From the testcross performance data, selections, based on an index, were made for intermating of each of the four groups. 根据测交种数据，利用指数方法进行选择，方法是对每个杂种优势群进行相互交配。
a cross between an organism whose genotype for a certain trait is unknown and an organism that is homozygous recessive for that trait so the unknown genotype can be determined from that of the offspring
