Question 1. What is a species?

A biological species is a set of individuals that have the ability to interbreed with the formation of fertile offspring; inhabiting a certain area; possessing a number of common morphological and physiological characteristics and similarities in relationships with the biotic and abiotic environment.

Question 2. Which biological mechanisms prevent the interbreeding of individuals different types?

The isolation of a species is maintained by reproductive isolation, which prevents it from mixing with other species during reproduction. Isolation is ensured by differences in the structure of the genital organs, fragmentation of habitats, differences in timing or places of reproduction, differences in behavior, ecological isolation and other mechanisms.

Geographical isolation. Species that live at great distances or are separated by an insurmountable barrier are not able to exchange genetic information.

Seasonal isolation. The difference in breeding seasons for different species is ensured. For example, in one species of California pine, pollen ripens in February, and in another, in April.

Behavioral isolation. Characteristic of higher animals. For example, in many closely related species of waterfowl, mating behavior has its own characteristics, which eliminates the possibility of interspecific crossing.

Question 3. What is the reason for the infertility of interspecific hybrids?

Every separate species has its own karyotype, which differs in the number of chromosomes, their shape, size, and structure. Differences in karyotypes lead to impaired fertilization, the death of embryos or the birth of infertile offspring. The sterility of the offspring is due to the fact that in the absence of paired homologous chromosomes, conjugation is disrupted in prophase I of meiosis. As a result, bivalents are not formed, meiosis is disrupted, and the development of full-fledged gametes does not occur in the hybrid offspring.

Question 4. Define the concept of “species range”.

The range of a species is the area of ​​distribution of the species. The size of their habitats can vary greatly among different species. For example, Scots pine grows almost throughout the entire territory of Russia, and snowdrop is characteristic only of the North Caucasus.

Question 5. What is the radius of individual activity of organisms? Estimate the range of individual activity of some animal species typical of your region.

The radius of individual activity is the distance over which an organism can move, based on its vital characteristics and physical capabilities.

Activity of organisms: 1) in plants - the rate of horizontal growth of rhizomes and plagiotropic shoots (per year), as well as the distances over which diaspores and pollen are dispersed in one way or another; 2) in animals - the form of their behavior: the duration of active activity, taking into account the distances (radii of activity) of movement in individual habitats, as well as migration.

Question 6. What is a population? Do you think the range of a population can coincide with the range of a species? Prove your opinion.

A population is a collection of individuals of the same species, inhabiting a certain territory for a long time, freely interbreeding with each other and partially or completely isolated from individuals of other similar populations.

The species' range is usually home to a fairly significant number of populations, each of which is an elementary unit of evolution.

Question 7. How are the boundaries of a species’ habitat determined?

There is a division of boundaries into climatic, landscape, and biocenotic ones. They can be called environmental boundaries, since they are determined by a combination of factors. On the other hand, there are many cases where the border remains stable and dispersal does not occur, despite the fact that environmental conditions inside and outside the range are homogeneous and quite favorable for the species.

Biocenotic boundaries are determined by the relationships of different species in a community.

Range boundaries are often determined by changes climatic conditions, especially hydrothermal regime, day length, snow cover thickness, etc. The essence of climatic boundaries varies; in some cases, the limit of distribution of a species is determined by a lack of heat or a reduction in the duration of the warm period; in others, the severity of winters or a decrease in the amount of precipitation during a certain part of the year may be decisive.

The boundaries of the range are determined by various factors, including vital role climatic, edaphic, biocenotic and anthropogenic factors play a role.

>> Isolating mechanisms

1. What is the reason for the difference between the organisms discovered by Charles Darwin on the Galapagos Islands and closely related forms on the mainland?
2. What natural factors isolate some populations organisms from other populations of the same species?

Darwin discovered that differences between populations of the same species manifest themselves in the form of adaptation to different conditions life. In the light of modern knowledge, this means that individuals in populations develop certain genetically fixed properties that distinguish them from each other and ensure the best adaptation of organisms to the conditions of a particular area. Here's an example. Atlantic herring populations in different ocean areas multiply V different time of the year. A necessary condition The survival of juvenile herring is due to the coincidence in the timing of the hatching of larvae from eggs and the development of small phytoplankton - their main food. Depending on the latitude of the area, the peak development of phytoplankton occurs in spring, summer, autumn or winter.

Accordingly, spring-, summer-, autumn- and winter-spawning herring are distinguished, the populations of which live separately, have slight external differences, but belong to the same species and can interbreed, producing fertile offspring.

Can differences between populations lead to their reproductive isolation, to the loss of the ability of individuals from different populations to freely interbreed with each other?

Populations living on different islands are isolated from each other, and their individuals practically do not mix. It is clear that under conditions of such purely geographical isolation, differences in structure or behavior gradually accumulate, and this may ultimately lead to the formation of new species of animals or plants.

How do individuals of different populations lose the ability to interbreed and exchange genes with other individuals of the same species? Is this simply due to geographical separation or are there other mechanisms? The answers to these questions provide the key to understanding the mechanisms of speciation.

It has been established that physical factors environment habitat and biological properties organisms can lead to restrictions on gene exchange. This occurs as a result of the activation of various types of isolating mechanisms

Let's look at some examples.

The Hawaiian Islands are home to two species of fruit flies that are very similar in appearance. Both species live in the same places, feeding on the sap of the same woody plant. In this case, one species feeds on sap flowing down the trunks and branches in the upper tiers of the tree, while the other feeds on puddles of sap on the forest floor. Crossing between these species never occurs due to their spatial separation. This example shows that genetic differences between populations can arise from different ecological specializations.

An interesting example of behavioral isolation is demonstrated by various species of fireflies. Each of the species living together is characterized by a certain light trajectory and types of emitted light signals. The trajectories can be zigzag, straight or in the shape of a loop, and the light pulsations can be short or long in the form of stable reflections (Fig. 76). When mating, individuals select each other, strictly focusing on the type of light signal. This example shows that isolation between populations can be consolidated by the formation of certain types of behavior - the development of reflex reactions only to signals of one type or another.

The pollen of some plant species, such as orchids, is carried only by certain species of animals, whose instinctive behavior ensures that gene exchange will occur only among individuals of their own species.

In animals with external fertilization, isolating mechanisms operate at the molecular level. In starfish and some species of mollusks, the role of insulating factors play differences in the structure of special protein molecules that connect sperm and eggs. Being on the surface of eggs, these molecules react only to sperm of “their” species, which excludes the possibility of fusion of reproductive products of different species. In animals with internal fertilization, this role is played by differences in the structure of the genital organs.

Finally, in many animals the breeding season begins under strictly defined combinations of external factors (for example, temperature and light). These factors act on them as signals to begin mating. Different species react to the same factors differently, which is why their breeding times do not coincide. Figure 77 shows the differences in breeding times among different species of amphibians living in the same areas .

Isolating mechanisms prevent the development of an organism from a zygote formed as a result of the fusion of gametes of a male and female of different species. Hybrids that arise in this way usually die quickly or remain infertile. For example, a mule - a hybrid of a horse and a donkey - is sterile; it cannot produce offspring due to the fact that meiosis is impossible with its set of chromosomes. Hybrids of the white hare and brown hare, marten and sable are sterile.

Reproductive isolation. Isolating mechanisms.

1. What are isolating mechanisms? What is the importance of isolating mechanisms?
2. What types of isolating mechanisms do you know? Give examples.
3. Why hybrids various types organisms are sterile?

Kamensky A. A., Kriksunov E. V., Pasechnik V. V. Biology 9th grade
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Textbook for grades 10-11

§ 49. Isolation - an evolutionary factor

Even C. Darwin pointed out that isolation is a very important evolutionary factor, since it leads to divergence in the characteristics of individuals within the same species and prevents the crossing of individuals of different species with each other.

Geographical isolation. Let us consider the ways in which isolation is carried out in nature, leading to divergence of characteristics in the population. The most common is spatial, or geographic, isolation. Its essence lies in the rupture of the single habitat in which the species lived into parts that do not communicate with each other. As a result, individual populations become isolated, so free crossing of individuals from different parts area is either impossible or extremely difficult.

Mutations can occur randomly in any isolated population. Due to genetic drift and action natural selection the genotypic composition of isolated populations becomes more and more different.

The reasons leading to the emergence of geographic isolation are numerous: the formation of mountains or rivers, isthmuses or straits, the extermination of populations in certain areas, etc.

Due to the impossibility of crossing individuals from different isolated populations, each of them develops its own direction of the evolutionary process. Over time, this leads to significant differences in their genotypic structure and a weakening and even complete cessation of gene exchange between populations.

Environmental insulation. Another way leading to population divergence is ecological isolation. It is based on differences in the preferences of animals or plants to settle in a certain place and interbreed at a strictly defined time of year. Some salmon fish, for example, do not spawn annually, but every other year. Moreover, one population of fish comes to spawn in the same spawning area in an even year, and another in an odd year. For this reason, representatives of different populations cannot interbreed and the populations become isolated.

Another type of ecological isolation is associated with the preference of living organisms for a particular habitat. Sevan trout is an example of such isolation. Different populations of trout spawn at the mouths of different streams and mountain rivers flowing into the lake, so free interbreeding between them is extremely difficult. Ecological isolation thus prevents the interbreeding of individuals from different populations and serves, like geographic isolation, to initial stage population divergences.

Biological mechanisms that prevent individuals of different species from interbreeding. There are complex mechanisms that prevent individuals of different species living in the same territory from interbreeding. Differences in animal behavior are especially important in implementing such isolation.

The dissimilarity in mating songs, courtship rituals, emitted odors, preferred habitats - all this reliably protects individuals of different species from mating. Many species, in addition, have differences in the structure of the genital organs, which is an additional obstacle to crossing. In plants, the inability of pollen of some species to germinate on the stigmas of other species is observed. In the event that fertilization does occur, the death of the zygotes is observed for genetic reasons. In cases where all barriers are overcome and hybrid offspring are nevertheless born, they are often infertile due to meiotic disorders due to differences in the structure and number of chromosomes.

So, Various types isolation, on the one hand, creates the prerequisites for the divergence of populations and subsequent speciation, and on the other hand, they contribute to the preservation of the genetic structure of the species.

1. Explain how new species form under conditions of geographic or environmental isolation.
2. What is the difference between geographic and environmental isolation?

§ 10- TYPE, ITS CRITERIA AND STRUCTURE

1) Formulate a definition of the concept “biological species”.

• Answer: A biological species is a collection of individuals that are similar in structure and have common origin, freely interbreeding and producing fertile offspring.

2) Define reproductive isolation and indicate its biological significance.

• Answer: Reproductive isolation is the existence of mechanisms that prevent the interbreeding of different species.
• Its biological significance is that it prevents the exchange of genes between species, which in combination gives natural conditions genetic isolation between species.

3) List the mechanisms that ensure genetic isolation of the species.

• Answer:
• 1- Reproduction dates do not match.
• 2- Breeding sites do not match.
• 3- Strict ritual of mating behavior, characteristic of a particular species.
• 4- Sperm from a foreign species cannot penetrate the egg.
• 5- If mating occurs, the hybrids have reduced viability.
• 6- Hybrids are sterile and cannot produce offspring.
• 7- Different sets of chromosomes

4) Give a definition of the concept “population”.

• Answer: A population is a collection of individuals of a given species, occupying a certain area of ​​territory within the species’ range, freely interbreeding with each other and partially or completely isolated from other populations.

5) Make the missing signatures on the presented diagram-model of the biological species. Use arrows to indicate possible migration of individuals.

§ 11- EVOLUTIONARY ROLE OF MUTATIONS

1) Complete the proposal.

• Answer: Priority in the study of genetic processes in the population belongs to the outstanding Russian scientist S. S. Chetvertikov.

2) Answer what is the evolutionary role of mutations.

• Answer: The mutation process is a source of reserve hereditary variability populations. By maintaining a high degree of genetic diversity in populations, it provides the basis for natural selection to operate.

3) Observations of natural populations show that most organisms are heterozygous for many genes. Give an explanation for this phenomenon.

• Answer: Most organisms are heterozygous for many genes, that is, their cells carry paired chromosomes different shapes the same gene. They are better adapted to the environment than homozygous ones.

4) Explain the reason(s) for differences in the genetic structure of populations of the same species.

• Answer: Genetic differences between populations exist because they often live in different environments. Directed changes in gene frequency are due to the action of natural selection.

5) Give a definition of the gene pool of a population (species).

• Answer: Gene pool of the population - is the totality of all genes in a population.

6) Write what the reserve of hereditary variability is and what is its biological significance.

• Answer:
• Reserve of hereditary variability - this is a mutation process.
• Its biological significance is mutations create the basis for genetic diversity of populations, which in the future can form new species. Mutations can lead to speciation.

7) Explain the meaning of the statement: “Some harmful mutations have positive evolutionary significance" Give an example.

• Answer: In some unusual conditions, mutations help to survive and give an advantage over other individuals. For example, some insects develop wings. Under normal conditions this is harmful, but when strong winds blow, it is to their benefit.

8) Choose the correct answer to the question from the options below and underline it.

Which (which) of the following factors is (are) the contributing factor(s) of the genetic heterogeneity of the population?

• Answer: insulation, mutation process, natural selection, population waves, migration.

9) Finish the sentence.

• Answer: An evolutionary factor that enhances and consolidates genetic differences between populations is insulation.

10) Give a definition of microevolution.

• Answer: Microevolution - These are changes in populations through natural selection that lead to speciation.