A molecular cytogenetic analysis of chromosome behavior in Lilium ...

Chapter 3abnormal bivalents, in all other cases variable frequencies of bivalents and univalents wereobserved. Because of chromosome pairing abnormalities, the expected metaphase Iorientation at the equatorial plate of the cell was rare.Anaphase I separationSince anaphase I separation of homoeologous chromosomes occurred regularly only in someof the pollen mother cells, normal metaphase I orientation had occurred in those cases. Inother cases, the chromosomes (half-bivalents) were present haphazardly in the cells (Fig. 3.2a,b, c and d). Nevertheless, it was possible to identify the pairs of half-bivalents with andwithout recombinant segments in the sister and non-sister chromatids. The remarkable featurewas that it was possible to identify the types of crossovers that had occurred between the nonsisterchromatids of the pairs of homoeologous chromosomes during meiosis based ondifferential fluorescence. Based on the number and positions of recombinant segments on thenon-sister chromatids it was possible to classify the types of intergenomic recombinationevents that had occurred. These were classified into five classes: a) two strand single (Fig.3.2a and c), b) two strand double (Fig. 3.2b and c), c) three strand double (Fig. 3.2a and d), d)four strand double (Fig. 3.2a, b and d) and e) multiple cross-overs (Fig. 3.2d). The frequenciesof each of these events were estimated in five genotypes (Table 3.2). From an analysis of atotal of 637 pairs of half-bivalents it was evident that a large majority (65 %) were two strandsingle crossing overs, 5.5 % were two strand double, 3.0 % three strand double, 9.3 % fourstrand double and 17.3 % were multiple crossing over events. Although there was differencesin the frequencies of these events, two conclusions could be made from these observations. 1)Regardless of the type of cross-over event, equational separation had occurred for therecombinant segments. 2) All the five crossover types of half-bivalents were similar to theevents that are expected (Fig. 3.2) following a normal meiosis in the parent. This evidentlyindicated that despite genome differentiation between the genomes of the species of L.longiflorum and Asiatic lilies they retained homoeology that enabled normal crossing-overbetween the homoeologous pairs of chromosomes. In the two genotypes (006001-6 and006001-13) with multivalent and nonhomologous bivalent formation there was no deviation atanaphase I that could be observed with regard to disjunction as compared with othergenotypes without multivalent formation.38