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
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。
