Négysejt

Négysejt is a Hungarian term that translates to "four-cell" in English. It most commonly refers to a stage in the early embryonic development of many animals, including humans. Following fertilization, the zygote undergoes a series of rapid cell divisions known as cleavage. The four-cell stage represents the point where the single-celled zygote has divided into four distinct cells, often referred to as blastomeres.

This stage is a crucial milestone in embryogenesis. The blastomeres at the four-cell stage are still totipotent, meaning each individual cell has the potential to develop into a complete, independent organism. This property is the basis for the natural occurrence of identical twins, which arise from the separation of blastomeres at very early stages of development.

The precise timing and appearance of the four-cell stage can vary depending on the species. However, it generally occurs within the first few days after fertilization. The cells are typically held together by a glycoprotein coat called the zona pellucida. Beyond the four-cell stage, further divisions lead to a morula, a solid ball of cells, which then develops into a blastocyst, a hollow ball of cells that implants in the uterine wall. The concept of the four-cell stage is fundamental in understanding developmental biology and reproductive technologies.