The chapter discusses the genetic distance between populations and its relation to Wahlund's principle, which explains the excess of homozygous carriers in a mixture of reproductively isolated subpopulations. The principle is expressed as a function of genic distances among subpopulations, which can be used to recognize seed lot mixtures. The effect of bulking is distinguishable from inbreeding and assortative mating by analyzing distances at multiple gene loci. Selection effects can complicate the inference of seed lot mixtures, so application should be limited to dormant seeds. Isozyme loci are recommended for such checks due to their low frequency of complete dominance. The chapter also discusses the advantages of conifer seeds in this context. Key concepts include: - **Genetic distance**: A measure of the genetic variation between populations. - **Wahlund's principle**: The excess of homozygotes in a mixture of subpopulations due to reproductive isolation. - **Inbreeding**: The reduction in genetic diversity due to self-fertilization. - **Assortative mating**: Non-random mating that leads to increased genetic similarity within groups. - **Selection**: Environmental pressures that can affect genetic diversity. The chapter provides a detailed mathematical derivation of Wahlund's effect on homozygote surplus and its relation to genetic distances, using a measure of genic distance developed by Gregorius. The formula for the variance in homozygote frequency is derived, and the conditions under which the variance reaches its maximum are discussed. The chapter also outlines methods for inferring the proportion of subpopulations from observed homozygote frequencies.The chapter discusses the genetic distance between populations and its relation to Wahlund's principle, which explains the excess of homozygous carriers in a mixture of reproductively isolated subpopulations. The principle is expressed as a function of genic distances among subpopulations, which can be used to recognize seed lot mixtures. The effect of bulking is distinguishable from inbreeding and assortative mating by analyzing distances at multiple gene loci. Selection effects can complicate the inference of seed lot mixtures, so application should be limited to dormant seeds. Isozyme loci are recommended for such checks due to their low frequency of complete dominance. The chapter also discusses the advantages of conifer seeds in this context. Key concepts include: - **Genetic distance**: A measure of the genetic variation between populations. - **Wahlund's principle**: The excess of homozygotes in a mixture of subpopulations due to reproductive isolation. - **Inbreeding**: The reduction in genetic diversity due to self-fertilization. - **Assortative mating**: Non-random mating that leads to increased genetic similarity within groups. - **Selection**: Environmental pressures that can affect genetic diversity. The chapter provides a detailed mathematical derivation of Wahlund's effect on homozygote surplus and its relation to genetic distances, using a measure of genic distance developed by Gregorius. The formula for the variance in homozygote frequency is derived, and the conditions under which the variance reaches its maximum are discussed. The chapter also outlines methods for inferring the proportion of subpopulations from observed homozygote frequencies.