The Greek word zygoûn (which translates as “unite”) derived in zygōtós (“united”), which in turn came to our language as zygote or zygote. The cell that results from the fusion of the female gamete with the male gamete in the process of sexual reproduction developed by plants and animals is called a zygote.
From the term that occupies us, other equally important ones have emerged, such as the following:
-Heterozygous, which is used to refer to that cell that is formed from the union of two gametes that have different constitution.
-Homozygous, which is used to refer to a cell that is created from the union of two gametes of the same constitution.
Also called an egg, the zygote arises when the sperm unites with the egg. When their respective nuclei fuse, the nucleus of the zygote emerges, which has two complete sets of chromosomes (one from each gamete). Organelles and cytoplasm, meanwhile, come from the ovule.
Once the zygote is formed, its segmentation occurs, which includes successive mitoses to give rise to blastomeres (embryonic cells), which in turn give rise to the morula and then to the blastula. In the continuity of embryonic development, the blastula becomes a gastrula and then a neurula. In this sequence, the zygote goes from the fallopian tube towards the uterus.
The various phases of segmentation are known as blastulation, gastrulation, and organogenesis. When embryonic development is complete, the zygote is called a fetus.
According to the location and level of vitelo (substances that allow the nutrition of the embryo), zygotes can be classified into centrolecíticos (with an abundance of yolk); telolecitics; mesolecitic or heterolecitic; and oligolecitic or isolecitic (with little yolk).
It is important to bear in mind that it is possible to differentiate two major poles in the zygote: the animal or germinative pole, which houses the nucleus and metabolic activity, and the vegetative pole where the aforementioned yolk accumulates.
It should be stated that it is very common to confuse the terms zygote, embryo and fetus. And it is that they are used on a regular basis to refer to the future baby on the way in a pregnancy. However, it must be clear that they mention it but in the different phases of what its prenatal development would be:
-Zygote is the cell that arises when the sperm and the ovum fuse their nuclei during fertilization. It usually has 46 chromosomes and its size is identical to that of the mentioned ovum.
-Embryo is the one that occurs from the first day after fertilization until the eighth week of gestation.
-Fetus. In this case, we can state that it is considered that the end of the embryonic stage and the beginning of the fetal stage take place from week 8 of pregnancy. At this time the embryo is considered to be a fetus. This will make it grow as its vital organs develop and it will acquire the appearance of a baby until it is born, which usually happens between 38 and 40 weeks of pregnancy, as a general rule.