Biological species species criteria. Species and its ecological characteristics. Object of study - karyotype

In biology, a species is a certain set of individuals that have a hereditary similarity of physiological, biological and morphological features, are able to freely interbreed and produce viable offspring. Species are stable genetic systems, because in nature they are separated by some series of barriers from each other. Scientists distinguish between them according to a number of basic features. Usually, the following species criteria are distinguished: morphological, geographical, ecological, genetic, physico-biochemical.

Morphological criterion

Such signs are the main ones in this system. Morphological criteria of a species are based on external differences between individual groups of animals or plants. This condition subdivides into species organisms that clearly differ from each other in internal or external morphological features.

Geographic criteria of the species

They are based on the fact that representatives of each stable genetic system live within limited spaces. Such areas are called areas. However, the geographical criterion has some shortcomings. It is not universal enough for the following reasons. First, there are some cosmopolitan species that are distributed all over the planet (for example, the orca whale). Secondly, in many biological aggregates, the ranges coincide geographically. Thirdly, in the case of some too rapidly dispersing populations, the ranges are very variable (for example, a sparrow or a house fly).

Ecological criterion of the species

It is assumed that each species is characterized by certain characteristics, such as the type of food, timing of reproduction, habitat, and everything that determines the ecological niche it occupies. This criterion is based on the assumption that the behavior of some animals differs from the behavior of others.

Genetic criterion of the species

This takes into account the main property of any species - its genetic isolation from others. Plants and animals of different stable genetic systems almost never interbreed. Of course, a species cannot be completely isolated from the influx of genes from related species. However, at the same time, he generally retains the constancy of his genetic composition for a really long period of time. It is in the genetic component that the clearest differences between representatives of different biological populations lie.

Physico-biochemical criteria of the species

Such criteria also cannot serve as an absolutely reliable way to distinguish between species, since fundamental biochemical processes
occur in similar groups in the same way. And in the environment of each individual species there is a certain number of adaptations to certain living conditions, which affects the change in biochemical processes.

conclusions

Thus, according to some single criterion, it is very difficult to distinguish between species. The belonging of an individual to any particular species should be determined only through a comprehensive comparison according to a number of criteria - all or at least the majority. Individuals that occupy a certain territory and are able to freely interbreed with each other are a species population.

Species criteria determine how pronounced the traits and properties that distinguish one species from another.

A species is considered to be a historically formed association of populations, where individuals are endowed with genetic conformity, morphological, physiological similarity, freedom of interbreeding and further reproduction, stay in a certain area in special living conditions.

Genetic (genetic-reproductive) criterion of the species

Genetic connection is the initial reason for the external similarity of organisms and the primary sign for combining into a separate set of individuals.

Individuals within the same species are characterized by a certain set of chromosomes, their quantitative value, size and external outlines.

The cytogenetic criterion is the most important feature of the species. Due to the different sets of chromosomes, living organisms different types adhere to a special isolation in the production of offspring and do not have the opportunity to interbreed.

The study of the shape and number of chromosomes is performed using the cytological method. Number of structural elements cell nucleus- a distinctive feature of the species.

Morphological criterion of the species

According to the morphological method, individuals of the same species are combined according to similar shape and structure. By appearance black and white crows are classified as different species.

Morphological features are one of the main, but often not decisive. In nature, there are groups of organisms that have common external features, but not crossing. They are twin species.

An example is the varieties of mosquitoes, previously classified as malarial. They are distinguished by a dissimilar food base, referring individuals to different ecological niches.

Ecological criterion of the species

Participation in the individual habitat is a fundamental principle of the ecological criterion.

One type of mosquito feeds on the blood of mammals, the other - birds, the third - reptiles. However, some populations of insects serve as carriers of malaria, while others do not.

Accordingly, two different species cannot coexist within the same ecological niche, but different living organisms of the same species can live in dissimilar habitats. Groups of these homogeneous populations are called ecotypes.

Physiological (physiological-biochemical) criterion of the species

The physiological criterion is manifested in connection with the peculiarities of the complex complex of the vital activity of the organism and its individual systems. According to this classification, individuals are grouped according to the similarity of their reproductive processes.

Organisms outside of the same species are practically incapable of interbreeding or produce infertile offspring. But there are individual representatives that are capable of reproduction and give viable offspring.

Therefore, the division into types, based only on physiological sign, erroneously.

Geographic criterion of the species

The geographical criterion is based on the allocation of distribution sites for individuals in certain territorial areas. But often the ranges of different species overlap or break, which calls into question the absolute application of the method.

Behavioral criterion of species

Behavioral or ethological criterion characterizes interspecies differences in the behavior of individuals.

Bird songs or sounds made by insects are used to recognize certain types animals. An important role is played by behavior during mating, reproduction and the nature of care for offspring.

View criteria - table for biology lessons with examples

Morphological features of representatives of flora and fauna

common wolf

The wolf genus consists of seven species and 17 subspecies belonging to the common or gray wolf (Canis lupus). The division into subspecies groups occurred due to different body proportions and hair color.

Morphological features:

• large sizes;
• external resemblance to a dog, differences in a more sloping frontal part, elongated paws, a lowered back part of the body, a straight tail and a special structure of the hairline;
• dark gray stripe along the ridge, crown of the head with dark markings, characteristic "mask" on the muzzle;
• the color is gray-brown, ocher-rusty and fawn, the roots and tips of the hair are dark, the middle is light tones.

The geography of habitat differs in the breadth of ranges. Exists in flocks from 2 to 40 animals. Differs in high social development. They make various sounds that facilitate communication between individuals.

The wolf belongs to typical predators, but plant foods are also present in the diet.

The wolf is a monogamous animal that lives in pairs from mating to maturation of the offspring. Mating games last from January to March. Sexual maturity in males occurs from 2 to 3 years, in females - by 2 years.

Cactus

The numerous cactus family has approximately 2800 species and is divided into 3 subfamilies:

1. Peyresky cacti include deciduous representatives;
2. Opuntias consist of flat cacti and are divided into 3 groups according to their shape;
3. Cereus include plants lacking leaves and glochidia.

Distinctive morphological features:

• the presence of an areola, represented by spines or hairs;
• the unique structure of the fruit and flower, which is the tissue of the stem.

Cactus are native to North and South America.

Amur tiger

The Amur tiger differs from other tigers in geographical and morphological features. The area is the Far East and the northern part of China.

External differences include:

• thick and long fur;
• fewer lanes.

What type criterion is the most accurate

The most clear boundaries between species groups can be determined using the genetic method.

But in nature, complete genetic isolation cannot exist, therefore, to identify the belonging of an organism to a certain species category, several different criteria must be used.

The most ancient species criterion

The oldest and most widespread method of describing new species is the morphological criterion, which systematizes individuals according to external similarity.

This method is also the least accurate due to the frequent significant difference between organisms of a certain species and the morphological similarity of various individuals.

Conclusion

Species criteria contribute to a deep study, analysis and the most accurate systematization of organisms. There are more than a million described species on Earth. a large number of still unknown and unexplored.

The study of species features contributes to understanding the process of evolution on Earth.

Goals: to form the concepts of "type" and "type criteria"; showmechanisms of reproductive isolation in nature; continue the formation of skills to give a morphological description of plants, work with texts, compile tables, analyze, formulate conclusions.

Equipment: paintings on zoology: "Hare-hare”, “Hare hare”, “Brown bear”, “White bear”; distributingexact material "Hare hare and hare-hare", "Raven and crow".

During the classes

I.Organizing time

The teacher announces the topic and objectives of the lesson.

11. Updating knowledge

1. Completion of tasks (orally).

Task number 1

Name the types of plants and animals you know that live near your home or school.

Task number 2

The teacher shows the picture Brown bear and ask questions:

The name of this species of animal is Brown Bear. Which of thesetwo words refers to the generic name, what - to the specific?

Name another species of animal from the same genus. (This is a bear white).

The teacher puts up a picture illustrating polar bear, next to the painting "Brown Bear".

Compare two species of the same genus. Show similarities and differences.

Task number 3,

In the specified list of animals, count the number of individuals, species and genera.

1. Hedgehog ordinary.

2. Common fox.

3. Himalayan or white-breasted bear.

4. Djungarian hamster.

5. White hare.

6. Brown bear.

7. Hamster Syrian or golden.

8. Hare-hare.

9. Eared hedgehog.

10. The fox is ordinary.

(Answer:number of individuals - 10; species - 9; childbirth - 5 (Hedgehog, Lisi-tsa, Bear, Hamster, Hare).)

By doing last job a number of students have a problem: to attribute the white hare and the brown hare to the same species or totwo different types. Is it true or false that the hareis a white hare a hare in winter?

Report "Hare hare and hare hare".

- What conclusion can be drawn from the results of all assignments to update knowledge?

Conclusion:

1. To designate a species, a double (binary) butmenclature, according to which the genus to whichrefers to the species (noun), and then the species name (adj. dumbbell).

2. Individuals of different species differ from each other in placestania, outward signs and etc.

3. Similar species are combined into one genus.

4. Species is the main category of biological classification.

III . Learning new material

1. Teacher's story.

- What is a species and what are its criteria?

IN Questioning about species and species criteria is central to the theory of evolution and has been the subject of numerous studies.research in the field of systematics, zoology, botany and otherSciences. And this is understandable: a clear understanding of the essencespecies is necessary to elucidate the mechanisms of evolutionary process.

A strict generally accepted definition of the species has not yet been developed.nerd. In biological encyclopedic dictionary we are onwe go to the following definition of the form:

“A species is a set of populations of individuals capable of interbreedingwith the formation of fertile offspring inhabiting a certainarea, which have a number of common morphophysiological features remote from other similar groups of individuals in practiceby the complete absence of hybrid forms.

Compare this definition with the one in your textbook.(textbook by A.A. Kamensky, § 4.1, p. 134).

Let us explain the concepts that occur. in the view definition:

area- area of ​​distribution of a given species or population in nature.

population(from lat. “Pop uius "- people, population) - totalthe number of individuals of the same species with a common gene pool and occupationcovering a certain territory - an area.

gene pool- the totality of genes that individuals haveof this population.

Consider the history of the development of views on the species in biology.

The concept of species was first introduced into science by an English botanist John Ray inXVII century. Foundational work on the species problemwas written by a Swedish naturalist and naturalistCarl Linnaeus in XVIII centuryin which he proposed the firstscientific definition of the species, clarified its criteria.

Teacher's comments. K. Linnaeus believed that the species is a unigreasy, really existing unit of living matter, morphologically homogeneous and unchanging . All individuals of the species, according to the scientist, have a typical morphological appearance, and variations are random deviations. , the result of an imperfect implementation of the idea of ​​the form (a kind of deformity). Scientistbelieved that species are unchanging, nature is unchanging. The idea is unchangedof nature rested on the concept of creationism, according towhich all things were created by God. Applied to biologyLinnaeus expressed this concept in his famous formulamule "There are as many species as different forms first produced the Infinite creature".

Another concept belongs Tom Baptiste Lamarck- ledto whom the French naturalist. According to his concept, the views are real Not exist, is a purely speculative concept invented forin order to make it easier to consider a larger number ofindividuals, because, according to Lamarck, “in nature there is noanything but individuals. Individual variability is continuous, therefore, the boundary between species can be drawn here and there - where it is more convenient.

The third concept was prepared in the first quarter XIX century. She was justified Charles Darwin and subsequent biologistmi. According to this concept, species have an independent reality. Viewheterogeneous, is a system of subordinate units. WITHAmong them, the basic elementary unit is the population. Species, by Darwin, change, they are relatively constant and areultatum of evolutionary development .

Thus, the concept of "species" has a long history of formation in biological science.

Sometimes the most experienced biologists are at a dead end, determiningwhether these individuals belong to the same species or not . Why is that happens, are there precise and strict criteria thatcould resolve all doubts?

Species criteria are traits by which one species differs.comes from another. They are also isolation mechanisms.interbreeding, independence, independently hundreds of species.

We know that one of the main features of biological matter on our planet is discreteness. It's in expressed in the fact that it is represented by separate species, notinterbreeding with each other, isolated from each other gogo.

The existence of a species is ensured by its genetic unity.(individuals of the species are able to interbreed and produce viable fertile offspring) and its genetic independence (impossiblethe possibility of interbreeding with individuals of another species, not viablestability or sterility of hybrids).

The genetic independence of the species is determined by the totalits characteristic features: morphological, physiological, biochemical, genetic, lifestyle, behavior, geographical distribution, etc. This is Crete eriivid.

Let's get to know them.

2. Work in groups

Each group receives a text illustrating one of the view criteria. After 5 minutes, you need to talk about the essence of this criterion and what is the disadvantage of this criterion. As the groups perform, the class fills in the table “View criteria”.

Table No. 1

View criteria.

So, the species criteria by which we distinguish one species from another, together determine the genetic isolation of the species.dov, ensuring the independence of each species and diversityin nature. In fact, in the development of these isolating species recognitionkov and is the process of formation of species. That is whythe study of species criteria is of decisive importance forunderstanding the mechanisms of the evolutionary process taking place on our planet.

3. Formulation of conclusions.

After filling in the table, conclusions are formulated:

1) Species criteria by which one species differs from anotherth, together they determine the genetic isolation of species, ensuring the independence of each species and their diversity in nature.

2) There is not a single species criterion that could berecognized as absolute and universal.

3) To methods of isolation that prevent the crossing of different species include:

A) differences in areas, habitats => impossibility of meeting;

b) different dates breeding;

V) differences in the structure of the genital organs;

G) non-viability or sterility of hybrids;

e) different rituals of "courtship" during the breeding season.

4) A species is genetically relatively isolated bathroom system, which proves the reality of the existence of species in nature.

Remember what was said in the text “A white hare and a harehare". What type criteria are used to describe the tsev?

Answer the question:

- What species criteria are used in the description of animals?

1). The mute swan often bends S-shaped neck , and the beak and head are held obliquely to the water. At timesdredging makes a characteristic hissing sound, according to which he receivedits name. The mute swan is common in isolated areasin the middle and southern strip of Europe and Asia from southern Sweden, Denmark andPoland in the west to Mongolia, Primorsky Krai and China in the East.Everywhere in this territory it is rare, often a pair from a pair nests on the groat a great distance, and in many areas it is completely absent.Inhabits estuaries overgrown with aquatic vegetation, lakes, sometimeseven swamps, preferring the deaf, little visited by man.

The small or tundra swan is distributed throughout the tundraasian off Kola Peninsula in the west to the Kolyma delta in the East,entering the forest-tundra region and the western islands of the Arctic. For nestingselects swampy and low grassy areaslakes scattered over them, as well as river valleys aboundingoxbows and channels.

Mating games are peculiar and take place on land. At the same time, the male walks in front of the female, stretches his neck, sometimes raises his wings,making a special clapping sound with them and screaming loudly.

2). Go native martin. topcatches, back, wings and tailblue-black, rump and all underpartswhite. Tail with sharp triangularnotch at the end. dwellermountain and cultural landscapes.It nests on the walls of rocks and buildings. P erelet bird. Keeps in packsin the air or sitting on wires, more often than other swallows sits on zearth. Breeds in colonies. The nest is molded from lumps of clay in the formhemisphere with side entrance. Clutch of 4-6 white eggs in May - June. Goal os - voiced "tirrch-tirrch"

Coast swallow. The top of the head, neck, back, wings, tail and stripe across the chest are grayish-brown, the throat, chest and abdomen are white. Tail with a shallow notch.

Inhabits river valleys, where it nests on steep clay or sandy banks. Common or numerous migratory bird. Lives in flocks, nests in colonies. Nests are arranged in burrows along steep river banks. Clutch of 4-6 white eggs in May-July. Voice - low "chirr- chirr

Homework

According to the textbook A.A. Kamensky, § 4.1, questions after the paragraph, terms.

Individually:

1) The message "Is it true that the raven is the husband of the crow?"

2 ) Using literary sources, give specific examplesMeasures of geographical, ecological and ethological criteria.

Supplementary material for group work.

View criteria

Morphological criterion

It was the first and for a long time the only criterion used to describe species.

Morphological criterion is the most convenient and noticeable, thereforeand is now widely used in the taxonomy of plants and animals.

We can easily distinguish by the size and color of the plumage of a largespotted woodpecker from green woodpecker, lesser spotted woodpecker and yellow(black woodpecker), great tit from crested, long-tailed, blueand chickadees, meadow clover from creeping and lupine, etc.

Despite the convenience, this criterion does not always “work”. You can’t use it to distinguish between twin species, practicallymorphologically different. There are many such species among malarialmosquitoes, fruit flies, whitefish. Even birds have 5% of twin species, andThere are 17 of them in one row of North American crickets.

The use of morphological criteria alone canlead to erroneous conclusions. So, K. Linnaeus in particularexternal structure classified male and female mallard ducks as different species. Siberian hunters identified five variations based on the color of fox fur: gray foxes, moths, crosses, black-brown and black. In England, 70 species of butterflies, along with individuals with a light color, also have themes.nye morphs, the number of which in populations began to increase inconnection with forest pollution. Polymorphism - widespreadphenomenon. It occurs in all species. It also affects those features by which species differ. In lumberjack beetles, for example, in barbeled flowersexact, found in late spring on a bathing suit, in addition to tiIn the peak form, up to 100 color aberrations occur in populations. In the days of Linnaeus, the morphological criterion was the main one, sincewaist that there is one typical form for the species.

Now that it is established that a species can have many forms, such asthe logical concept of species is discarded and the morphological criterion is notalways satisfies scientists. However, it must be recognized that this criterionis very convenient for systematizing species, and in most determinants of animals and plants it plays a major role.

Physiological criterion

Physiological features of various types of plants and bellynyh are often a factor that ensures their genetic selfvalue. For example, in many fruit flies, the sperm of individuals of a foreign speciesYes, it causes an immunological reaction in the female genital tract, which leads to the death of spermatozoa. Hybridization of various species andsubspecies of goats often leads to a violation of the periodicity of the fetuswearing - the offspring appears in winter, which leads to his death. Crossbreedsthe study of different subspecies of roe deer, for example, Siberian and European,sometimes leads to the death of females and offspring due to large size fetus.

Biochemical criterion

Interest in this criterion has emerged in recent decades in connection withdevelopment of biochemical research. It is not widely used, since there are no specific substances characteristiconly for one species and, in addition, it is very laborious and far not universal. However, they can be used in cases wherewhen other criteria do not work. For example, for two twin speciesbutterflies from the genus Amata (A. p h e g ea and A. g ugazzii ) diagnosticand signs are two enzymes - phosphoglucomutase and esterase-5, allowing even identify hybrids of these two species. IN Lately widely used comparative study of the composition of DNK in practical taxonomy of microbes. The study of the composition of DNA allowed to revise the phylogenetic system of various groups microorganisms. The developed methods make it possible to compare the compositionDNA in bacteria preserved in the depths of the earth and now livingforms. For example, a comparison was made of the composition of DNA in a lyingabout 200 million years in the thickness of salts of the Paleozoic bacterium pseudosalt-loving monads and in living pseudomonads. The composition of their DNA turned out to be identical, and biochemical properties - similar.

Cytological criterion

The development of cytological methods has allowed scientists to investigate theRmu and the number of chromosomes in many species of animals and plants. A new direction has appeared - karyosystematics, which has introduced somecorrections and clarifications to the phylogenetic system built on the basis of morphological criteria. In some cases, the number of chromosomes serves characteristic feature kind. Karyological analysis allowed, for example, to streamline the taxonomy of wild mountain sheep, whichry different researchers identified from 1 to 17 species. The analysis showedthe presence of three karyotypes: 54 chromosome - in mouflons, 56rhomosomal - in argali and argali and 58-chromosome - in inhabitantsmountains of Central Asia - urials.

However, this criterion is not universal. First, atmany different species have the same number of chromosomes and their shape is similar. Secondly, individuals with different numbers of chromosomes may occur within the same species. These are the so-called chromosomal and genomicpolymorphism. For example, goat willow has a diploid - 38 and a tetraploid the new number of chromosomes is 76. In silver carp, there are populations with a setrum chromosomes 100, 150, 200, while their normal number is 50. In the rainbow trout, the number of chromosomes varies from 58 to 64, in the White Seadi meet individuals with 52 and 54 chromosomes. In Tajikistan on the siteonly 150 km long, zoologists discovered a population of mole voles with a set of chromosomes from 31 to 54. In gerbils from different places habitats, the number of chromosomes is different: 40 - in Algerian gerbils skian populations, 52 - in Israeli and 66 - in Egyptian. To infusion current time, intraspecific chromosomal polymorphism was found in 5% of ctotal genetically studied species of mammals.

Sometimes this criterion is incorrectly interpreted as genetic. Undoubtedly, the number and shape of chromosomes is an important feature that prevents crossbreedingof individuals of different species. However, this is rather a cytomorphologicalcue criterion, since we are talking about intracellular morphology: the numberand the shape of chromosomes, and not about the set and structure of genes.

E tological criterion

For some animal species, a mechanism that preventsbaptism and leveling the differences between them are especiallybennosti their behavior, especially during the mating season. Partner recognition own species and rejection of courtship attempts by males of another speciesbased on specific stimuli - visual, soundchemical, tactile, mechanical, etc.

In the widespread genus warblers, different species are very similarlive on top of each other morphologically, in nature they cannot be distinguished either by color or by size. But they all differ very well in song and by habits. The song of the willow warbler is complex, similar to the song of the chaffinch, only without his final knee, and the song of the chiffchaff is aboutstenky monotonous whistles. Numerous twin species of ameRican fireflies of the genus P hotinus were first identified bydifferences in their light signals. Male fireflies in flight flashes of light, the frequency, duration and alternation of whichspecific to each species. well known but that a number of species of orthoptera and homopterans living within,of the same biotope and breeding synchronously, differ onlythe nature of their calling signals. Such double species with acousticreproductive isolation are found, for example, in crickets, skating fillies, cicadas and other insects. Two closely related species of Americanfrogs also interbreed because of differences in the call of males.

Differences in demonstrative behavior often play a decisive role in reproductive isolation. For example, related species of Drosophila flies fromdiffer in the specifics of the ritual of courtship (according to the nature of the vibrationwings, leg trembling, whirling, tactile contacts). Two closespecies - the herring gull and the klusha have differences in the degree of pronouncedhundreds of demonstrative poses, and seven species of lizards of the genus S se1horns s differ in the degree of raising the head when courting sexual partners.

Environmental criterion

Behavioral features are sometimes closely related to the ecological specifics of the species, for example, to the peculiarities of nest construction. Three species of our common tits nest in hollows deciduous trees, predominantly birches. great tit in the Urals chooses usually deep a hollow in the lower part of a birch or alder trunk, formed in a re as a result of rotting of the knot and adjacent wood. This hollow is inaccessible to woodpeckers, crows, or predatory mammal. Tit moskovka populates frost cracks in the trunks of birch and alder. Hathe egg prefers to build a hollow itself, plucking cavities into rottenor old birch and alder trunks, and without this time-consuming procedure, she will not lay eggs.

Features of the lifestyle inherent in each species determineits position, its role in the biogeocenosis, that is, its ecologicalniche. Even the closest species, as a rule, occupy different econiches, that is, they differ in at least one or two ecological signs.

Thus, the econiches of all our species of woodpeckers differ in the nature of their diet. Great spotted woodpecker feeds on larch seeds in winter tsy and pines, crushing cones in their "forges". black woodpeckerzhelna extracts barbel larvae and gold beetles from under the bark and from woodfir, and the small spotted woodpecker hammers soft alder wood or extracts nase lumps from the stems of herbaceous plants.

Each of the 14 species of Darwin's finches (named afterC. Darwin, who first paid attention to them), living on the Galapagos islands, has its own specific eco-niche, which differs from others primarily in the nature of food and ways of obtaining it.

Neither the ecological nor the ethological crite discussed aboverii are not universal. Very often individuals of the same species, but oncepopulations differ in a number of lifestyle featuresand behaviour. And vice versa, different species, even very distant ones, in the systemchemically, may have similar ethological characteristicsor play the same role in the community (for example, the role of a herbivorous mammal and insects, say, such as locusts, are quite comparable).

Geographic criterion

This criterion, along with the ecological one, takes the second (after the morphological) place in most determinants. When determining many species of plants, insects, birds, mammals and othergroups of organisms whose distribution is well studiedThe distribution of the range plays a significant role. In subspecies, the ranges, as a rule, do not coincide, which ensures their reproductive isolation and, in fact,, their existence as independent subspecies. many kindsoccupy different ranges (such species are called allopatric And). But a vast number of species have overlapping or overlappingexpanding ranges (sympatric species). In addition, there are typeshaving clear boundaries of distribution, as well as braid speciesmopolitans living on vast expanses of land or ocean. INdue to these circumstances, the geographical criterion cannot be universal.

Genetic criterion

Genetic unity of the species and, accordingly, genetic isolationit from other species - main criterion species, main speciesa sign due to a complex of features of the structure and lifeactivities of organisms of this species. Genetic compatibilitybridge, similarity of morphological, physiological, cytologicaland other signs, the same behavior, living together - all thiso creates the necessary conditions for successful reproduction andspecies production. At the same time, all these traits provide geneticisolation of a species from other similar species. For example, oncelychia in the song of thrushes, warblers, warblers, finches and finches, deafand common cuckoo prevent the formation of mixed pairs,despite the similarity of their coloration and ecology (hybrids are almost never found in birds with a specific song). Even in those cases I, when, despite isolation barriers, interbreeding occurredthe formation of individuals of different species, a hybrid population, as a rule, does not arise, since a number of post-populationisolation mechanisms. The most important of them is the death of male gametes (genetical incompatibility), death of zygotes, non-viability of thereeds, their sterility, finally, the inability to find a sexualpartner and produce viable fertile offspring. We know thatEach species has its own set of specific features. An interspecific hybrid will have characters intermediate betweenfeatures of the two original parental forms. His song, for example will not be understood by either a chaffinch or a finch if it is a hybrid of these species, and he will not find a sexual partner. In such a hybrid,the formation of gametes, the finch chromosomes contained in its cells “do notfind the chromosomes of the finch and, not finding a homologous partner, do notconjugate. As a result, gametes with a disturbed set are formed.chromosomes, which are usually not viable. And as a resultThis hybrid will be sterile.

Raven and crow

I will say right away: Raven is not the "husband" of the crow, but an independent species.

The raven is one of the largest members of the crow family., weighs from 0.8 to 1.5 kg. The color of the plumage, beak and legs is monophonic black color.

The raven is distributed almost throughout the northern hemisphere: it occursalmost throughout Europe, Asia, excluding Southeast, in NorthAfrica and North America. Everywhere he leads a settled way of life. Inhabits forests, deserts and mountains. In treeless areas keeps atrocks, coastal cliffs of river valleys. Mating and mating gamesin the south of the country are celebrated in the first half of February, in the north - inMarch. Couples are constant. Nests are usually placed on the tops of tall trees. In clutch from 3 to 7, more often 4-6, eggs are bluish-green in color. ki with dark markings.

Raven is an omnivorous bird. His main food is carrion, which he oftenfinds everything in landfills and slaughterhouses. Eating carrion, he performslike a sanitary bird. It also feeds on rodents, eggs,and chicks, fish, various invertebrates, and placesmi and grains of cereals.

The crow in general physique resembles a crow, but significantlysmaller than it: weighs from 460 to 690 g.

The described species is interesting in that, according to the color of the plumage, it breaks upinto two groups: gray and black. The hooded crow is well knownnew two-tone color: head, throat, wings, tail, beak and legs are black, the rest of the plumage is gray. Black Crow is all black, with a metallic blue and purple sheen.

Each of these groups has a local distribution. The gray crow is widespread in Europe, Western Asia, the black one is in Central and Western Europe, on the one hand, in Central, East Asia and North America on the other.

The crow inhabits the edges and outskirts of forests, gardens, groves, thickets of river valleys, less often rocks and slopes of coastal cliffs. It is partly sedentary, partly migratory bird.

In early March, in the southern parts of the country and in April-May in the northern and eastern parts, egg laying begins. The clutch usually contains 4-5 pale green, bluish-green or partially green eggs with dark spots and speckles. The crow is an omnivorous bird. From animals, she eats various invertebrates - beetles, ants, mollusks, as well as rodents, lizards, frogs and fish. From plants, it pecks grains of cultivated cereals, seeds of spruce, field bindweed, bird buckwheat, etc. In winter, it feeds mainly on garbage.

White Hare and European Hare

The genus of hares proper, which includes the hare and hare, as well as another 28 species , quite numerous. The most famous hares in Russia are hare and hare. White hare can be found on the territory from the coast of the Arctic Ocean to the southern border of the forest zone, in Siberia - to the borders with Kazakhstannom, China and Mongolia, and on Far East- from Chukotka to and North Korea. The hare is also common in the forests of Europe, as well as in the east of Northern America. Rusak lives in the territory European Russia from Kareliasouth of the Arkhangelsk region to the southern borders of the country, in Ukraine and in the Zakavcasier. But in Siberia, this hare lives only in the south and west of Lake Baikal.

Belyak got its name due to snow-white winter fur. Only the tips of his ears remain black all year round. Rusak, in some northern areas, also brightens greatly by winter, but it never happens to be snow-white. And in the south it does not change color at all.

The hare is more adapted to life in open landscapes, since it is larger than the white hare, and it runs better. At short distances, this hare can developspeed up to 50 km/h. The hare's paws are wide, with dense pubescence to fall less into loose forest drifts. And the hare already has paws, because on open places snow, as a rule, is hard, packed, "trodden down by the wind."

The body length of the hare is 45-75 cm, weight is 2.5-5.5 kg. The ears are shorter than those of the hare. The body length of a hare is 50-70 cm, weight is up to 5 (sometimes 7) kg.

breed hares usually two, and in the south three or even four times a year. Wu harebelyakovs in the output can be two, three five, seven hares, and the hare- usually only one or two hares. Rusaks begin to taste grass two weeks after birth, and whites even faster - a week later.

The genetic (cytogenetic) species criterion, along with others, is used to distinguish between elementary systematic groups, analysis of the state of the view. In this article, we will consider the characteristics of the criterion, as well as the difficulties that a researcher using it may face.

In different industries biological science type is defined differently. From an evolutionary perspective, we can say that a species is a collection of individuals that have a similarity in external structure and internal organization, physiological and biochemical processes capable of unlimited interbreeding, leaving fertile offspring and genetically isolated from similar groups.

A species can be represented by one or several populations and, accordingly, have a whole or dissected range (habitat area / water area)

Species nomenclature

Each type has its own name. In accordance with the rules of binary nomenclature, it consists of two words: a noun and an adjective. The noun is the generic name, and the adjective is the specific name. For example, in the name "Dandelion officinalis", the species "officinalis" is one of the representatives of plants of the genus "Dandelion".

Individuals of related species within the genus have some differences in appearance, physiology, and ecological preferences. But if they are too similar, then their species affiliation is determined by the genetic criterion of the species based on the analysis of karyotypes.

Why does a species need criteria?

Carl Linnaeus, who was the first to give modern names and describe many types of living organisms, considered them unchanged and non-variable. That is, all individuals correspond to a single species image, and any deviations from it are a mistake in the embodiment of the species idea.

Since the first half of the 19th century, Charles Darwin and his followers have been substantiating a completely different concept of the species. In accordance with it, the species is changeable, heterogeneous and includes transitional forms. The constancy of the species is relative, it depends on the variability of conditions environment. The elementary unit of existence of a species is a population. It is reproductively isolated and corresponds to the genetic criterion of the species.

Given the heterogeneity of individuals of the same species, it can be difficult for scientists to determine the species affiliation of organisms or distribute them between systematic groups.

Morphological and genetic criteria of a species, biochemical, physiological, geographical, ecological, behavioral (ethological) - all these are complexes of differences between species. They determine the isolation of systematic groups, their reproductive discreteness. And by them it is possible to distinguish one species from another, to establish the degree of their relationship and position in the biological system.

Characteristics of the genetic criterion of the species

The essence of this trait is that all individuals of the same species have the same karyotype.

A karyotype is a kind of chromosomal "passport" of an organism, it is determined by the number of chromosomes present in mature somatic cells of the body, their size and structural features:

• the ratio of the length of the arms of the chromosomes;
• the position of the centromeres in them;
• the presence of secondary constrictions and satellites.

Individuals belonging to different species will not be able to interbreed. Even if it is possible to produce offspring, as with a donkey and a horse, a tiger and a lion, then interspecific hybrids will not be prolific. This is due to the fact that the halves of the genotype are not the same and conjugation between chromosomes cannot occur, so gametes are not formed.

In the photo: a mule is a sterile hybrid of a donkey and a mare.

Object of study - karyotype

The human karyotype is represented by 46 chromosomes. In most species studied, the number of individual DNA molecules in the nucleus that form chromosomes falls within the range of 12–50. But there are exceptions. The fruit fly Drosophila has 8 chromosomes in the cell nuclei, and the small representative of the Lepidoptera family Lysandra has a diploid chromosome set of 380.

An electron micrograph of condensed chromosomes, which allows one to assess their shape and size, reflects the karyotype. Karyotype analysis within the study genetic criterion, as well as comparing karyotypes with each other helps to determine the species of organisms.

When two kinds are one

The common feature of view criteria is that they are not absolute. This means that the use of only one of them may not be sufficient for an accurate determination. Organisms that are outwardly indistinguishable from each other may be representatives of different species. Here the morphological criterion comes to the aid of the genetic criterion. Twin examples:

1. To date, two species of black rats are known, which were previously defined as one due to their external identity.
2. There are at least 15 types malarial mosquitoes, which are distinguishable only through cytogenetic analysis.
3. In North America, 17 species of crickets were found that have genetic differences, but are phenotypically related to a single species.
4. It is believed that among all species of birds there are 5% of twins, for the identification of which it is necessary to apply a genetic criterion.
5. The confusion in the taxonomy of mountain bovids was eliminated thanks to karyological analysis. Three varieties of karyotypes have been identified (2n=54 in mouflons, 56 in argali and argali, and 58 chromosomes in urials).

One of the species of black rats has 42 chromosomes, the karyotype of the other is represented by 38 DNA molecules.

When one view is like two

For species groups with a large area of ​​​​the range and the number of individuals, when geographical isolation operates within them or individuals have a wide ecological valence, the presence of individuals with different karyotypes is typical. Such a phenomenon is another variant of exceptions in the genetic criterion of a species.

Examples of chromosomal and genomic polymorphism are common in fish:

• in rainbow trout, the number of chromosomes varies from 58 to 64;
• two karyomorphs, with 52 and 54 chromosomes, were found in the White Sea herring;
• with a diploid set of 50 chromosomes, representatives of different populations of silver carp have 100 (tetraploids), 150 (hexaploids), 200 (octaploids) chromosomes.

Polyploid forms are found in both plants (goat willow) and insects (weevils). House mice and gerbils may have a different number of chromosomes that is not a multiple of the diploid set.

Twins by karyotype

Representatives of different classes and types may have karyotypes with the same number of chromosomes. There are much more such coincidences among representatives of the same families and genera:

1. Gorillas, orangutans, and chimpanzees have a 48-chromosome karyotype. In appearance, the differences are not determined, here you need to compare the order of nucleotides.
2. There are insignificant differences in the karyotypes of the North American bison and the European bison. Both have 60 chromosomes in a diploid set. They will be assigned to the same species if the analysis is carried out only by genetic criteria.
3. Examples of genetic twins are also found among plants, especially within families. Among willows, it is even possible to obtain interspecific hybrids.

To identify subtle differences in the genetic material in such species, it is necessary to determine the sequences of genes and the order in which they are included.

The influence of mutations on the analysis of the criterion

The number of karyotype chromosomes can be changed as a result of genomic mutations - aneuploidy or euploidy.

With aneuploidy, one or more additional chromosomes appear in the karyotype, and there may also be a smaller number of chromosomes than in a full-fledged individual. The reason for this violation is the non-disjunction of chromosomes at the stage of gamete formation.

The figure shows an example of aneuploidy in humans (Down syndrome).

Zygotes with a reduced number of chromosomes, as a rule, do not proceed to cleavage. And polysomic organisms (with "extra" chromosomes) may well be viable. In the case of trisomy (2n+1) or pentasomy (2n+3), an odd number of chromosomes will indicate an anomaly. Tetrasomy (2n + 2) can lead to an actual error in determining the species by genetic criteria.

Multiplication of the karyotype - polyploidy - can also mislead the researcher when the mutant karyotype is the sum of several diploid sets of chromosomes.

Complexity of the criterion: elusive DNA

The uncoiled DNA strand diameter is 2 nm. The genetic criterion determines the karyotype in the period preceding cell division, when thin DNA molecules repeatedly spiralize (condense) and represent dense rod-shaped structures - chromosomes. Chromosome thickness is on average 700 nm.

School and university laboratories are usually equipped with microscopes with a low magnification (from 8 to 100), it is not possible to see the details of the karyotype in them. The resolving power of a light microscope, in addition, allows at any, even the highest magnification, to see objects not less than half the length of the shortest light wave. Waves have the shortest length purple(400 nm). This means that the smallest object visible in a light microscope will be from 200 nm.

It turns out that the stained decondensed chromatin will look like cloudy areas, and the chromosomes will be visible without details. An electron microscope with a resolution of 0.5 nm allows you to clearly see and compare different karyotypes. Considering the thickness of filamentous DNA (2 nm), it will be clearly distinguishable under such a device.

Cytogenetic criterion at school

For the reasons described above, the use of slides on laboratory work according to the genetic criterion of the species is impractical. In tasks, you can use photographs of chromosomes obtained under an electron microscope. For the convenience of working in the photo, individual chromosomes are combined into homologous pairs and arranged in order. Such a scheme is called a karyogram.

Sample assignment for laboratory work

Exercise. Consider the given photographs of karyotypes, compare them and conclude that individuals belong to one or two species.

Photographs of karyotypes for comparison in laboratory work.

Working on a task. count up total chromosomes on each karyotype photo. If they match, compare them appearance. If not a karyogram is presented, find the shortest and longest among the chromosomes of medium length in both images, compare them according to the size and location of the centromeres. Make a conclusion about the difference / similarity of karyotypes.

Answers to the task:

1. If the number, size and shape of the chromosomes match, then the two individuals whose genetic material is presented for study belong to the same species.
2. If the number of chromosomes differs by a factor of two, and chromosomes of the same size and shape are found in both photographs, then most likely the individuals are representatives of the same species. These will be diploid and tetraploid karyotypes.
3. If the number of chromosomes is not the same (it differs by one or two), but in general the shape and size of the chromosomes of both karyotypes are the same, we are talking about normal and mutant forms of the same species (the phenomenon of aneuploidy).
4. With a different number of chromosomes, as well as a mismatch in the characteristics of size and shape, the criterion will classify the presented individuals as two different species.

In the conclusion, it is required to indicate whether it is possible to determine the species affiliation of individuals based on the genetic criterion (and only it).

Answer: it is impossible, since any species criterion, including genetic, has exceptions and can give an erroneous result of the determination. Accuracy can only be guaranteed by the use of a set of type criteria.