What leads to population in variation

Genetic variation can be caused by mutation (which can create entirely new alleles in a population),random mating,random fertilization,and recombination between homdogous charosomes alleles within an organism's offspring).

every chemical equation adheres to the law of conservation of mass, which states that matter cannot be created or destroyed. therefore, there must be the same number of atoms of each element on each side of a chemical equation.