Zygotes are the first cells of new organisms. Stages of development of the zygote

An elementary unit of all life on Earth is a cell. It is the formation of new cells that allows the body to grow and develop. The life activity and structure of these units is very difficult and depends on the specific nature of the destination.

The appearance of the term "zygote"

The appearance of the term "zygote" is a merit of the German scientist Edward Strasburger, who devoted his entire life to the study of cytology and the chromosome theory of heredity. It was he who at the end of the nineteenth century first came to the conclusion that cell division in the plant, animal and human organism occurs approximately according to the same scheme.

Zygote: Definition

Sex cells (gametes) perform a reproductive function, that is, due to their presence in the body, sexual reproduction is possible. Female gamete is an ovum, male is sperm. Each sex cell has a haploid (single) set of chromosomes.

The concept of "ontogeny" includes all stages of the development of the organism from birth to death. Its beginning is the fertilization, that is, the fusion of the sperm and the egg, resulting in the formation of a zygote. It contains hereditary information received from both parents. What is a zygote? Biology gives an accurate definition of this concept. We will examine it in detail.

So, the zygotes are diploid cells, which are formed by the fusion of gametes. Diploidity is due to a complete (double) set of chromosomes, equally obtained from the father and mother gametes. The development of the zygote begins immediately after the fertilization process, which is also called fertilization.

Crushing of the zygote

Upon completion of the process of fertilization, the resulting cell moves to the uterus. Along the way, development and fragmentation of the zygote begin to occur. This is a complex process, consisting of several stages.

Between the moment of fertilization and the first mitotic division takes approximately 30 hours. This is the time when all the preparatory processes take place in the female body, without which the development of a new organism is impossible. To prevent the further formation of the embryo, there are various factors affecting the state of the woman's body. These factors include chromosomal mutations, an incorrect lifestyle of the mother (use of alcohol, drugs, smoking), the use of certain drugs, severe viral diseases, etc.

A fetus develops from the zygote. The first stage of this process is fragmentation. This is not an accidental name. After all, between the divisions there is no stage of cell growth, that is, as a result of each of them, the cells decrease in size exactly in half, becoming smaller. The daughter cells, formed by splitting the zygote, are called "blastomeres". The process of fragmentation lasts until the moment when the fetus is formed from it. Thus, it can be said that the human body appears as a result of a multibillion-dollar division of the zygote.

Blastula and gastrulation

Blastomers consist of two layers. The outer is adjacent to the transparent shell. It is called the trophoblast (nourishing leaf), and the outer one is the embryoblast (embryonic leaf). Gradually, in the process of multiple division, a cavity forms between these two layers, inside of which a fluid accumulates. This moment is the phase of the blastula.

Reproduction of cells of the embryoblast is accompanied by its growth along the wall of the cavity. As a consequence, a second layer of the embryoblast appears, which forms a yolk vial. Simultaneously with this process, a fetal embryo, grouped at one of the poles, is formed from the main mass of embryoblasts. It is at this stage that the embryo reaches the uterus. In the future, it is released from the transparent shell and implantation.

Trophoblast plays an important role in this process, because its cells, having proteolytic properties, melt the epithelium at the site of attachment of the embryo to the mucous membrane of the uterus. As a result, the epithelium becomes a milk-like mass.

Stages of development of the zygote quite quickly replace each other. Blastula turns into a gastrula, which is a two-layer ball. The outer layer is the ectoderm, the lower one is the endoderm.

Organogenesis

Zygotes are the first cells of new organisms. The entire set of organs necessary for life is initially formed from them. The process of organ formation itself is called organogenesis. Its beginning is marked by the formation of the neural plate, which occurs in the ectoderm on the dorsal side of the embryo. Further, there are rudiments of other organs and systems: the skin and the nervous system (from the ectoderm); Digestive and respiratory system (from the endoderm); Musculoskeletal system, blood, excretory and reproductive systems (from the mesoderm). Further, before the moment of birth, these systems develop and improve.

Post-embryonic development

This period begins from birth until the onset of puberty. Depending on the level of organization of organisms, there are two types of embryonic development.

1. Direct development. In this case, the child is similar in appearance and internal characteristics to his parents. Differences consist in the size and underdevelopment of some organs. Characteristic for birds and mammals, including humans.
2. Indirect development. With this type of development, the child (larva) has many differences with the parents. Characteristic for frogs and insects.

Zygotes are cells that duplicate the genotype of parents. But in the process of developing the embryo cells begin to differ in structure and perform various functions. This is due to the fact that some types of genes function in some cells, and others in others. Thus, the body is a complex system, based on the zygote.