Division of Biological Sciences, University of Missouri, Columbia, MO 65211, USA.
Open Biol. 2021 Nov;11(11):210197. doi: 10.1098/rsob.210197. Epub 2021 Nov 3.
The supernumerary B chromosome of maize is dispensable, containing no vital genes, and thus is variable in number and presence in lines of maize. In order to be maintained in populations, it has a drive mechanism consisting of nondisjunction at the pollen mitosis that produces the two sperm cells, and then the sperm with the two B chromosomes has a preference for fertilizing the egg as opposed to the central cell in the process of double fertilization. The sequence of the B chromosome coupled with B chromosomal aberrations has localized features involved with nondisjunction and preferential fertilization, which are present at the centromeric region. The predicted genes from the sequence have paralogues dispersed across all A chromosomes and have widely different divergence times suggesting that they have transposed to the B chromosome over evolutionary time followed by degradation or have been co-opted for the selfish functions of the supernumerary chromosome.
玉米的额外 B 染色体是可有可无的，它不包含任何重要基因，因此在玉米品系中其数量和存在是可变的。为了在种群中得以维持，它具有一种驱动机制，包括花粉有丝分裂时的不分离，从而产生两个精子细胞，然后带有两个 B 染色体的精子在双受精过程中优先与卵子受精，而不是中央细胞受精。B 染色体的序列与 B 染色体的异常一起具有与不分离和优先受精相关的局部特征，这些特征存在于着丝粒区域。序列预测的基因与分散在所有 A 染色体上的基因具有平行关系，它们的分化时间差异很大，这表明它们在进化过程中已经转座到 B 染色体上，随后发生了降解，或者被超数染色体的自私功能所利用。
