Since ancient times, people marvel at the beauty and diversity of the surrounding plants, especially flowers.Their flavor and tenderness in all ages have been the personification of love, purity, expression of feelings.Gradually, people realize that you can not just enjoy the existing species of these wonderful creatures, but also to take part in their formation.Thus began the era of plant breeding, leading to the production of new species having a necessary and important features in the genotype and phenotype.Two science, are working together on this issue, managed thus far to achieve a fantastic result - it's genetics and botany.
subject of study Botany
Botany - the science that studies everything about plants.That is, they:
This discipline covers all aspects of flora, since the internal processes of respiration, photosynthesis and reproduction, and ending with a variety of external phenotypic traits.
This is one of the oldest sciences, which appeared with the development of human rights.Interest in growing creatures around him, so decorating the surrounding area, was always a person.Moreover, in addition to beauty, it has always been a more powerful source of food, medicinal components, building material.Therefore, botany - is the science that studies the most ancient, important, diverse and complex organisms on the planet - plants.
With the passage of time and the accumulation of theoretical knowledge about the structure of these creatures from the inside, their way of life and the processes occurring in them, became available and an understanding of how to manipulate their growth and development.It is gaining momentum science genetics, which allows for chromosomal study different objects to cross them with each other, receive good and bad results, choose a profitable and necessary.This was made possible thanks to the following discoveries.
- double fertilization in plants.
- open process of mitosis and meiosis.
- Development of methods of crossing.
- heterosis, inbreeding and outbreeding.
- Deciphering the genetic code of plants.
- Biomolecular studies of the composition of tissues and cells.
- discoveries in the field of cytology and histology.
Of course, that's not all prerequisites that marked the beginning of a powerful movement and development work on methods of breeding plants.
Crossing and its characteristics
Another name for the process of crossing - hybridization.The method of using this phenomenon is called hybridological.His first he applied for his experiments Gregor Mendel.His famous experiments on peas every schoolboy knows.
essence of the whole process is a cross between the parental forms in order to obtain heterozygous offspring on the basis of which will be called a hybrid.This type of crossing designed different.They are chosen based on the individual characteristics of the variety, species or genus.There are currently two main types of such processes.
- Outbreeding or outbreeding. Assumes that the initial parental forms do not belong to the same species, genus or class.That is not to have any kinship.This crossing is one of the most popular and most often leads to heterosis in the breeding of pure lines.
- inbreeding or inbreeding - hybridization of closely related species belonging to the same species or genus, class.This method is used for fastening in a population of any useful feature, including phenotypic.When properly carried out repeated inbreeding is possible to obtain pure genetics plant lines.
These types of crosses have more narrow varieties inside.Thus, one form of outbreeding considered crossbreeding - Hybridization between varieties.
addition types, allocate more and different kinds of cross-breeding.They were described in detail and studied even Mendel, Thomas Morgan and other geneticists past centuries.
There are several basic types of hybridization of animals.
- Monohybrid or simple.It involves crossing parental forms to give the first offspring, once held.
- two-hybrid - taken as a basis the parents differ in the two pairs of signs.
- Return - a hybrid of first generation crosses with the original parent individuals.
- Poligibridnoe, or double - the first generation of individuals continue to hybridize with each other, and later with other varieties and species.
All species have a value specified in each specific situation.That is enough for some plants simply crossing to get the desired result.But others require a complex phased poligibridnaya hybridization to produce a desired trait and secure it in the general population.
hybrids of different generations
a result of any crossing formed or that the offspring.Traits that it took the parents are able to manifest itself in varying degrees.
Thus, signs of first-generation hybrids are phenotypically always uniform, as evidenced by the law of Mendel (the first) and his experiments on peas.So often to get the same result that you want all at once, use it monohybrid kind of hybridization.
Further, all subsequent specimens already combine the properties, so there is splitting in certain ratios.Manifest recessives interfere mutational processes.Therefore, the most important in human industrial activity, its agriculture, is just the first generation of plants obtained.
typical example: if the aim is to obtain a yellow tomatoes only a result of one seasonal period, the cross should be yellow and red tomatoes, but it must be red previously obtained from yellow parent.In this case, the first generation will certainly be uniform - yellow tomato fruit.
characterization of interspecific hybrids are those which are obtained by outbreeding or distant crossing.That is the result of the mating of individuals belonging to different species, in order to obtain new with predetermined characteristics and properties.
In this way, people in the industry were obtained many important agricultural and ornamental plants, and breeding animals bred many new kinds of animals.
Examples of such organisms
Examples of interspecific hybrids among plants:
- zernokormovaya wheat;
- triticale - wheat and rye;
- rye-wheatgrass forms;
- several other types of tobacco.
Speaking of animals, as many representatives can cite as an example:
- mules (horse and donkey);
- liger - a lion and a tiger;
- rackelhahn - grouse and capercaillie, and others.
main problem these hybridizations that offspring or sterile or non-viable.That's why people have created and developed a lot of ways to address these factors.After all, if the desired result is obtained, it is very important not just to fix it, but also put into the system to obtain such organisms.
What causes sterility of interspecific hybrids?
reasons for these problems are rooted in the processes of mitosis and meiosis, namely in anaphase, when the chromosomes disperse the poles of the cell.At this point, each of them seeking their homologous pair.Since forming the whole chromosome and chromatid consists of a common karyotype of an organism.
But those individuals whose fusion occurred from different parental forms, the ability to meet such structures is minimal or impossible.That is why going on a random combination of characters and as a result individuals become sterile or non-viable.That is, the genes are, in fact, become incompatible.
If we look at the molecular level and find out the reason for sterility of interspecific hybrids, the answer is: it is the incompatibility of DNA from the cell nucleus and mitochondria.As a result, there is no conjugation of chromosomes in meiotic process.
This leads to disastrous results in plant breeding and in crossing and breeding of new breeds and species.Most often this happens at the flora.Therefore, get a crop of hybrid plants is possible only once, which is very inconvenient for the development of agriculture.
After scientists became clear the reason for sterility of interspecific hybrids, the active work to find ways to eliminate these causes.This led to the creation of several ways to eliminate sterility individuals.
Ways of overcoming infertility
main way that have chosen to address the problems of biology, as follows.At the stage of meiosis, when chromosomes disperse to poles of the cell, it introduced a special substance - colchicine.It promotes the dissolution of yarn spindle (cell center).As a result of all chromosomes remain in a single cell and not fall into different.Now available free conjugation between homologous pairs, and therefore, it is a normal process of meiosis in the future.
thus becomes a fertile offspring and easy fruiting later in crosses with different forms.Most often, this method is used in plant breeding, he has called polyploidy.It was first applied to our scientists Karpechenkovym.So he got the first fertile hybrid of cabbage and radish.
What causes sterility of interspecific hybrids, we have already found.Knowing the nature of the problem, it was possible to create two more ways to solve it.
- Plants pollinated by pollen of one parent only.This method allows several generations of hybrid animals, fertile.But then all the same indication is returned, and individuals again become sterile.
- Pollination hybrids in the first generation pollen parents.
Today, more methods of struggle are not created, but work in this direction are carried out.
Lilies and their hybrids
symbol of purity and innocence, the flowers of sorrow and grief for the departed, the representatives of the gentle and delicate lily - lily.These plants are valued by man for many centuries in a row.During this time, only some varieties have not been established!Naturally, the interbreeding touched them, too.
result was the elimination of nine groups of hybrid varieties which are staggering beauty of phenotypic traits!Among them a special place is occupied by two of the most unusual and popular representative:
- Oriental hybrids;
- FROM lily hybrids.
Consider symptoms in both groups and give them a description.
It is the largest of the emerging hybrid flower.Biology them practically does not differ from that of other members.Dimensions growing cups can reach 31 cm in diameter, and the color is different.Very beautiful variety of Nippon, having large white flowers with pink trim.Petals have crimped.
The height of these plants range up to 1.2 m. This allows them to plant at a distance of 20-25 cm from each other and create a beautiful blooming range.All members of this group exude a very strong flavor.
This is the OT-hybrid lily, which is an acronym formed from the full title: oriental-tubular shape.They are called lily trees in a very high amount of plants and large flowers.On one stalk up to 2.5 meters can be formed more than 25 large (30 cm) flowers that are very fragrant and brightly colored.
This allows this group of hybrids to be very popular among gardeners, although not everyone can cope with their breeding.It takes very good care and proper landing that such forms could settle down and produce offspring.
Sunflower and its hybrid forms
sunflower hybrids differ in ripening seeds.Thus, the release:
- maturing (90 days);
- early ripening (up to 100 days);
- is middle (up to 110 days).
Seeds hybrids also provide unequal.Oil content and yield and depends on the different ripening.The longer a plant in the ground, the higher the quality of the crop.You can call some of the most popular in the world of hybrids of this plant, the most popular in agriculture.
Among their main advantages:
- resistance to drought;
- diseases and pests;
- high quality seeds;
- good fruiting.