The aim of this study was to investigate genetic diversity in a nucleus flock of Afshari sheep using measures based on the probability of identity-by-descend of genes (coancestry, ƒ, inbreeding, F, average relatedness, AR, and effective population size, Ne), as well as measures based on probabilities of gene origin (effective number of founders, ƒe, effective number of ancestors, ƒa, effective number of founder genomes, ƒg, and effective number of non-founder genomes, ƒne). The average coancestry (f), inbreeding (F), and relatedness (AR) in the whole population were 1%, 0.5%, and 2%, respectively. The estimated value of the effective population size () was 58. Effective number of founders was estimated to be 62 which was one fourth of the total number of founders, indicating the loss of diversity due to the unequal contribution of founders in such a way that only 62 founders covered 75% of the total genetic diversity. The effective number of ancestors (fa) was 49. Only 18 ancestors were needed to explain 50% of the genetic diversity in the population. The marginal contribution of the most influential ancestor was 6.5%. This was 5.8% and 4.8% for the 2nd and 3rd most influential ancestors. Effective number of founder genomes which covered all of the losses in genetic diversity during segregation was computed to be 41 and the effective number of non-founder genomes was 125. While the level of inbreeding was low, it was concluded that the rate of inbreeding needs to be controlled in the future to avoid further decline in genetic diversity.