Generally speaking, as long as the mathematical probability and statistical knowledge in senior high school have been tested, they can basically be calculated. The only knowledge that needs to be supplemented is chi-square test and three-point test.

Three-point test cross is the test cross between three heterozygotes abc/+++ and three recessive homozygotes abc/abc, where+indicates that the wild type is dominant relative to the recessive mutant gene, which is equivalent to three two-point test cross between A and B, B and C, and A and C. According to the phenotype, the recombination values of ab, ac and bc are obtained respectively, and the graph distance is obtained. Or according to the difference of recombination amount between parental type and double cross type, it is easy to find the intermediate gene among the three genes.