(a) Synaptonemal complexes are zipper-structures which are assembled between homologous chromosomes during the prophase of the first meiosis. Their asssembly 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 sister chromatids are attached to the bundle of four to eight spindle fibres.

Multicellular organisms grow and develop with the involvement of mitotic cell division. Meiosis occurs in them to form gametes in their reproductive phase of life cycle.

Significance of Mitosis

(i) Multicellular plants and animals start life as single cells. The process of mitosis gives rise to many cells which differentiate to form tissues, organs and organ-systems of the organism.

(ii) It results in increase in size and growth of an organ.

(iii) Cell reproduction is used to form new cells to renew certain tissues and to replace worn out cells.

(iv) Mitosis is also involved in asexual reproduction in some organisms like in unicellular. Amoeba and multicellular Hydra as well as in vegetative reproduction in plants.

Significance of Meiosis

(i) Meiosis is the mechanism by which conservation of specific chromosome number of each species is achieved across generations in sexually reproducing organisms.

(ii) Meiosis also increases the genetic variability in the population of organisms from one generation to the next. Variations are very important for the process of evolution.