摘要
Sexual reproduction in diploid organisms requires the production of haploid gametes via the process of meiosis, in which a single round of DNA replication is followed by two consecutive cell divisions （or two nuclear divisions and one cytokinesis）. In the majority of known cases the proper segregation of the parental genome into gametes is accom- panied and facilitated by meiotic crossover formation, which contributes to physical association between homologous chromosomes and results in the generation of new combina- tions of alleles in the progeny. This is necessarily a complex and highly regulated process with multiple steps in a tight sequence, including exit from mitosis, DNA double strand break （DSB） formation, homology search, recombinational repair of DSBs and regulation of cohesion between homolo- gous chromosomes. The process of meiosis is astonishingly effective, even in mammals and flowering plants with extremely large genomes, in which this entails the manipula- tion of approximately twelve metres or even more of the replicated diploid DNA, on the order of 10^10 base pairs, with close to base pair accuracy. In plants, meiosis does not pro- duce gametes directly, but progenitors of haploid multicellular structures called gametophytes, which contain haploid cells that differentiate into gametes.
Sexual reproduction in diploid organisms requires the production of haploid gametes via the process of meiosis, in which a single round of DNA replication is followed by two consecutive cell divisions （or two nuclear divisions and one cytokinesis）. In the majority of known cases the proper segregation of the parental genome into gametes is accom- panied and facilitated by meiotic crossover formation, which contributes to physical association between homologous chromosomes and results in the generation of new combina- tions of alleles in the progeny. This is necessarily a complex and highly regulated process with multiple steps in a tight sequence, including exit from mitosis, DNA double strand break （DSB） formation, homology search, recombinational repair of DSBs and regulation of cohesion between homolo- gous chromosomes. The process of meiosis is astonishingly effective, even in mammals and flowering plants with extremely large genomes, in which this entails the manipula- tion of approximately twelve metres or even more of the replicated diploid DNA, on the order of 10^10 base pairs, with close to base pair accuracy. In plants, meiosis does not pro- duce gametes directly, but progenitors of haploid multicellular structures called gametophytes, which contain haploid cells that differentiate into gametes.
