Which cell communication happens within a cell?

There are a few different types of cell-cell interactions. Some of these interactions are meant for big molecules that enter and exit the cell called, endocytosis (entering the cell) and exocytosis (exiting the cell). For smaller particles like amino acids, water, ions and other solutes there are different types of direct contact between the cells called gap junctions.

a tetrad is the foursome during meiosis made by two homologous chromosomes that have each already replicated into a pair of sister chromatids.