一对染色体

If both of a pair of homologous chromosomes are missing, nullisomy results.

如果一对色体都缺失了，称为缺体。

At this point esch chromosome consist of a pair of chromatids and the two associated chromosomes are termed a tetrad.

此时每条色体由一对色单体构成，这条联合的色体称为四分体。