Paternity determination is a practical application of biological variation. Genetic variation between individuals produces unique patterns of DNA, blood groups, fingerprints, and other heritable traits. These differences can be used to determine whether a particular man is the biological father of a child by comparing the child's genetic markers with those of the alleged father and the mother. Techniques such as DNA profiling (genetic fingerprinting) and blood group analysis exploit the fact that no two unrelated individuals (except identical twins) share the same combination of genetic markers.
Sex determination is governed by sex chromosomes (XX or XY in humans) and is a fixed genetic mechanism, not an application of variation across a population. Population control involves managing population size through birth control, family planning, or policy measures and is not directly an application of biological variation. Survival of the fittest (natural selection) is a mechanism of evolution driven by variation, but it is a natural process rather than a deliberate human application of variation.
Other recognised applications of variation include crime detection (forensic fingerprinting), blood transfusion compatibility, and selective breeding in agriculture.
