Genetics- a science that studies genes, mechanisms of inheritance of traits and variability of organisms. During the process of reproduction, a number of traits are passed on to the offspring. It was observed back in the nineteenth century that living organisms inherit the characteristics of their parents. The first to describe these patterns was G. Mendel.
Heredity– the property of individual individuals to transmit their characteristics to their offspring through reproduction (through reproductive and somatic cells). This is how the characteristics of organisms are preserved over a number of generations. When transmitting hereditary information, its exact copying does not occur, but variability is always present.
Variability– the acquisition by individuals of new properties or the loss of old ones. This is an important link in the process of evolution and adaptation of living beings. The fact that there are no identical individuals in the world is due to variability.
Inheritance of characteristics is carried out using elementary units of inheritance - genes. The set of genes determines the genotype of an organism. Each gene carries encoded information and is located in a specific place in the DNA.
Genes have a number of specific properties:
- Different traits are encoded by different genes;
- Constancy - in the absence of a mutating effect, the hereditary material is transmitted unchanged;
- Lability – the ability to succumb to mutations;
- Specificity - a gene carries special information;
- Pleiotropy – one gene encodes several traits;
Under the influence of environmental conditions, the genotype gives different phenotypes. The phenotype determines the degree to which the organism is influenced by environmental conditions.
Allelic genes
The cells of our body have a diploid set of chromosomes; they, in turn, consist of a pair of chromatids, divided into sections (genes). Different forms of the same genes (for example, brown/blue eyes), located in the same loci of homologous chromosomes, are called allelic genes. In diploid cells, genes are represented by two alleles, one from the father and one from the mother.
Alleles are divided into dominant and recessive. The dominant allele determines which trait will be expressed in the phenotype, and the recessive allele is inherited, but does not manifest itself in a heterozygous organism.
There are alleles with partial dominance, such a condition is called codominance, in which case both traits will appear in the phenotype. For example, flowers with red and white inflorescences were crossed, resulting in red, pink and white flowers in the next generation (pink inflorescences are a manifestation of codominance). All alleles are designated by letters of the Latin alphabet: large - dominant (AA, BB), small - recessive (aa, bb).
Homozygotes and heterozygotes
Homozygote is an organism in which alleles are represented only by dominant or recessive genes.
Homozygosity means having the same alleles on both chromosomes (AA, bb). In homozygous organisms, they code for the same traits (for example, the white color of rose petals), in which case all offspring will receive the same genotype and phenotypic manifestations.
Heterozygote is an organism in which alleles have both dominant and recessive genes.
Heterozygosity is the presence of different allelic genes in homologous regions of chromosomes (Aa, Bb). The phenotype of heterozygous organisms will always be the same and is determined by the dominant gene.
For example, A – brown eyes, and – blue eyes, an individual with genotype Aa will have brown eyes.
Heterozygous forms are characterized by splitting, when when crossing two heterozygous organisms in the first generation we get the following result: by phenotype 3:1, by genotype 1:2:1.
An example would be the inheritance of dark and light hair if both parents have dark hair. A is a dominant allele for dark hair, and is recessive (blond hair).
R: Aa x Aa
G: A, a, a, a
F: AA:2Aa:aa
*Where P – parents, G – gametes, F – offspring.
According to this diagram, you can see that the probability of inheriting a dominant trait (dark hair) from parents is three times higher than a recessive one.
Diheterozygote- a heterozygous individual that carries two pairs of alternative characteristics. For example, Mendel's study of the inheritance of traits using pea seeds. The dominant characteristics were yellow color and smooth seed surface, while the recessive characteristics were green color and rough surface. As a result of the crossing, nine different genotypes and four phenotypes were obtained.
Hemizygote- this is an organism with one allelic gene, even if it is recessive, it will always manifest itself phenotypically. Normally they are present on sex chromosomes.
Difference between homozygote and heterozygote (table)
| Differences between homozygous and heterozygous organisms | ||
|---|---|---|
| Characteristic | Homozygote | Heterozygote |
| Alleles of homologous chromosomes | Identical | Different |
| Genotype | AA, aa | Aa |
| The phenotype is determined by the trait | By recessive or dominant | By dominant |
| First generation monotony | + | + |
| Split | Doesn't happen | From the second generation |
| Manifestation of a recessive gene | Characteristic | Suppressed |
Reproduction and crossing of homozygotes and heterozygotes leads to the formation of new characteristics that are necessary for living organisms to adapt to changing environmental conditions. Their properties are necessary when breeding crops and breeds with high quality indicators.
One of the levels of organization of living matter is gene- a fragment of a nucleic acid molecule in which a certain sequence of nucleotides contains the qualitative and quantitative characteristics of one characteristic. An elementary phenomenon that ensures the contribution of a gene to maintaining the normal level of vital activity of the organism is the self-reproduction of DNA and the transfer of the information contained in it into a strictly defined nucleotide sequence of transfer RNA.
Allelic genes- genes that determine the alternative development of the same trait and are located in identical regions of homologous chromosomes. So, heterozygous individuals have two genes in each cell - A and a, which are responsible for the development of the same trait. Such paired genes are called allelic genes or alleles. Any diploid organism, be it a plant, animal or human, contains two alleles of any gene in each cell. The exception is sex cells - gametes. As a result of meiosis, one set of homologous chromosomes remains in each gamete, so each gamete has only one allelic gene. Alleles of the same gene are located in the same place on homologous chromosomes. Schematically, a heterozygous individual is designated as follows: A/a. Homozygous individuals with this designation look like this: A/A or a/a, but they can also be written as AA and aa.
Homozygote- a diploid organism or cell that carries identical alleles on homologous chromosomes.
Gregor Mendel was the first to establish a fact indicating that plants that are similar in appearance can differ sharply in hereditary properties. Individuals that do not split in the next generation are called homozygous.
Heterozygous are called diploid or polyploid nuclei, cells or multicellular organisms, copies of genes of which are represented by different alleles on homologous chromosomes. When a given organism is said to be heterozygous (or heterozygous for gene X), this means that the copies of the genes (or of a given gene) on each of the homologous chromosomes are slightly different from each other.
20. The concept of a gene. Gene properties. Gene functions. Types of genes
Gene- a structural and functional unit of heredity that controls the development of a certain trait or property. Parents pass on a set of genes to their offspring during reproduction.
Gene properties
Allelic existence – genes can exist in at least two different forms; Accordingly, paired genes are called allelic.
Allelic genes occupy identical places on homologous chromosomes. The location of a gene on a chromosome is called a locus. Allelic genes are designated by the same letter of the Latin alphabet.
Specificity of action - a certain gene ensures the development of not just any trait, but a strictly defined one.
Dosage of action - the gene ensures the development of the trait not indefinitely, but within certain limits.
Discreteness - since the genes on a chromosome do not overlap, in principle a gene develops a trait independently of other genes.
Stability - genes can be passed on without any changes over a number of generations, i.e. the gene does not change its structure when transmitted to subsequent generations.
Mobility - with mutations, a gene can change its structure.
Gene function, its manifestation lies in the formation of a specific characteristic of the organism. Removal of a gene or its qualitative change leads, respectively, to the loss or change of the trait controlled by this gene. At the same time, any sign of an organism is the result of the interaction of a gene with the surrounding and internal, genotypic environment. The same gene can take part in the formation of several characteristics of an organism (the phenomenon of so-called pleiotropy). The bulk of traits are formed as a result of the interaction of many genes (the phenomenon of polygeny). At the same time, even within a related group of individuals in similar living conditions, the manifestation of the same gene can vary in degree of expression (expressiveness, or expression). This indicates that in the formation of traits, genes act as an integral system that strictly functions in a certain genotypic and environmental environment.
Types of genes.
Structural genes - carry information about the first protein structure
Regulatory genes - do not carry information about the first structure of the protein, but regulate the process of protein biosynthesis
Modifiers – capable of changing the direction of protein synthesis
See also:
- HOMIOTHERMAL ANIMALS(from the Greek homoios - equal, identical and therme - warmth), or warm-blooded (syn. homeothermic and homothermic animals), those animals that have a regulatory apparatus that allows them to maintain body temperature approximately constant and almost independent ...
- HOMOLOGICAL SERIES, groups of organic compounds with the same chemical. function, but differing from each other in one or more methylene (CH2) groups. If in the simplest compound of a number of saturated hydrocarbons - methane, CH4, one of...
- HOMOLOGY ORGANS(from the Greek ho-mologos - consonant, corresponding), the name of morphologically similar organs, i.e. organs of the same origin, developing from the same rudiments and revealing similar morphol. ratio. The term “homology” was introduced by the English anatomist R. Owen for...
- HOMOPLASTY, or homoyoplasty (from the Greek homoios-like), isoplasty, free transplantation of tissues or organs from one individual to another of the same species, including from one person to another. Start...
- HOMOSEXUALITY, unnatural sexual attraction to persons of the same sex. G. was previously considered a purely psychopathological phenomenon (Krafft-Ebing), and G.’s issues were dealt with primarily by psychiatrists and forensic doctors. Only recently, thanks to the work...
HETEROSYGOTE - (from hetero... HETEROSYGOTE - HETEROSYGOTE, an organism that has two contrasting forms (ALLELES) of a GENE in a pair of CHROMOSOMES. Heterozygote is an organism that has allelic genes of different molecular forms; in this case, one of the genes is dominant, the other is recessive. Recessive gene - an allele that determines the development of a trait only in a homozygous state; such a trait will be called recessive.
Heterozygosity, as a rule, determines the high viability of organisms and their good adaptability to changing environmental conditions and is therefore widespread in natural populations.
The average person has approx. 20% of genes are in a heterozygous state. That is, the allelic genes (alleles) - paternal and maternal - are not the same. If we designate this gene with the letter A, then the body’s formula will be AA. If the gene is received from only one parent, then the individual is heterozygous. The development of a trait depends both on the presence of other genes and on environmental conditions; the formation of traits occurs during the individual development of individuals.
Mendel called the trait manifested in first-generation hybrids dominant, and the suppressed trait recessive. Based on this, Mendel made another conclusion: when crossing hybrids of the first generation, the characteristics in the offspring are split in a certain numerical ratio. In 1909, V. Johansen called these hereditary factors genes, and in 1912, T. Morgan showed that they are located in chromosomes.
HETEROSYGOTE is:
During fertilization, the male and female gametes fuse and their chromosomes combine to form a single zygote. From self-pollination of 15 first-generation hybrids, 556 seeds were obtained, of which 315 were yellow smooth, 101 yellow wrinkled, 108 green smooth and 32 green wrinkled (splitting 9:3:3:1). Mendel's third law is valid only for those cases when the genes for the analyzed traits are located in different pairs of homologous chromosomes.
As a rule, it is a consequence of the sexual process (one of the alleles is introduced by the egg, and the other by the sperm). Heterozygosity maintains a certain level of genotypic variability in a population. Wed. Homozygote. In experiments, G. is obtained by crossing homozygotes for various types with each other. alleles.
Source: “Biological Encyclopedic Dictionary.” Ch. ed. M. S. Gilyarov; Editorial team: A. A. Babaev, G. G. Vinberg, G. A. Zavarzin and others - 2nd ed., corrected. Eg. Both parents may have blue eyes, but one of them has curly hair and the other has smooth hair. Lit.: Bateson W., Mendel’s principles of heredity, Cambridge, 1913; see also literature to Art. Genetics.A.
Genetics is the science of the laws of heredity and variability. Heredity is the property of organisms to transmit their characteristics from one generation to another. Variability is the property of organisms to acquire new characteristics compared to their parents.
The main one is the hybridological method - a system of crossings that allows us to trace the patterns of inheritance of traits in a number of generations. First developed and used by G. Mendel. Crossing, in which the inheritance of one pair of alternative characters is analyzed, is called monohybrid, two pairs - dihybrid, several pairs - polyhybrid. Mendel came to the conclusion that in first-generation hybrids, of each pair of alternative characters, only one appears, and the second seems to disappear.
When monohybrid crossing of homozygous individuals having different values of alternative characteristics, the hybrids are uniform in genotype and phenotype. The experimental results are shown in the table. The phenomenon in which part of the second generation hybrids carries a dominant trait, and part - a recessive one, is called segregation.
From 1854, for eight years, Mendel conducted experiments on crossing pea plants. To explain this phenomenon, Mendel made a number of assumptions, which were called the “gamete purity hypothesis”, or the “gamete purity law”. At the time of Mendel, the structure and development of germ cells had not been studied, so his hypothesis of the purity of gametes is an example of brilliant foresight, which later found scientific confirmation.
Organisms differ from each other in many ways. Therefore, having established the patterns of inheritance of one pair of traits, G. Mendel moved on to studying the inheritance of two (or more) pairs of alternative traits. As a result of fertilization, nine genotypic classes may appear, which will give rise to four phenotypic classes.
Certain alleles are defined. Determining heterozygosity for recessive alleles that cause hereditary diseases (i.e., identifying carriers of this disease) is an important medical problem. genetics.
HOMOLOGICAL SERIES, groups of organic compounds with the same chemical. function, but differing from each other in one or more methylene (CH2) groups. HOMOLOGICAL ORGANS (from the Greek ho-mologos - consonant, corresponding), the name of morphologically similar organs, i.e. Alternative features are understood as different meanings of a feature, for example, the feature is the color of peas, alternative features are the yellow color, the green color of peas.
For example, in the presence of a “normal” allele A and mutant a1 and a2, the a1/a2 heterozygote is called. compound, unlike heterozygotes A/a1 or A/a2. (see HOMOZYGOTE). However, when breeding heterozygotes in the offspring, the valuable properties of varieties and breeds are lost precisely because their germ cells are heterogeneous. The yellow color (A) and smooth shape (B) of the seeds are dominant traits, the green color (a) and wrinkled shape (b) are recessive traits.
- Homozygous organism is an organism (animal or plant) that has two absolutely identical genes, for example, two dominant black genes (BB) or two recessive brown genes (bb). Based on this characteristic, this organism is called pure.
- Heterozygous organism is an organism containing one dominant and one recessive gene (for example, Bb). Such an organism is called a hybrid.
Homo is translated from Latin as the same; a homozygous trait is a trait that is inherited in the body by the same gene, which is in a paired state (AA). Therefore, a homozygous organism is an organism in which a trait is inherited by the same gene.
A dominant trait is denoted by the letter A, a recessive trait is denoted by the letter a.
Hetero is translated from Latin as different, this is when in an organism a trait can be inherited both by a dominant and a recessive, i.e. there may be inheritance of traits like AA, Aa and aa. In the first two cases, the trait is inherited as a dominant, and in the second case as a recessive. Therefore, a heterozygous organism is an organism in which a trait is inherited by different genes.
In order to understand what we are talking about in general, it is necessary to understand genes, or rather, their division into dominant and recessive...
Dominant genes are those genes that dominate others, fight for their victory...
Recessive genes are those genes that are suppressed and cannot fight dominant ones...
So homozygous organisms contain two dominant genes (from the word homo - identical)...
Heterozygous organisms contain different genes, one dominant, the other recessive (from the word hetero - different)...
So the fundamental difference is that genes can be either identical in power or different...
The medical encyclopedia has a definition
Homozygous sex is a sex that has 2 identical sex chromosomes. In a homozygous (from the Greek homos means same and zygote means paired) organism, there are 2 identical copies of a particular gene on homologous chromosomes.
A heterozygous sex is a sex that has different sex chromosomes or just one chromosome. In a heterozygous organism, also called a hybrid organism, by definition there are two different forms of a particular gene (different forms of a gene) on homologous chromosomes.
These are very complex definitions for those who have not encountered such concepts, but a very clear explanation is given by the biological encyclopedia, see the link here.
homo - homogeneous.
hetero - heterogeneous.
For organisms, this means that if the allelic genes are the same, then the organism is homozygous, and if they are different, then it is heterozygous, which can be used when crossing two organisms.
Homozygous and heterozygous organisms differ from each other by the presence or absence of two identical genes. U homozygous organisms, or whether both traits are dominant or recessive (for example, dark hair and brown eyes). U heterozygous one of the traits is dominant and the other is recessive (for example, blond hair and brown eyes).
Homozygous (homo - identical) are those organisms in which two genes are equally dominant in the entire organism.
Hererozygous (hetero - different) - those organisms in which two genes are different, i.e. one is dominant and the other is suppressed.
Homozygous (homos - identical, zygote - paired) organism with identical structures of a given type. Both dominant or both recessive. And in heterozygous organisms both traits are present - dominant and recessive.
Homozygous organisms are those organisms that have two identical gene forms (either both dominant or both recessive);
Heterozygous organisms are those organisms that have both dominant and recessive forms of genes.
Homozygous organisms do not have segregation of characters, but heterozygous ones do.
There are dominant genes and recessive ones (weakly influencing).
Dominant genes are designated by a capital English letter, for example A, and recessive - lowercase a.
In heterozygous organisms, usually one gene is dominant and the second is recessive:
It is designated as follows: Aa.
When a given organism creates offspring, the dominant gene plays a decisive role in what kind of offspring it will be, that is A.
For example, if we consider mice. If the dominant gene A is a fluffy coat, and recessive a- is bald (there are bald albinos), then the dominant gene will win A and the descendant will be hairy. Moreover, this will also lead to an increase in the genus, since bald individuals are not protected from the cold and will most likely die, while hairy ones will be able to survive until they grow up and leave offspring.
Homozygous organisms are those organisms that have the same genes (alleles). Or two recessive aa, or two dominant A.A..
