What is the cause of infertility of interspecific hybrids? Examples of interspecific hybrids

From the earliest times people were fascinated by beauty anda variety of surrounding plants, especially flowers. Their fragrance and tenderness have been the embodiment of love, purity, and feelings. Gradually the person realized that he could not simply enjoy the already existing types of these beautiful creatures, but also take part in their formation. Thus began the era of plant breeding, leading to the acquisition of new species that have more necessary and important features in the genotype and phenotype. Two sciences working together on this issue have managed to achieve simply fantastic results by now - genetics and botany.

The subject of botany

Botany is a science that studies everything about plants. That is their:

morphology;
genetics;
physiology;
anatomy;
systematics.

This discipline covers all aspects of the life of the representatives of the flora, beginning with the internal processes of respiration, reproduction and photosynthesis, and ending with an external diversity of phenotypic traits.

This is one of the most ancient sciences that appearedtogether with human development. Interest in the surrounding creatures around him, so decorating the surrounding space, was a man always. Besides, besides beauty, this at all times was also a powerful source of food, medicinal components, building material. Therefore, botany is a science that studies the most ancient, important, diverse and complex organisms on our planet - plants.

Plant breeding

With the passage of time and the accumulation of theoreticalknowledge of the structure of these creatures from within, their way of life and the processes that are taking place in them, the understanding of how their growth and development can be manipulated has become accessible. The science of genetics, which allowed to study different objects on a chromosomal level, to cross them among themselves, to get bad and good results, to choose beneficial and necessary ones was gaining momentum. This was made possible by the following discoveries.

Double fertilization in plants.
The discovery of processes of mitosis and meiosis.
Development of methods of crossing.
The phenomena of heterosis, outbreeding and inbreeding.
Decoding of the genetic code of plants.
Biomolecular studies of the composition of cells and tissues.
Discoveries in the field of cytology and histology.

Of course, these are not all the prerequisites that have led to a powerful movement and development of selection methods for working on plants.

Crossing and its characteristics

Another name for the process of crossing -hybridization. The method of using this phenomenon is called a hybridologic method. Gregor Mendel used it first for his experiments. His famous experiments on peas are known to every schoolboy.

The essence of the whole process is to crossamong themselves parental forms in order to obtain a heterozygous for the offspring, which will be called a hybrid. The types of crossing are different. They are selected taking into account the individual characteristics of the variety, species or genus. There are basically two main types of such processes.

Outbreeding, or unrelated crossing. Implies that the initial parent formsdo not belong to the same species, genus or variety. That is, they do not have family ties. This crossing is one of the most popular and most often leads to heterosis in the derivation of clean lines.
Inbreeding, or inbreeding - closely related hybridization of individuals,belonging to the same species or genus, variety. This method is used to fix in the population of any useful attribute, including phenotypic. With a multiple correctly performed incrustation, it is possible to obtain genetically pure plant lines.

These types of crossing have narrower varieties within themselves. So, one of the forms of outbreeding is cross-breeding - hybridization between varieties.

In addition to types, different types of crosses are also distinguished. They have been described in detail and studied by Mendel, Thomas Morgan and other genetics of past centuries.

Types of crossing

There are several main types of hybridization of individuals.

Mono-hybrid, or simple. It implies the crossing of parental forms with the receipt of the first offspring, is carried out once.
Dihybrid - the basis is taken by parents, differing in two pairs of characteristics.
Recurrent - a hybrid from the first generation is crossed with the original parent.
Polyhybrid, or double - individuals of the first generation are further crossed among themselves, and subsequent with other varieties and species.

All the indicated varieties are of importance inevery situation. That is, for some plants, a simple crossing is sufficient to obtain the desired result. And for others, a complex phased poly hybrid hybridization is required to obtain the desired trait and fix it in the entire population.

Hybrids of different generations

As a result of any crossing, this or that offspring is formed. The traits that it took from parents are capable of manifesting themselves in uneven degrees.

So, the signs of hybrids of the first generationare phenotypically always uniform, which is confirmed by Mendel's law (first) and his experiments on peas. Therefore, often to obtain the same result, which is required only at times, the mono-hybrid type of hybridization is used.

Further, all subsequent individuals are already combined inproperties, therefore splitting occurs in certain ratios. Recessives appear, mutation processes interfere. Therefore, the most important generation of plants is the most important for the industrial activity of man, his agriculture.

A typical example: if the goal is to obtain only yellow tomatoes as a result of one seasonal period, then a yellow and red tomato should be crossed, but red must be obtained earlier from the yellow parent. In this case, the first generation, of course, will be uniform - the yellow fruits of tomatoes.

Interspecific hybrids: characteristic

Interspecies call those hybrids that receiveas a result of outbreeding or distant crossbreeding. That is, it is the result of pairing individuals belonging to different species, in order to obtain a new one with predetermined characteristics and properties.

In this way in industry many important agricultural and ornamental plants were obtained by humans, and many new species of animals were selected for animal breeding.

Examples of such organisms

Examples of interspecific hybrids among plants:

wheat fodder;
triticale - wheat and rye;
rye-grassy forms;
wheat-elmus;
several kinds of tobacco and others.

If we talk about animals, then many representatives can be cited as an example:

a horse (a horse and a donkey);
ligra - lion and tigress;
meadow - grouse and wood grouse and others.

The main problem of such hybridizations is,that the offspring is either infertile or unviable. That's why people created and developed a lot of ways to eliminate these factors. After all, if the desired result is obtained, it is very important not only to fix it, but also to introduce such organisms into the system.

What is the cause of infertility of interspecific hybrids?

The causes of such problems lie in the processes of meiosisand mitosis, namely in anaphase, when the chromosomes diverge to the poles of the cell. At this point, each of them is looking for a homologous pair. So whole chromosomes are formed from chromatids and the common karyotype of the organism is formed.

But for those individuals who have had a fusionfrom different parental forms, the possibility of meeting such structures is minimal or impossible. That is why there is an accidental combination of symptoms and as a result the individuals become infertile or unviable. That is, genes, in fact, become incompatible.

If we turn to the molecular level and find out,the reason for the infertility of interspecies hybrids, the answer is this: this is the incompatibility of DNA sections from the cell nucleus and mitochondria. As a result, there is no conjugation of chromosomes in the meiotic process.

This leads to deplorable results both inplant breeding, and in crossing and breeding of rocks and new species of animals. Especially often this happens in the representatives of the flora. Therefore, it is possible to obtain a crop of hybrid plants only once, which is extremely inconvenient for the development of agriculture.

After the scientists became clear what the reasoninfertility of interspecies hybrids, active work has begun to find a way to eliminate these causes. This led to the creation of several ways to eliminate the sterility of individuals.

Ways to overcome infertility

The main way, which was chosen to solve thisproblems of biology, the next. At the stage of meiosis, when the chromosomes diverge to the poles of the cell, a special substance, colchicine, is introduced into it. It promotes the dissolution of the filament spindle (cell center). As a result, all chromosomes remain in the same cell, and do not fall into different cells. Now, a free conjugation between homologous pairs is possible, and hence a completely normal meiosis process in the future.

Thus, the offspring become fertile andeasily fructifies in the future with crosses with different forms. Most often this method is used in plant breeding, it has the name polyploidy. For the first time it was applied by our scientist Karpenchenkov. So he received the first fertile hybrid of cabbage and radishes.

What is the cause of infertility of interspecies hybrids, we have already found. Knowing the nature of the problem, it was possible to create two more ways to solve it.

Plants pollinate only one of the pollenparents. This method makes it possible to obtain several generations of hybrid individuals, fertile. However, the sign will then return anyway, and the individuals will again become sterile.
Pollination of hybrids in the first generation by pollen of parents.

Today, more methods of struggle have not been created, but work is being done in this direction.

Lilies and their hybrids

A symbol of purity and innocence, flowers of sadness andmourning for the departed, tender and subtle representatives of the lily - lily. These plants are valued by man for many centuries in a row. During this time, what sorts of varieties have not been created! Naturally, interspecific crossings touched them, too.

The result was the withdrawal of nine groupshybrid varieties that simply amaze the beauty of phenotypic signs! Among them, a special place is occupied by the two most unusual and popular representatives:

eastern hybrids;
lily OT-hybrids.

Consider the characteristics of both groups and give them a characterization.

Eastern hybrids

This is the largest hybrid in the emerging flower. Biology of them practically does not differ from that of other representatives. Dimensions of the growing cup can reach 31 cm in diameter, and the color varies. Very beautiful is the variety Nippon, which has white large flowers with a pink edging. Their petals are corrugated.

The height of these plants varies up to 1.2 m. This allows you to plant them at a distance of 20-25 cm from each other and form beautiful flowering ridges. All representatives of this group exude a very strong flavor.

Orienpity

This is the lily of OT-hybrids, the abbreviation of whichis formed from the full name: oriental-tubular forms. They are also called lily trees for the very high size of plants and large flowers. A single stem up to 2.5 meters high can form over 25 large (up to 30 cm) flowers that are very fragrant and brightly colored.

This allows this group of hybrids to be verydemanded by gardeners, although not everyone is allowed to cope with their breeding. It requires very careful care and proper disembarkation, so that such forms can take root and give offspring.

Sunflower and its hybrid forms

Hybrids of sunflower differ from each other by the maturation of seeds. So, allocate:

early maturing (up to 90 days);
early maturing (up to 100 days);
mid-ripening (up to 110 days).

Seeds also give hybrids different. Oil productivity and yield is different and depends on the maturity. The longer the plant in the ground, the higher the quality of the crop. You can name a few of the most common hybrids in the world of this plant, the most in demand in agriculture.