Meiosis is an event of high evolutionary stability which culminates in a reduction of chromosome number. The normal and harmonious course of meiosis ensures gamete viability. The cytologic events of gametogenesis are controlled by a large number of genes that act from premeiotic to postmeiotic mitosis. Mutations in these genes cause anomalies that may impair fertility, and many abnormalities affecting plant fertility or causing total male sterility have been detected during the evaluation of meiotic behavior in some species. Some of these abnormalities have been frequently described in the literature, while others have not been previously reported. The most frequent abnormalities found in the species analyzed were irregular chromosome segregation, cytomixis, chromosome stickiness, mixoploidy, chromosome fragmentation, syncyte formation, abnormal spindles, and failure of cytokinesis. Uncommon abnormalities, such as chromosome elimination during microsporogenesis, were found in one species. Original meiotic mutations affecting different steps of meiosis were also observed in these species, especially in maize, Paspalum and soybean. Some mutants present characteristics that may be exploited successfully in breeding programs because they cause total male sterility.
A meiose é um evento de alta estabilidade evolucionária que culmina na redução do número de cromossomos. O curso normal e harmonioso da meiose garante a viabilidade gamética. Os eventos citológicos da gametogênese são controlados por um grande número de genes que atuam desde as mitoses pré-meióticas até as pós-meióticas. Mutações nestes genes causam anomalias que podem afetar a fertilidade. Durante a avaliação do comportamento meiótico em algumas espécies de plantas, muitas anormalidades que afetaram a fertilidade ou causaram total macho-esterilidade foram detectadas. Algumas das anormalidades encontradas já eram descritas na literatura, enquanto outras eram totalmente desconhecidas. As anormalidades mais freqüentes nas espécies analisadas foram segregação irregular de cromossomos, citomixia, aderências cromossômicas, mixoploidia, fragmentação cromossômica, formação de sincícios, fusos anormais e falta de citocinese. Eliminação de cromossomos, uma anormalidade meiótica rara, foi observada em uma espécie de Paspalum. Mutantes meióticos nunca antes descritos, afetando diferentes passos da meiose, foram observados em algumas espécies, especialmente em milho, soja e Paspalum. Alguns mutantes apresentam características que podem ser exploradas com sucesso em programas de melhoramento, pois causam total macho-esterilidade

Brachiaria humidicola (Rendle) Schweick. is a warm-season grass commonly used as forage in the tropics. Accessions of this species were collected in eastern Africa and massively introduced into South America in the 1980s. Several of these accessions form a germplasm collection at the Brazilian Agricultural Research Corporation. However, apomixis, ploidy, and limited knowledge of the genetic basis of this germplasm collection have constrained breeding activities. The objectives of this work were to identify genetic variability in the Brazilian B. humidicola germplasm collection using microsatellite markers and to compare the results with information on the following: (1) collection sites of the accessions; (2) reproductive mode and ploidy levels; and (3) genetic diversity revealed by morphological traits. The evaluated germplasm population is highly structured into four major groups. The sole sexual accession did not group with any of the clusters. Genetic dissimilarities did not correlate with either geographic distances or genetic distances inferred from morphological descriptors. Additionally, the genetic structure identified in this collection did not correspond to differences in ploidy level. Alleles exclusive to either sexual or apomictic accessions were identified, suggesting that further evaluation of the association of these loci with apospory should be carried out.

Considering that the production of grains is a characteristic closely related to meiotic behavior, the purpose of the present study was to evaluate some oat cultivars recommended for the southern region of Brazil in order to verify if those which currently do not display a good performance present meiotic irregularities that might be impairing the production of viable gametes. The most common meiotic abnormalities were those related to the irregular segregation of chromosomes, characterized by the presence of precocious chromosome migration to the poles or laggard chromosomes and of non-oriented bivalents at the equatorial plate. In general, these chromosomes gave rise to micronuclei during telophase that remained until the tetrad stage. Another very common meiotic abnormality in all varieties was the occurrence of multiple bridges in anaphase I and II. Other less common meiotic abnormalities, such as cytomixis, mixoploidy and chromosome stickiness were observed in some varieties. Although meiotic abnormalities can cause pollen sterility, there was no correlation between these abnormalities and sterility. The percentage of sterile pollen grains was much lower than expected. The grains produced by the 12 cultivars ranged from 820 to 2601 kg/ha, showing no correlation with the rate of meiotic abnormalities or pollen fertility. Thus, the results obtained by cytological analysis suggest that the meiotic abnormalities were not the sole factors responsible for the decrease of productivity in the varieties analyzed.