在遗传的基本规律中,子二代的表现型通常具有一定的比例。如在基因分离定律中,子二代中显性与隐性的比例为3:1,测交后代的显性与隐性的比例为1:1。在基因自由组合定律中,子二代的各种表现型的比例为9:3:3:1,测交后代的各种表现型的比例为1:1:1:1。根据这些有规律的比例,就能很快地判断出杂交亲本是一对相对性状的基因分离, In the basic laws of inheritance, the phenotypes of the second generation usually have a certain proportion. For example, in the law of gene segregation, the ratio of dominant to recessive in the second generation is 3:1, and the ratio of dominant and recessive offspring in the test cross is 1:1. In the law of free combination of genes, the ratio of various phenotypes of the second generation is 9:3:3:1, and the ratio of various phenotypes of the test generation is 1:1:1:1. According to these regular proportions, it can be quickly determined that the cross parent is a pair of relative traits for gene isolation.