Leptonema

Leptonema (from the Greek words “lepto” - thin and “nema” - thread) is the first stage of prophase I of meiosis. It is characterized by chromosome condensation and an active search for homologous chromosomes for subsequent pairing.

During leptonema, chromosomes shorten and thicken, taking on the appearance of thin threads. There is an active synthesis of proteins necessary for the subsequent exchange of sections between homologous chromosomes. Homologous chromosomes begin to “recognize” each other with the help of special proteins and come together in pairs for further synapsis.

Thus, leptonema is a preparatory stage of meiosis, when a morphological rearrangement of chromosomes occurs and a search for homologs occurs for subsequent genetic exchange between them during crossing over. This is necessary to increase the genetic diversity of germ cells.