染色体非整倍性变异的一种.在二倍染色体基础上，某对染色体多了两条，以２ｎ＋２表示.减数分裂偶线期出现四价体，若分析的等位基因恰好处在额外染色体上时，产生的配子类型以及测交、自交后代表现与同源四倍体相同.GOOGLE英文翻译:Chromosome aneuploidy as a variation. Based on the chromosomes in the two-fold, a more two pairs of chromosomes to 2n 2, said. Meiotic zygotene there quadrivalent, if the analysis of additional alleles at just chromosome when the gametes produced by the type of test cross, self-performance and future generations to pay the same autotetraploid.