home Auditorium 8 What is the advantage of sexual reproduction in comparison. How does sexual reproduction differ from asexual reproduction? Features of reproduction. Advantages of sexual and asexual reproduction

What is the advantage of sexual reproduction in comparison. How does sexual reproduction differ from asexual reproduction? Features of reproduction. Advantages of sexual and asexual reproduction

1. What is the advantage of sexual reproduction over asexual reproduction?

Answer. During sexual reproduction, which is carried out by the fusion of two sex cells of gametes, genetic information of the parents is exchanged. As a result, offspring appear diverse in their characteristics, which can surpass their parents in viability, including when environmental conditions change.

2. Give examples of organisms that reproduce primarily asexually.

Answer. In asexual reproduction, a new organism can arise from one or more asexual (somatic) cells of the mother.

Prokaryotic cells reproduce by dividing in two. Many protozoa (amoeba, green euglena, etc.), unicellular algae (Chlamydomonas) reproduce by normal mitotic cell division. Other unicellular and some lower fungi, algae (chlorella), animals (malarial plasmodium) are characterized by sporulation. It lies in the fact that the cell breaks up into a large number of individuals equal to the number of nuclei previously formed in the parent cell as a result of repeated division of its nucleus.

Questions after § 32

1. What is the difference between conjugation and copulation?

Answer. If we are talking about methods of sexual reproduction, then:

during copulation, two single-celled individuals merge (the genetic information of both parents is combined, and then divide by meiosis (the number of individuals that have received genetic information from both parents increases).

during conjugation, genetic information is exchanged without increasing the number of individuals. The following main forms of conjugation are distinguished: isogamy, anisogamy and oogamy.

With isogamy, mobile, morphologically identical gametes are formed. Isogamy occurs in many algae.

With heterogamy, mobile gametes differing morphologically and physiologically are formed. This type of sexual process is characteristic of many algae.

In the case of oogamy, the gametes are very different from each other. The female gamete is a large, immobile egg containing a large supply of nutrients. Male gametes - sperm - are small, most often motile cells that move with the help of one or more flagella. Oogamy is characteristic of animals, higher plants and many fungi.

2. Where are eggs formed?

Answer. The egg is the female gamete of animals, higher plants, as well as many algae and unicellular organisms, which are characterized by oogamy. In animals, eggs are formed in the female sex glands - the ovaries, in gymnosperms and angiosperms in the ovules, in mosses and ferns in archegonia

3. What is the sperm acrosome needed for?

Answer. During fertilization, at the moment of contact of the sperm with the egg, the enzymes contained in the acrosome are released and dissolve the egg membranes, ensuring the penetration of the sperm into the egg.

The main process is natural selection. It decides which adaptations for a given habitat are favorable and which are not so desirable. If the adaptation is favorable, then organisms that have , encoding that trait, will live long enough to reproduce and pass on their genes to the next generation.

In order for natural selection to work on a population, there must be diversity. To obtain diversity in individuals, different genetics and expressions are required. All this depends on the method of reproduction of a particular species.

Asexual reproduction

Asexual reproduction is the production of offspring from one parent, which is not accompanied by mating or mixing of genes. Asexual reproduction results in cloning of the parent, meaning the offspring has identical DNA to its ancestor. As a rule, there is a lack of species diversity from generation to generation.

One way to gain some species diversity is through mutations at the DNA level. If an error occurs in the process or copying of DNA, then this error will be passed on to the offspring, possibly changing their traits. However, some mutations do not change the phenotype, so not all changes in asexual reproduction result in variation in the offspring.

Sexual reproduction

Sexual reproduction occurs when a female reproductive cell (egg) combines with a male cell (sperm). An offspring is a genetic combination of mother and father, with half of its chromosomes coming from one parent and the other half from the other. This ensures that the offspring are genetically different from their parents and even siblings.

Mutations can also occur in sexually reproducing species to further increase the diversity of the offspring. The process that creates the (sex cells) used for reproduction also helps increase diversity. It ensures that the resulting gametes are genetically different. Independent recruitment during meiosis and random fertilization also influences gene mixing and allows offspring to better adapt to their environment.

Reproduction and evolution

As a rule, it is believed that sexual reproduction contributes more to evolution than asexual reproduction, since it has a much greater

The essence of sexual reproduction is the creation of new genetic combinations. In the most typical cases, a male and a female mate and produce individuals whose genotypes are not identical to either the genotype of the father or the genotype of the mother. In some animals, new genotypes can be created as a result of processes of a different kind. In protozoa such as paramecia, autogamy occurs, in which one individual creates new homozygous genotype. Other forms, including some flatworms and molluscs, are hermaphroditic, i.e. have both male (sperm-producing) and female (egg-producing) gonads. There are hermaphroditic forms that are capable of self-fertilization.

Not all reproduction is sexual (that is, it creates new genotypes). For example, paramecia are capable of dividing in two to form two new daughter organisms, genetically identical to the original individual. Hydroid polyps (one of the groups of coelenterates) can produce new individuals identical to themselves as a result of the budding process. In this case, several new organisms can form in one budding zone. Other animals, including many insects and some fish, are capable of parthenogenetic reproduction, in which offspring develop from unfertilized eggs

The vast majority of animals, especially forms that have arisen relatively recently, reproduce sexually, that is, by the fusion of male and female gametes. Theorists disagree about the reasons for this predominance of the sexual process. Since sexual reproduction requires certain costs, it obviously must provide some significant advantages. The following main reasons have been put forward for explanation:

1) an evolutionary advantage for populations that can change faster than others through sexual reproduction;

2) evolutionary advantage due to the fact that this method of reproduction facilitates speciation (the emergence of new species);

3) that individual parents can create diversity in their immediate offspring, making it easier for them to adapt to unpredictable changes in the environment.

During sexual reproduction, as a result of the fusion of gametes, a fertilized egg is formed - a zygote, which carries the hereditary inclinations of both parents, due to which the hereditary variability of the descendants sharply increases. This is the advantage of sexual reproduction over asexual reproduction. Those. in the presence of genetic recombination, parental individuals produce offspring that will differ from them in the most unpredictable way, and among new random combinations of genes, at least half may turn out to be worse than the parent genotype, however, the shuffling of genes during sexual reproduction contributes to the survival of the species when environmental conditions change. If a parent produces many offspring with a wide variety of gene combinations, there is a greater chance that at least one offspring will be well suited for future life circumstances, whatever they may be.

In the presence of genetic recombination, parental individuals produce offspring that will differ from them in the most unpredictable ways, and among the new random combinations of genes, at least half may turn out to be worse than the parent genotype, but the shuffling of genes during sexual reproduction contributes to the survival of the species when environmental conditions change. If a parent produces many offspring with a wide variety of gene combinations, there is a greater chance that at least one offspring will be well suited for future life circumstances, whatever they may be.

Many hypotheses have been proposed to explain the advantages of sexual reproduction in the struggle for existence. One of them gives an idea of what the first stages of the evolution of sexual reproduction might have been. The course of evolution depends largely on mutations, which change existing genes, forming instead new alleles (variants) of these genes. Suppose that two individuals in a certain population have favorable mutations that affect certain genetic loci, and therefore different functions. In an asexual species, each of these individuals will give rise to a clone of mutant offspring, and the two new clones will compete until one of them wins. One of the favorable alleles produced by mutation will thus spread, while the other will eventually disappear. Now imagine that one of the original mutants has a genetically determined feature that allows it from time to time to include genes from other clones into its genome. In conditions of the struggle for existence, the acquisition of genes from cells of a competing clone is equivalent to the creation of a cell that carries all the favorable mutations. Such a cell will have the greatest fitness, and the advantages it receives will ensure the spread in the population of a feature that allows it to include genes from other cells in its genome. Natural selection will favor such primitive sexual reproduction.

Spermatozoa are one of the main characters in sexual reproduction.

Yeast has helped scientists show that interbreeding leads to greater ecological adaptability of a species.
The survival of a species is associated with the accumulation of genetic changes that help the organism survive in a particular habitat. It is believed that sexual reproduction, which increases genetic variability, contributes to the rapid evolution of the species. But in the case of sexual reproduction, the offspring takes on the genes of two different individuals. Let's imagine that the mother and father came from different populations; The mother’s genes allow her to survive under certain conditions, while the father’s genes are “tailored” for others. The offspring in this case will not be adapted to either one or the other: the genes will weaken each other and will not be able to work adequately under any conditions at all. It turns out that sexual reproduction does not contribute to the survival of the species?

Researchers from the University of Auckland (New Zealand) set up an experiment that was supposed to directly answer the question of whether interbreeding between populations helps or hinders evolution. Scientists used yeast, which can reproduce both asexually and sexually. The first crop was grown under one conditions, the second - under different ones. At some point, the yeast switched on the mechanism of sexual reproduction and made it possible for fungi from different populations to find each other.

In a paper published in the journal Ecology Letters, the authors write that offspring produced through sexual reproduction adapted more quickly to their environment. If the parents were from different populations, then their children felt equally well in both “maternal” and “paternal” environmental conditions. That is, sexual reproduction not only does not interfere, but also stimulates the evolution of the species, especially when individuals from different populations meet.

In fact, the results of the experiment confirm one alternative, but relatively little-known hypothesis, according to which genes “tailored” to one condition do not necessarily interfere with life in another. Genes for different environments do not come into confrontation, but coexist peacefully in one genome, turning on and off as needed.

Previously, evolutionary biologists had to come up with clever tricks that were supposed to prevent individuals from different populations from interbreeding with each other and thereby weaken the evolutionary position of the species. And although, as already mentioned, there was an alternative hypothesis, experimental confirmation was necessary to raise it above all others. When preparing this article, compulsory information was used.

Topic: "REPRODUCTION AND DEVELOPMENT OF ORGANISMS
Methods of reproduction of organisms"

Seminar 2 hours

Municipal educational institution gymnasium No. 10 of Murmansk
Teacher: Podmyatnikova L.S. , biology teacher, winner of the competition for the best teachers of the Russian Federation (NPPO)

11th grade

Goals:

Students must learn the concepts of “asexual reproduction, sexual reproduction, vegetative reproduction, sporulation, fragmentation, budding, gametes, hermaphrodism, conjugation, parthenogenesis, ovaries, testes, egg, sperm, gametogenesis, oogenesis, spermatogenesis, guide bodies, reproduction zone, growth zone , maturation zone, fertilization, zygote, double fertilization, microspores, megaspores, pollen grain, embryo sac”, know the essence of the processes of gametogenesis, fertilization, advantages and disadvantages of asexual and sexual methods of reproduction.

Students should be able to independently work through educational material, compare biological processes, give a reasoned answer, draw conclusions, and apply knowledge in a non-standard situation.

Contribute to the formation of a scientific worldview and communication skills in students.
Reproduction is reproduction
their own kind through their own dissimilar ones.

Progress of the lesson.

I. ACTUALIZATION OF KNOWLEDGE, INTRODUCTION TO THE TOPIC.
In the last lesson, we studied in detail the different methods of cell division, which underlie the reproduction and development of not only unicellular, but also multicellular organisms.
-What is the main difference between mitosis and meiosis?
- What is the biological significance of mitosis? meiosis?
The ability to reproduce is one of the most important features of living things. During the process of reproduction, genetic material is transferred from parents to offspring. The importance of reproduction for the species as a whole consists in the continuous replenishment of the number of individuals of a given species dying for various reasons. In addition, reproduction allows, under favorable conditions, to increase the number of individuals.
The process of reproduction is one of the most diverse in nature. In some cases, reproduction occurs continuously throughout the life of the organism, in others - only once. Sometimes reproduction begins after the individual stops growing, and sometimes it is possible during the growth process. Reproduction methods can be divided into two groups: asexual and sexual (slide 3). . Although sexual reproduction is rightfully considered a more progressive method, many organisms in their life cycle have retained the ability to reproduce asexually (slide 4).
- Why hasn't sexual reproduction completely replaced asexual reproduction?

II. LEARNING NEW MATERIAL
Let's get acquainted with the features and forms of asexual reproduction
1. Asexual reproduction of organisms - oral answer, discussion
So, asexual reproduction is widespread in nature. The following features are characteristic (slide 5). :

only one individual takes part in reproduction;
carried out without the participation of germ cells;
Reproduction is based on mitosis and meiosis (formation of spores in plants);
the offspring are identical and are exact genetic copies of the mother.

Forms of asexual reproduction are varied (slide 6).

A). Binary fission is a division in which two equal daughter cells (amoeba) are formed - (slide 7).

B) Multiple fission, or schizogony. The mother cell breaks up into a large number of more or less identical daughter cells (malarial plasmodium).

B) Sporulation. Reproduction through spores - specialized cells of fungi and plants. If the spores have a flagellum and are motile, then they are called zoospores (Chlamydomonas) (slide 8).

D) Budding. On the mother individual, an outgrowth is formed - a bud, from which a new individual (yeast, hydra) develops (slide 9).

D) Fragmentation is the division of an individual into two or more parts, each of which develops into a new individual. In plants (spirogyra) and animals (anneli). Fragmentation is based on the property of regeneration.

E) Reproduction by parts of vegetative organs. Characteristic of many groups of plants. During vegetative propagation, a new individual develops either from a part of the mother or from special structures (bulb, tuber, etc.) specifically designed for vegetative propagation.

G) Polyembryony. Reproduction during embryonic development, in which several embryos develop from one zygote - twins (identical twins in humans). Offspring are always the same sex (slide 10).

H) Cloning. An artificial method of asexual reproduction. Not found in natural conditions. A clone is a genetically identical offspring obtained from one individual as a result of one or another method of asexual reproduction (slide 11)..
Exercise 1. Can offspring produced by asexual reproduction have characteristics that distinguish them from those of the maternal organism?
Checking progress.
Let's identify the advantages and disadvantages of asexual reproduction (slide 12)

1. Sexual reproduction. Methods of sexual reproduction - oral answer, discussion
Features of sexual reproduction (slide 13):
2 parents involved
Gametes are formed - sex cells
Fertilization occurs
The process of meiosis is based on
Descendants are genetically heterogeneous.

2. The structure of gametes. Gametogenesis – oral response, discussion(slide 14)
Task 2. Consider Fig. 1. and fill out the table “Formation of germ cells”

Fig 1. Scheme of formation of germ cells

Formation of germ cells

What are the main similarities and main differences in these processes?
Checking progress (slide 15).

Additions.

The size of eggs varies widely - from several tens of micrometers to several centimeters (a human egg is about 100 microns, an ostrich egg, which has a length with a shell of about 155 mm, is also an egg).
During oogenesis, the egg accumulates all the necessary substances for the initial stages of embryonic development. The methods for obtaining these substances are different: in lower animals - by phagocytosis of neighboring cells by the egg, in higher animals - from follicular cells through cytoplasmic bridges (insects) or gap junctions (vertebrates). In this case, the yolk is often synthesized in organs far from the egg, for example, in liver cells. The yolk is usually concentrated at the vegetative pole, and the nucleus at the animal pole. In addition to the yolk, the egg accumulates some organelles - ribosomes (up to 10 13). Amplification of r-RNA genes occurs (millions of copies). The egg cell forms another shell on top of the membrane - the primary one. It consists of glycoproteins and is involved in species-specific recognition of sperm. In many animals, secondary (secreted by follicular cells) and tertiary (secreted by the walls of the oviducts) egg shells are also formed. They are formed after fertilization. Example - protein, parchment shell, bird egg shell. Cortical granules accumulate under the egg shell - membrane vesicles involved in fertilization. In mammals, eggs have a zona pellucida, on top of which is the corona radiata, a layer of follicular cells.
Cells that have completed mitotic division are 1st order oocytes. In humans, even during the embryonic development of the female body, oocytes enter prophase of the 1st division of meiosis and remain at this stage for 12–13 years – until puberty. Only after this, under the influence of sex hormones, periodically some oocytes complete the 1st division of meiosis and become haploid - oocytes of the 2nd order. Fertilization occurs at the metaphase II stage. After fertilization, the process of meiosis is completed and the oocytes become mature eggs. If fertilization does not occur, the oocyte is destroyed.

3. Fertilization - oral response, discussion(slide 16, 17)
Addition.
The eggs of many animals secrete two types of non-protein substances: the first activate the movement of sperm, the second cause their gluing. Sperm also secrete substances that slow down the movement of other sperm. The sperm binds using the bindin protein to the glycoprotein receptors of the primary shell of the egg. bindins vary even among closely related species.
After attachment of the sperm, the area of the primary membrane dissolves and the outer membranes of the sperm and egg merge. Most often, the sperm is completely retracted into the egg; sometimes the flagellum remains outside and is discarded. From the moment the sperm penetrates the egg, the gametes cease to exist, as they form a single cell - the zygote. Depending on the number of sperm that penetrate the egg during fertilization, they are distinguished: monospermy - fertilization in which only one sperm penetrates the egg (the most common fertilization), and polyspermy - fertilization in which several sperm penetrate the egg. But even in this case, the nucleus of only one of the sperm merges with the nucleus of the egg, and the remaining nuclei are destroyed.
Cortical granules fuse with the outer membrane, and their contents are poured under the primary membrane. As a result, the primary shell separates from the outer membrane and becomes harder. It is called the fertilization membrane. These processes prevent polyspermy.

Task 3*.

In general, the process of fertilization is similar for most animals, but in particular it has quite significant differences, ranging from mating behavior, methods of fertilization to differences in the mechanisms of penetration of sperm into the egg. What do you think is the biological meaning of such diversity?
Task 4*. Experimentally, you can destroy the nucleus of an egg with X-rays or ultraviolet radiation, and then fertilize it with two sperm. After the fusion of their nuclei, full-fledged offspring can develop. How will the results of such experiments differ between birds and mammals?
Checking progress.

4. Double fertilization in flowering plants - oral answer, discussion