Most immunization refers to group immunity, which refers to the resistance of people or livestock groups to infection. The high level of group immunity means that the percentage of animals in the group who are resistant to infection is high. Because the possibility of disease prevalence depends not only on the number of resistant individuals in the animal population, but also on the frequency of contact between individuals in the animal population.
The frequency and composition of different types of individuals in a biological population (a group composed of several individuals). There are two meanings:
1. Population genetics refers to the genetic composition of a population, that is, the frequency of genes and genotypes in the population. For example, the population of pure line varieties is homogeneous, and the individuals are homozygous; However, the population of open pollination population varieties is heterogeneous, and the individuals are heterozygous. The study of population genetic composition in crop breeding is helpful to the decision of breeding program.
2. In crop cultivation, the individual group composition of crops grown on the same field is limited. This individual group may be composed of several crops mixed planting, intercropping or single planting. Studying the space occupied by each individual in the individual group, the composition of their phenotypes, and the dynamic coordination between individuals will help guide crop high-yield cultivation.