Relationship between pachytene synapsis, metaphase I associations, and transmission of 2B and 4B chromosomes in rye.
2B rye plants selected for high (H) or low (L) B transmission rate were studied at pachytene and metaphase I of meiosis to determine the relationship between synapsis, bivalents at metaphase I, and B transmission rate. The results show that the 2 B chromosomes (Bs) form bivalents at pachytene in both the H and L lines, whereas the frequency of bivalents at metaphase I is much higher in the H than in the L line. This demonstrates that B transmission is mainly related to the proper association of Bs at metaphase I, as well as that synapsis of the 2 Bs in the L line is normal, but the bivalent is not consolidated by a chiasma in most cases. Crosses were made between 2B plants of the H and L lines in all combinations (H x H, H x L, L x H, and L x L) to obtain 4B plants. Similarly, bivalent formation at pachytene and metaphase I was studied. The results show that 4B plants of the H x H and L x L classes differ significantly at pachytene and metaphase I since the former forms more bivalents. The heterozygous 4 Bs of the H x L and L x H classes show intermediate values. The relation H x H > H x L > L x H > L x L was consistently found for the variables transmission rate, bivalents at pachytene, bivalents at metaphase I, and B mean chiasma frequency. A maternal effect was also found. Our data suggest that there are two separate mechanisms acting upon synapsis and chiasma formation in H and L B chromosomes: (i) there is variable efficiency of the control of synapsis at early stages of meiosis; and (ii) there is variable efficiency of the control of the number of chiasmata.
Jiménez
G
G
Departamento de Genética, Facultad de Biología, Universidad Complutense, Madrid, Spain.
Manzanero
S
S
Puertas
M J
MJ
D016009:Chi-Square Distribution; D003433:Crosses, Genetic; D017343:Genes, Plant; D008540:Meiosis; D008677:Metaphase; D009630:Nondisjunction, Genetic; D010641:Phenotype; D012434:Secale / Q000235:genetics*