The 4 types of sex cells
Human beings, like most other animals, are multicellular organisms that perpetuate our species through the type of reproduction we know as sexual. This type of reproduction results in the emergence of individuals with genetic characteristics from two individuals, something that gives species much greater variability than asexual reproduction offers.
For sexual reproduction to produce a new being, a certain type of cell must be fused: the sex cells or gametes . It is about these that we are going to talk in this article.
Gametes or sex cells
They receive the name of gametes or sexual cells to a certain type of cell which has the main function of generating a new being , perpetuating the species and the genes of the parents.
Sex cells have different forms, specifically two types whose union will generate the zygote from which a new individual will eventually develop. The specific name of these cells depends on the type of living being we are talking about, one being male and the other female.
This type of cell has half the number of chromosomes of the species in question , which, when the new being appears when two cells from two different individuals join or merge, allows the child organism to have the same number of chromosomes as its parents, although with different genetic information from that of any of the previous ones. After their union, a genetic recombination of the genetic information from both cells takes place, generating a unique genetic code through this recombination.
In the case of the human being, we have a total of 46 chromosomes divided into 23 pairs. Of these, 22 of the pairs correspond to somatic chromosomes and are equal regardless of gender. However the 23rd pair differs between men and women , these being the sex chromosomes that mark our genetic sex. Specifically, the male has one X and one Y chromosome, while the female has two X chromosomes.
Sex cells in animals
When we talk about sex or sex cells, the first thing we think about is the type of reproduction and cells that we human beings have and which are also possessed by the rest of animal species: sperm and eggs.
Sperm are the male sex cells that possess half of the genetic information needed to form a new living being. It is a type of cell of very small size, inferior to that of the female gametes, and which is formed in great quantity inside the testicles of the males of each species.
For fertilization to take place, sperm must travel to the egg, of which only one (usually, although there are exceptions) will manage to enter the egg and combine its genetic material with it. This is why the spermatozoon has morphological adaptations that allow such movement.
Its basic morphology is as follows:
Firstly, we can observe the existence of a large head (the largest part of the spermatozoon) within which we can find the nucleus , in which the genetic information in question can be found, and the acrosome or layer formed by various enzymes that allow the spermatozoon to enter the female gametes. In addition, we can find different substances that nourish and allow the movement of the spermatozoon.
The other main part is the tail or flagellum, thanks to which the sperm can travel inside the female body until they reach the egg. Inside it we can find firstly a small neck through which it joins the head, then an intermediate piece in which we can find different mitochondria , which allow the production of enough energy (through the substances present both in the sperm itself and in the rest of the semen) and finally the flagellum or final part, which moves to allow the displacement.
Eggs are the female sex cells, which carry half of the genetic information needed for the genesis of a new being. It is a type of large cell, which are shaped like a sphere and which are produced by the ovaries of the females of different species .
Ovums have the characteristic that they are not always available for fertilization. There is a whole cycle through which an ovum is produced, matures, remains available for possible reproduction and is released if it is not fertilized, this being the menstrual cycle. Approximately one is generated per month (in reality, it is usually 28 days).
Also, unlike sperm that are present in large numbers throughout life, there are only a certain number of them in each female. During reproduction, the egg itself remains immobile until the sperm reach it and finally penetrate it (if at all).
The structure of this cell is as follows, from the inside to the outside:
First and foremost, the nucleus in which the genetic information that would allow the formation of a new being to join a spermatozoon is found. We can also find inside it the yolk , a series of substances as an energy reservoir that would allow the survival of the zygote until the formation of a placenta. All of this would be surrounded by a plasma membrane that limits the cell and through which chemical elements can enter and leave, allowing its interior to be chemically balanced.
Around the membrane we can find a protective gelatinous layer, called the pellucid layer , which acts as a shield while allowing the entry of a first spermatozoon and ends up hardening to prevent more than one from entering. The last layer, the outermost one, is the radiata crown. This will have special relevance in regulating the sexual hormones and generating the placenta if there is fertilization.
Sex cells in vegetables
Sperm and ova are not the only types of sex cells that exist, being only those of animals. Plants and other vegetables also have in many cases sexual reproduction , being their sex cells the oosphere and pollen.
The oosphere is the name given to the type of female sex cell in plants that have the ability to reproduce sexually. This type of cell can be found inside the so-called seminal rudiments located in the embryonic sacs of plants, located in the flowers.
Like animal eggs, it has half the chromosomes of the remaining cells of individual parents. The pollen or male gamete at the plant level comes into contact with it through the stigma of the flowers.
Pollen would be the vegetable equivalent of sperm: the male sex cell of plants. These are small particles in the form of grains that are formed in the stamens of plants. It joins the oosphere in the process known as pollination (for which they need the wind or the help of animals.
These grains, which contain half the genetic information needed to produce a new being, enter the stigma and bind to the oosphere. Once in the stigma, the pollen generates a small extension called a pollen tube in order to transport its genetic material to the oosphere.