1. New technology is developed that provides more information about the theory.
2. New experimental methods are designed to test a theory.
3. A single experiment produces results that differ from all previous experiments.
im not sure about #3 but it could be it
Answer: mitosis.
During DNA replication a pair of chromosomes of from one cell genders two duplicated chromosomes (so the number of chromosomes is duplicated), then in the mitosis process the cell split into two identical cells each with half of the duplicated chromosomes, so at the end one cell with two chromosomes form two cells each with two chromosomes. So, the new generation of cells has the same number of chromosomes.
A scientific law is a statement that summarizes a pattern found in nature.
Hope this helps.