Synaptonemal Complex

Montrose J. Moses (1956) firstly described synaptonemal complex (SC) in primary spermatocytes of crayfish and D. Fawcett in spermatocytes of pigeon, cat and man.

What is Synaptonemal Complex? – Definition

The synaptonemal complex is a tripartite, protein structure. It forms between two homologous chromosomes during meiotic division in all animal and plant nuclei.

Structure of Synaptonemal Complex

It consists of two parallel lateral regions and a central element. All are electron dense elements that are separated by less electron dense areas.

Central element: Has ladder like configuration. Contains mainly RNA and proteins and has little DNA. It is spanned between the two lateral elements.

Lateral element: Composed of transverse filaments, called as synaptomers. These are rich in DNA, RNA and proteins.

Meiotic stages and Synaptonemal Complex

Leptotene: The lateral elements begin to be formed.

Zygotene: The lateral elements initiate and complete their pairing

Pachytene: Tripartite structure is seen during the pachytene stage of the first meiotic prophase.

After the end of pachytene: The SC usually becomes disassembled and can no longer be identified.

Functions of Synaptonemal Complex

  • Synaptonemal complex stabilizes the pairing of homologous chromosomes i.e. synapsis.
  • It facilitates crossing over.
  • Synaptonemal complex appears during the meiotic stages in which pairing and recombination occurs. So it may be useful to probe the presence of pairing abnormalities in individuals carrying chromosomal abnormalities, either in chromosome number or structure.