Lecture I. The problem of self-reproduction of biological systems.
The logical paradox of self-reproduction ("self-reversal"). Its reality: examples (lack of template reproduction of nucleotide sequences and/or reproduction of closed catalytic chains).
Conservative and non-conservative reproduction. Examples. Conservative reproduction is the only possible definition of self-reproduction of the “organism as a whole”. Non-conservative reproduction - reproduction of body parts (ontogenesis). Selection as the only logically possible combination of conservative self-reproduction with evolution.
Structure and information. Information and structural components of self-reproduction of phenotypes (example with the reproduction of phage Q?), difficulties with their differentiation. Similar difficulties with the differentiation of these components in higher organisms: the absence of fundamental differences between somatic cells and cells of the germ line, the syncretism of the genotype and phenotype. The impossibility of a correct definition of selection without distinguishing between the informational and structural components of self-reproduction.
The solution to the main paradox of self-reproduction is the von Neumann theorem. Genotype, phenotype and ontogeny as logically necessary elements of self-reproduction of living systems. The main consequences of the theorem are: the independence of the accuracy of reproduction of phenotypes from their structure and the possibility of introducing the concept of fitness, i.e., the fundamental possibility of selection evolution. Evolutionarily initial phenotype is a structure with the help of which information is reproduced.
Lecture II. Elementary life cycle.
The fundamental difference between the elementary life cycle and physical and biochemical cycles. Origin of biological information: separation of genotype and phenotype in connection with the emergence of the genetic code. The transition from the reproduction of the structure to the self-reproduction of its life cycle (when the structure that reproduces information does not change it). Reproduction accuracy as a single (and only) measure of phenotype fitness and the value of genetic information in the absence of environmental restrictions, when the competition of life cycles arises only due to self-reproduction errors (cycle reproduction errors give rise to its competitors). Cycles and hypercycles, the advantages of hypercycles: cooperation of polymerases and, most importantly, the emergence of its own variability in the hypercycle.
The emergence of competition in life cycles as the variability of self-reproduction systems decreases and the resource of the environment is exhausted. The difference between passive and active competition of elementary life cycles (hypercycles). Mathematical description of passive and active competition.
The main consequences of the emergence of a unified system of genetic self-reproduction of hypercycles is the possibility of self-reproduction at the intra-individual and supra-individual levels of organization. Accordingly, new directions of variability arise - the shuffling of genes within hypercycles and the union of hypercycles.
Finally, the emergence of competition leads to the structuring of fitness - the separation of the reproductive component and the survival component. Accordingly, alternative reproductive strategies appear - active (reproduction at the risk of life) and passive - experiencing adverse conditions.
Lecture IV. Generalized mathematical model of cooperative self-reproduction of two genes with bad promoters and overlapping regulatory regions. "Competitive exclusion" at the intra-individual level, the possibility of regular reproduction ("cloning") of alternative dynamic states of the hypercycle. The emergence of ontogenetic information, i.e. fixation of the path of development based on random selection. Emergence of competence to differentiate the ways of development and, as a result, the ontogenetic norm of reaction - the ability to form adaptive modifications. Adaptive modifications of prokaryotes: transition between lytic and lysogenic regimes in phages, SOS - system of bacteria, system of cell starvation, adaptive and constitutive syntheses, formation of operons. The general sequence of ontogeny formation: the emergence of a self-reproduction system? the formation of hypercycles? sweep formation? the emergence of competence to switch modes of self-reproduction? the emergence of adaptive modifications. Evolution of life cycles of prokaryotes based on the fixation of modifications.
Criticism of the von Neumann theorem. Coarse (physical) and non-coarse (information) systems. Von Neumann's theorem applies to non-rough systems without solving the question of their origin. Mixed nature of biological systems: coarse and non-rough ways of encoding genetic information (regulatory zones and reading frames). Form as information, non-rough systems can arise only on the basis of initial roughness.
The main difference between the structural and dynamic organization of prokaryotes and eukaryotes is the extension of the unfolding principle beyond the chromosome, while the chromosome itself ceases to be a unfolded. Spatial-temporal segregation of the nucleus and cytoplasm, translation and transcription, splicing.
Lecture V. Life cycles of Protozoa. The emergence of new ways of self-reproduction at the intra-individual and supra-individual levels of organization: the emergence of CMP, the center for the formation of microtubules, and the emergence of a single polar axis of cell movement and self-reproduction (an example is the asexual reproduction of ciliates). Self-reproduction as ontogeny. Examples of ontogenetic regulations (a part forms a whole). Amoeboid form and flagellar form as modulations (modifications) of the cell phenotype (prototypes of mesenchymal and epithelial cells of multicellular). Doublets of microtubules (MT) as analogues of cells of a multicellular organism. Playback of MT as a micro-scan. Examples of non-genetic inheritance of structures in ciliates.
Directions of evolution depending on the fate of CFM: single (nuclear) CFM (most of the lower Protozoa), doubling of CFM (higher flagellates), and MT polymerization with the disappearance of CFM (ciliates). In the first case, a unicellular organism is most vulnerable during reproduction (metazoic mitosis and the corresponding mitotic cycle), and is "saved" at the cost of complicating its life cycle.
Classification of life cycles according to the biological meaning of phase alternation: alternation of dividing and nomadic (or cyst-forming) cells, with the insertion of palintomic divisions and (or) growth. With the dominance of the haploid generation: n** (or *)? gametes* ? copulation? 2n (cyst) ?meiosis** ? n. With the dominance of the diploid generation: 2n* ? meiosis (cyst) gametes (settlement) ? copulation **? 2n. In general terms: trophozoid** ? zoospores *? trophozoid (* growth, ** palintomic divisions). This is nothing more than a prototype of the Metazoa life cycle.
Idealized Metazoa life cycle: syngamy, palintomic phase (flagellar cells), monotomic phase (amoeboid cells), gamete formation.
Lecture VI. Origin and evolution of Metazoa life cycles. Life cycles of intermediate forms (Volvox and social amoeba). A common feature is the refusal of some cells from self-reproduction in favor of other cells. For the formation of the life cycle, the differentiation of germ and somatic cells is not necessary. Metazoa ontogeny as the creation of a new form of supra-individual self-reproduction (a special case of the emergence of social behavior) based on cell differentiation. Selfish forms of cell reproduction in Volvox and social amoebae. Cellular differentiation as a spatial unfolding of the cell cycle (extension of the unfolding principle to the supracellular level of organization). Epithelium and mesenchyme as primary tissues.
Syngamy as cooperation of eggs (mitochondria, yolk) and sperm (CFM). Blastula as the primary form of a dispersing larva (“multicellular zoospore”), its evolutionary fate. Gastrulation as a metamorphosis of the primary larva, capturing all cells (many sponges), or part of the cells (sponges, coelenterates and higher Metazoa). The evolutionary fate of the gastrula (embryonic tissues). Separation of the germline as a secondary phenomenon. Difference between sex, stem, semi-stem and differentiated cells. Standard organ composition in adult Metazoa. The danger of selfish reproduction.
Metagenesis as an evolutionarily initial form of life cycle variability. Evolution of life cycles based on their own individual variability and intra-individual variability (neoteny and acceleration, paedomorphosis and hypermorphosis). Deployment and collapse of the life cycle (deembryonization and embryonization). Transition from phases of the life cycle to successive stages of ontogeny.
Compiled by prof. V.G. Cherdantsev
The fundamental differences between sexual and asexual reproduction is that sexual reproduction:
ensures the genetic constancy of the species
occurs only in higher organisms
provides combinative variability
The biological significance of meiosis (the sexual process) lies in the formation of cells involved in sexual reproduction, in maintaining the constancy of the species number of chromosomes; creating conditions for combinative variability and arbitrary divergence of parental chromosomes by gametes. Spores of mosses, ferns and some other groups of plants are formed by meiotic means. Violation of meiosis leads to pathological changes.
How many spermatozoa are formed as a result of spermatogenesis from two primary germ cells?
Spermatogenesis is the process of transformation of diploid spermatogonia (the precursors of germ cells) into spermatozoa. Spermatozoa after the second division proceed to the second meiotic division, as a result of which 4 haploid sex cells are formed. After differentiation, they become mature spermatozoa. Based on this, from the two primary germ cells, as a result of spermatogenesis, eight sperm.
The difference between oogenesis and spermatogenesis is that:
in oogenesis, four equivalent gametes are formed, and in spermatogenesis, one
in oogenesis, one complete gamete is formed, and in spermatogenesis, four
eggs contain more chromosomes than sperm
Features of spermatogenesis and oogenesis are that during the formation of spermatozoa, each of four daughter cells is complete and capable of fertilizing the egg. But during the maturation of eggs, meiotic division occurs differently: the cytoplasm is distributed unevenly between daughter cells. However, only one of the four cells formed, it becomes a viable egg.
How many divisions of the original cell occur in gametogenesis?
In gametogenesis, the parent cell share once.
The number of germ cells formed in the body, most likely, may depend on:
storage of nutrients in the cell
individual age
probabilities of meeting gametes with each other
Asexual reproduction dominates the life cycle:
hydra
sharks
Maybug
In the life of a hydra asexual reproduction is dominant over the floor. Asexual reproduction occurs by budding. A protrusion occurs on the body of the hydra, which captures the ecto- and endoderm. The resulting kidney increases in size, a constriction forms at its base, and a mouth opening appears, surrounded by tentacles. The formed young hydra buds off the parent.
Gametes in ferns are formed:
on the leaves
in disputes
on sprouts
The gametophyte in a fern begins with the development of a tiny, pale green chain of algae-like cells. Then a flat heart-shaped membranous structure is formed from it - sprout with numerous rhizoids in the center of the lower surface. In the same place, on the lower surface, antheridia and archegonia are formed. Antheridia usually appear earlier and archegonia later. Numerous spirally twisted many flagellated spermatozoa are formed in the antheridia.
Endosperm in flowering plants is formed by fusion.
sperm and eggs
polar nucleus and sperm
two polar nuclei and sperm
After one of the sperm fertilizes the egg, a diploid zygote is formed (the embryo of a new plant organism develops from it). Second sperm fuses with two polar nuclei(or with a central diploid nucleus), forming a triploid cell, from which the nutritive tissue, the endosperm, subsequently arises. Its cells contain a supply of nutrients necessary for the development of the plant embryo.
Double fertilization occurs in
cuckoo flax moss
Scotch pine
chamomile officinalis
Chamomile belongs to the Angiosperms, or Flowering Plants, while pine and moss belong to different groups. Flowering plants are characterized double fertilization.
A form of reproduction in which the hereditary information of the offspring is identical to that of the mother.
sexual
asexual
budding
A form of reproduction in which a new organism develops from a zygote.
sexual
asexual
both answers are correct
At sexual reproduction, an individual of each next generation arises as a result of the fusion of two specialized haploid cells - gametes. Most often, gametes are formed in special organs of male and female individuals. As a result of fertilization, the chromosomes of the egg and sperm are in the same nucleus, a zygote is formed - the first cell of a new organism.
The value of crossing over in meiosis.
increases sperm count
reduces the number of eggs
Crossing over involves the exchange of identical regions of homologous chromosomes. This is increases the genetic diversity of germ cells, since as a result of this process, chromosomes are formed that carry the genes of both the father and the mother. Thus, meiosis underlies combinative variability.
What is the advantage of double fertilization in angiosperms.
in the formation of mechanical tissue
in the formation of nutritional tissue
in the formation of the embryo
Comparing two methods of reproduction - asexual and sexual, we can conclude that asexual reproduction leads to the appearance of individuals that are genetic copies of the parent. This method is ideal for breeding in stable, unchanging environmental conditions. On the contrary, sexual reproduction promotes the recombination of parental genes and, therefore, the diversity of offspring. This method of reproduction is very important for the evolutionary progress of the species ( prosperity of the species) in constantly changing conditions of existence.
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