of Gaia-CRF in the next Gaia data releases. Appendices give further details on the external catalogues used, how to extract information about the Gaia-CRF3 sources, potential (Galactic) confusion sources, and the estimation of the spin and orientation of an astrometric solution