What is CROSS fertilization

Life exists and expands on planet Earth thanks to a fundamental function of living beings known as reproduction, through it an organism is capable of generating new living beings with the same or similar characteristics to the parent organism. Two ways are known reproduction: asexual and sexual. In nature, living beings with asexual or sexual reproduction and organisms that combine both modes of reproduction, such as plants and fungi, can be found.

In sexual reproduction, a female gamete fuses with a male gamete to form the zygote, this process is known as fertilization. In today's lesson at a Teacher we will tell you what is cross fertilization and we will see examples of it.

In the sexual reproduction always involved two different cells known as gametes, one male (called a sperm) and one female (called an egg), usually each cell is produced in a different individual, the sperm is generated in the sexual organs of a male and the ovum in the sexual organs of another. a female. But, in some cases, both types of cells are made in the same individual, let's see...

• unisexual organisms: The living being has a type of sexual organ: male or female.
• hermaphrodite organisms: In the same individual we can find both sexual organs: female and male.

What is fertilization? The fertilization It is the process by which the two cells, the egg and the sperm, come together to form the first cell of a new living being, known as an egg or zygote. There are different types of fertilization depending on the organisms involved:

• Cross fertilization: Fertilization in which each gamete or sexual cell comes from a different individual or, two individuals that produce both types of gametes fertilize each other.
• Self fertilization: When the two gametes come from the same organism.

The cross fertilization is also known as allogamy. It occurs when each gamete or sexual cell comes from a genetically different individual. In some particular cases, it can happen that two individuals produce both types of gametes (hermaphrodites) and fertilize each other. In either case, the female gamete fuses with the male, giving rise to a new cell with complete genetic material.

Cross fertilization is type of sexual reproduction through which genetic material is exchanged between different individuals, it is the reason for the immense genetic variability of living organisms, it is the engine of the evolution of species throughout the different generations.

This type of fertilization is typical of animals, but it is also common in plants, fungi, algae and protozoa. The gametes involved in this type of fertilization may be the same or different:

• there is cross fertilization isogamic, where the participating gametes have the same shape and size,
• and cross fertilization anisogamic, where the fusing gametes are different in size, shape, and behavior.

Let's look at some examples of cross fertilization in plants and animals:

Plants with flowers

Inside of reproduction of flowering plants You should know that there are monoecious (hermaphrodite) and dioecious (unisexual) plants. In the monoecious we can find both types of sexual organs in the same plant, and the dioecious only have organs of a single sex in each individual.

• monoecious plants they produce both types of gametes, they normally reproduce by self-fertilization because the same flower has both types of sexual organs (hermaphrodites). But, we also find in this group examples of cross sexual fertilization. A plant can have both types of flowers, with male organs and with female organs. The male flowers are found in the highest part of the plant, in order to distribute the gametes more easily. males in the pollen grain by means of the wind and thus fertilize female flowers of other plants to ensure their diversity genetics. Examples of this are: corn, rice and wheat.
• In dioecious plants, we find male and female flowers in different individuals, they must be in the same environment for cross-pollination or fertilization to occur. In this group we can find the Kiwi, it is a climbing plant from China. This plant was introduced in New Zealand to be cultivated and marketed for its rich fruits. The name "kiwi" was given in this country due to the great similarity of the villi of the fruit with the native bird there, known by the same name as the fruit.

Cross fertilization in animals

In this category we can also find unisexual and bisexual or hermaphrodite animals. Let's see examples of cross fertilization in both cases:

• The land snails, earthworms, leeches and starfish, are some examples of animals that have hermaphrodite cross fertilization. What does this mean? These animals have both types of sexual organs: male and female. As in the case of plants with hermaphroditic flowers, they can self-fertilize, but they can also carry out cross-fertilization. Two individuals of the same species can mate by exchanging male and female gametes simultaneously.
• animals like fish, reptiles, birds and mammals (with some exceptions) are those that have, for the most part, sexual dimorphism. This means that each individual has a type of sexual organ: female or male. In order to exchange their gametes, some have specialized organs, they do it through intercourse or the release of gametes into the environment. In the case of some rays, fertilization is internal and occurs through copulation, they are oviparous, the egg with the embryo develops inside the female until she matures to be expelled.