Structure and genetic variability of the Mexican Sardo Negro breed

ABSTRACT: This study analyzed the Sardo Negro breed pedigree (41,521 animals registered from 1958 to 2019) to determine its structure, evolution, and genetic variability (GV). The population genetic parameters evaluated were effective number of founders (fe) and ancestors (fa), pedigree integrity, additive genetic relationship (AGR); number of complete generations (NCG), maximum generations traced (NMGT), and equivalent complete generations (NECG); effective population size (Ne), inbreeding coefficient (F), and generation interval (GI). The average GI was 7.45 years. A total of 7,804 founders and 4,856 ancestors were identified for a fe of 185 and a fa of 97. The average and maximum values of NCG, NECG, and NMGT were 1.6 and 5.0, 2.5 and 6.5, 4.3 and 12, with Ne estimates of 15.9, 25.9, and 69.0, respectively. The increase in F, linked to Ne, ranged from 0.72% to 3.1% per generation. The average values for F and AGR were 3.6% and 1.0%, respectively. The proportion of inbred individuals was 32.0%, with F values ranging from 0.01 to 62.2% and an average of 11.3%. The rate of inbred population was 1.3% per year. The annual rate of AGR was 0.04%. For the continuity and projection of the breed, the evolution of F as a function of Ne and the possible implications of the selection schemes must be considered. The genetic variability sustained over time results from the Ne.

A note on genetic parameters and accuracy of estimated breeding values in honey bees

Background In honey bees, observations are usually made on colonies. The phenotype of a colony is affected by the average breeding value for the worker effect of the thousands of workers in the colony (the worker group) and by the breeding value for the queen effect of the queen of the colony. Because the worker group consists of multiple individuals, interpretation of the variance components and heritabilities of phenotypes observed on the colony and of the accuracy of selection is not straightforward. The additive genetic variance among worker groups depends on the additive genetic relationship between the drone-producing queens (DPQ) that produce the drones that mate with the queen. Results Here, we clarify how the relatedness between DPQ affects phenotypic variance, heritability and accuracy of the estimated breeding values of replacement queens. Second, we use simulation to investigate the effect of assumptions about the relatedness between DPQ in the base population on estimates of genetic parameters. Relatedness between DPQ in the base generation may differ considerably between populations because of their history. Conclusions Our results show that estimates of (co)variance components and derived genetic parameters were seriously biased (25% too high or too low) when assumptions on the relationship between DPQ in the statistical analysis did not agree with reality.

Genetic contributions of Finnish Ayrshire bulls over four generations

The long-term genetic contributions were calculated for 219 Finnish Ayrshire bulls born between 1958 and 1964 to 707 Finnish Ayrshire bulls made available for artificial insemination and born between 1986 and 1988. Three strategies were employed:(i) using all known pedigree information; (ii) ignoring information on the dam of females; (iii) only using information on sires. Expected contributions were calculated using gene flow matrices.The contributions from strategies 1, 2 and 3 were only 0.6 (1 and 2) or 0.7 (strategy 3) of those expected. The causes of this shortfall for strategies 2 and 3 were identified as (i) the use of an imported sire and (ii) generation skipping. For strategy 1, 0.2 of the expected pathways remained unaccounted for and were ascribed to missing pedigree information.Of the 219 ancestors, only 86 made positive contributions to the descendants. Only 10 ancestors made contributions more than the average, and one bull accounted for 0.3 of all pathways traced on strategy 2. There was general agreement in the relative contributions of individual bulls when assessed using the three strategies.The rate of inbreeding (ΔF) estimated by regression from 1974 to 1988 and using known pedigrees was 0.0018 per year and the average coefficients of additive genetic relationship among cohorts was increasing by 0.0030 per year. AF was estimated using the contributions calculated by strategies 1, 2 and 3 to be 0.0147, 0.0151 and 0.0125 per generation respectively. These were converted into rates per year by assuming a generation interval of 6.5 years taken from both published and new information on generation intervals in the Finnish Ayrshire population. This gave annual rates of 0.0023, 0.0023 and 0.0019. The estimates from strategy 3 were obtained without the use of any pedigree information pertaining to dams.

Inheritance of seed quality traits and concentrations of zinc and iron in maize topcross hybrids

Information about the mode of inheritance of maize (Zea mays L.) seed quality traits is crucial in planning for improvement programmes for such traits. The objective study was to determine mode of inheritance and interrelationships between seed quality traits, and Fe and Zn contents in maize. Twenty-six maize genotypes were considered for evaluation in this study. Additive gene action was prevalent for most seed quality traits (>50%); while non-additive gene action was preponderant for Fe and Zn concentrations. Inbreds TZEEI82 and TZEEI64 were outstanding in terms of GCA male effects for conductivity (-0.13** and -0.06*), root number (0.79** and 0.30*), and root fresh weight (0.90*). Genotypes TZEEI81, DTE-STR-Y-SYN-POP-C3, 2009-TZEEI-OR1-STR and 2009-TZEE-OR1-STR-QPM were identified as excellent pollen parents for Fe concentration; and TZEEI58 and TZEEI64 for Zn concentration. In addition, only germination index had a significant additive genetic relationship with Fe content (r=0.57*); while both shoot fresh and dry weights had significant positive correlations with Zn content (r=0.45*, 0.53*). Overall, it is clear that different modes of gene action control inheritance of seed quality traits and Fe and Zn concentrations.