The 4 types of sex cells

Human beings, like most other animals, are multicellular organisms that perpetuate our species through the type of reproduction that we know as sexual. This type of reproduction, which results in the emergence of individuals with genetic characteristics coming from two individuals, something that gives the species a much greater variability than that offered by the asexual reproduction.

For sexual reproduction to produce a new being it will be necessary for a certain type of cells to fuse: sex cells or gametes. It is about these that we are going to talk in this article.

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Gametes or sex cells

They receive the name of gametes or sex cells to a certain type of cell which Its main function is to generate a new being, perpetuating the species and the genes of the parents.

Sex cells have different shapes, specifically finding two types whose union will be the one that generates the zygote from which a new individual will develop. The specific name of these cells depends on the type of living being we are talking about, there being a male and a female.

This type of cells has half the chromosomes of the species in question, something that when the new being appears before the union or fusion of two cells from two different individuals allows the child organism to end having the same number of chromosomes as their parents, although with different genetic information from either of the previous. After their union, a genetic recombination of the genetic information from both cells occurs, generating a unique genetic code through said recombination.

In the case of humans, we have a total of 46 chromosomes divided into 23 pairs. Of these, 22 of the pairs correspond to somatic chromosomes and are the same regardless of sex. However par 23 differs between men and womenThese 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.

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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 humans have and we also have the rest of animal species: sperm and ovules.

Sperm

Called sperm to the sex cells of the male gender, and which have half of the genetic information necessary to form a new living being. It is a type of cell of very small size, smaller than that of female gametes, and which are formed in large numbers within the testes of the males of each species.

For fertilization to occur, it is necessary for the sperm to travel to the ovum, of which only one (in general, although there are exceptions) is going to get into the egg and combine its genetic material with he. That is why the sperm has morphological adaptations that allow such displacement.

Its basic morphology is as follows:

First of all we can observe the existence of a large head (the largest part of the sperm) 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 sperm to enter the gametes female. In addition to this, we can find different substances that allow us to nourish and allow the movement of the sperm.

The other main part is the tail or flagellum, thanks to which the sperm can move through the interior of the female body until they reach the ovum. Inside it we can first find a small neck through which it joins the head, later an intermediate piece in which we can find different mitochondria, which allow the production of sufficient energy (through the substances present in both the sperm itself as in the rest of the semen) and finally the flagellum or final part, which moves to allow the displacement.

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Ovules

Eggs are female sex cells, which carry half of the genetic information necessary for the genesis of a new being. It is a type of large cell, which is shaped like a sphere and are produced by the ovaries of the females of the different species.

The ovules present the characteristic that they are not always available for fertilization, and there is a whole cycle through which they are produces an ovum, matures, remains available for possible reproduction and is shed if it is not fertilized, this being the cycle menstrual. It is generated approximately one per month (actually, it is usually 28 days).

Also, unlike sperm that are present in large numbers throughout life, there is only a certain number of them in each female. During the reproduction itself the ovum remains immobile, until the spermatozoa reach it and finally the union manages to penetrate it (in case it is achieved).

The structure of this cell is as follows, from the inside out:

In the first place and inside, the nucleus in which is the genetic information that would allow the formation of a new being to join a sperm stands out. We can also find yolk inside, a series of substances as an energy reservoir that would allow the zygote to survive until the formation of a placenta. All this would be surrounded by a plasma membrane that limits the cell and through which chemical elements can enter and leave that allow its interior to be chemically balanced talking.

Around the membrane we can find a protective gelatinous layer, called pellucid layer, which acts as a protection at the same time that it allows the entry of a first sperm and ends up hardening to prevent more than one from entering. A last layer, the outermost, is the corona radiata. This will have special relevance in regulating sex hormones and generating the placenta if there is fertilization.

Sex cells in plants

Sperm and ovules are not the only types of sex cells that exist, being only those of animals. Plants and other plants also have sexual reproduction in many cases, being its sexual cells the oosphere and pollen.

The oosphere

The oosphere is the name of the type of female sex cell in plants that has the ability to reproduce sexually. This type of cell can be found inside the so-called seminal rudiments located in the embryo sacs of plants, located in flowers.

Like animal ovules, it has half as many chromosomes as the rest of the cells of the parent individuals. The pollen or male gamete at the plant level comes into contact with it through the stigma of the flowers.

The pollen

Pollen would be the plant equivalent of sperm: the male sex cell of plants. These are small, grain-like particles that form in the stamens of plants. Joins the oosphere in the process known as pollination (For which they need the wind or the help of animals.

These grains, whose content is half of the genetic information necessary to produce a new being, enter the stigma and join the oosphere. To do this, once in the stigma, the pollen generates a small extension called the pollen tube in order to transport its genetic material to the oosphere.