question_answer 57)

Write brief note on the following (a) Synaptonemal complex                                          (b) Metaphase plate

Answer:

                (a) Synaptonemal complexes are zipper-structures which are assembled between homologous chromosomes during the prophase of the first meiosis. Their assembly and disassembly correlate with the successive chromatin rearrangements of meiotic prophase namely the condensation, pouring, recombination and dysfunction of homologous chromosomes. They are considered to be the structures that control the number and distribution of reciprocal exchanges between homolgous chromosomes. They also are known to convert cross over into functional chiasmata . (b) In metaphase, the centromeres of the chromosomes assemble themselves on the metaphase plate (equatorial plate), an imaginary line that is equidistant from  two centrosome poles. This even alignment is due to the opposing kinetochore microtubules. At this plate, chromosomers, especially sisterchromatids are attached to the bundle of four to eight spindle fibres.