The biological significance of meiosis is to preserve in sexual reproduction of permanent diploid set of chromosomes in all generations of organisms

Fertilization in humans

The biological significance of meiosis is to preserve in sexual reproduction of permanent diploid set of chromosomes in all generations of organisms of a certain type. As a result of the merger of male and female gametes with a haploid set of chromosomes (this process is called a fertilization) occurs a new body with a double set of chromosomes, i.e. resumes diploid set that is typical for somatic cells.

The fertilized egg is called a zygote (from Greek “a pair connection”). Its subsequent division leads to the formation of the human organism, each cell of which stores the double set of chromosomes. The zygote contains one chromosome from the father, and the other — from the mother in each pair of chromosomes (diagram 105). This predetermines the similarity of the child with his parents.

Gender of new organism depends on which male gamete has fused with the egg. If it contained the X-chromosome, the zygote will develop into the woman's body, if the Y-chromosome — into the male.

Fertilization — is the process of merging of the sperm with the egg, resulting in a zygote. At this point, resumes a diploid set of chromosomes. Taken from http://worldofschool.org

Diagram 124. Diagram of fertilized egg development: 1 — mature egg; 2 — fertilization; 3-5 — cleavage; 6 — implantation; 7 — sperm
Diagram 125. Fertilization: 1 — egg; 2 — sperm; 3 — penetration of one spermatozoid into the egg; 4 — fusion of egg genetic material (23 chromosomes) and sperm’ (23 chromosome) to form a zygote; 5 — zygote

To make fertilization happen, there undergoes a lot of different processes. First of all, between a man and a woman should be held sexual intercourse, in which sperm gets deep into the woman's vagina. Its amount should be not less than 3 mm, and its content of sperm is not less than 20 million per milliliter. They must be sufficiently mobile and active, and fallopian tubes — passable.

Once got inside the vagina, the sperm move to the uterus, and then — to the fallopian tube (diagram 124) at a rate of 3 mm per minute, where they meet a mature egg. In the fallopian tube, closer to the vial, millions of sperm are “attacking” an egg, but only one can penetrate it. Then occurs merge of egg and sperm nuclei (diagram 125). From this point, which is the beginning of ontogenesis, begins existence of a new organism.

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Questions:
  • Determine the basic biological nature of fertilization.

  • Analyze the process of fertilization.

  • How many sperm penetrate the egg?