This stage is crucial because the dividing cells are more sensitive to the effects of mutagens. From one-celled, it will soon become multicellular, as each cell will undergo mitosis. ![]() In the above picture, the period of ‘ zygote to embryo’ is marked by rapid and extensive mitosis. (Ref.2) Furthermore, the cells are expected to contain the same genetic composition since they divide mitotically. chorion and amnion).īecause the cells divide fast, with no time to grow, the morula tends to have the same size as the zygote. Thus, the zygote not only forms the embryo but will also be the source of the subsequent outer fetal membranes (i.e. The trophoblast, in turn, will give rise to cells that will become the structures essential during the uterine wall implantation and the developmental growth of the embryo to the fetus in the uterus. The inner cell mass will differentiate into cells that will later define an embryo. the outer trophoblast layer and the inner cell mass) and a cavity called the blastocoel. This mass of cells is not going to be a full solid sphere but a sphere with distinct layers (i.e. As they continue to divide, they eventually form a solid mass of cells, called a morula. When does a zygote become an embryo? In humans, at week one post-fertilization, the cells undergo extensive and rapid growth. In humans, the embryo stage is the first eight weeks post-fertilization.Īn embryo is a living form consisting of many cells as a result of a zygote that underwent a series of mitosis and will soon develop a set of tubes. (Ref.1) The next is the embryo stage, which is highlighted by the formation of the embryo (embryogenesis). In humans, the zygote stage is on Day 1 of week one post-fertilization until the cell will cleave into two new cells. The zygote stage is apparently the first stage of development of a multicellular eukaryote. Although a zygote is a product of the two cells joining together, it is a single cell with a nucleus consisting of chromosomes combined from the two parents. What does zygote mean? How does it differ from an embryo and a fetus? A zygote is basically a fertilized cell. In unicellular animals, the zygote can next undergo asexual reproduction to produce offspring. This condition is referred to as polyploidy. In some plants, the zygote can consist of more than two sets of chromosomes. The chromosomal set of the gametes has to be reduced to half so that when the gametes combine at fertilization the integrity of the chromosomal set can be maintained across generations. Gametes are essentially haploid for reproductive purposes. ![]() Thus, the result is a cell with twice the number of chromosomes. ![]() the union of the cytoplasms) and karyogamy (i.e. The successful entry of a sperm cell inside the egg cell leads to a series of events, particularly plasmogamy (i.e. Gametes are produced by gametogenesis the zygote is produced by the fusion of the male and female gametes. Instead, it disintegrates and is released during menstruation. Thus, the female gamete will not fully complete oogenesis and it will not attain maturity in the absence of fertilization. It should be noted though that the latter stage of oogenesis in humans occurs during fertilization. For example, in humans, the gametes have 23 chromosomes whereas non-sex cells (somatic cells) have 46. By haploid, it means the cell would have half of the usual set of chromosomes of a typical non-sex cell of the organism. Both of these processes produce haploid sex cells. In particular, the sperm cells are produced by male gametogenesis (called spermatogenesis) whereas the egg cells are produced by female gametogenesis (called oogenesis). The gametes are products of gametogenesis, which incorporates the process of meiosis. The difference between gamete and zygote lies in the number of chromosomal sets within their nucleus. However, they should not be used interchangeably as they have hugely different meanings. The cells that sprung from the zygote will essentially have the same genetic composition throughout the body but eventually will acquire a special role or a distinct function as they are organized into tissues, organs, and systems.īoth “ gamete” and “zygote” are common terms in biology. This newly formed single cell, then, undergoes a series of mitotic divisions and grows into a multicellular form. Their union will result in a zygote that is diploid (2n) and by a process called fertilization. In humans, the male gamete is the sperm cell and the female gamete is the ovum (also called the egg cell). Reproduction by sexual means involves male and female gametes. In biology, medical science, and other allied fields, including psychology, the term “ zygote” is used to refer to a cell that forms after the union of sex cells (also called gametes). What is a zygote? A zygote is a fertilized eukaryotic cell.
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