cigoto

Cigoto, in biology, is the initial cell formed when a sperm fertilizes an egg. It is a diploid cell containing a complete set of chromosomes from both parents. The term derives from Greek and is used in Spanish as well as other languages to denote this early embryonic stage.

After fertilization, the cigoto undergoes rapid mitotic divisions without growing in size, a process called cleavage. This sequence transforms a single cell into a multicellular embryo. In humans, the first divisions occur roughly 24 to 36 hours after fertilization, producing 2- to 4-cell stages. By about day 4, a morula forms, and by days 5–6 a blastocyst develops, which then implants into the uterine lining.

The cigoto is totipotent, meaning its cells have the potential to differentiate into all embryonic and extraembryonic tissues. During early development, the genome becomes transcriptionally active, and maternal gene products are gradually degraded as the embryo begins to use its own genetic instructions.

In clinical and reproductive contexts, the cigoto represents a critical stage in assisted reproduction, IVF procedures, and preimplantation genetic testing. Its successful formation marks the transition from gametes to a developing embryo, setting the foundation for subsequent development of the fetus and supporting structures.