Answer:
The typical behavior of chromosomes in meiosis is that homologous pairs synapse, recombine, and then separate at anaphase I. At anaphase II, sister chromatids separate. However, studies of small chromosomes in maize derived from a variety of sources typically have failure of sister chromatid cohesion at anaphase I. This failure occurs whether there is pairing of two copies of a minichromosome or not. These characteristics have implications for managing the transmission of the first generation artificial chromosomes in plants. Procedures to address these issues of minichromosomes are discussed.
Normal chromosomes enter into meiosis following DNA replication. The homologous pairs find each other in the process of synapsis. Recombination exchanges parts of the homologs involving two of the four chromatids present. Then in anaphase I, each member of the pair segregates to opposite poles and into the two cells resulting from meiosis I. In contrast to mitosis, the sister chromatids of each homolog remain attached to each other. At meiosis II the sisters now separate to opposite poles. The consequence of this sequence of events is that segregation of genetic markers on the two members of the pairs of homologs enter into different gametes that will eventually be formed after meiosis. However, small chromosomes as observed in maize do not follow these rules. In this review, we describe the information known about these minichromosomes and what they inform us about meiotic processes. Also, the behavior of small chromosomes impacts how engineered minichromosomes will behave and so information about them is important for practical applications as well.
