Homozygous trait. Allelic genes, their properties. Homozygotes and heterozygotes

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:

1. Different traits are encoded by different genes;
2. Constancy - in the absence of a mutating effect, the hereditary material is transmitted unchanged;
3. Lability – the ability to succumb to mutations;
4. Specificity - a gene carries special information;
5. Pleiotropy – one gene encodes several traits;

Subject to conditions external environment genotype produces 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.

Exist 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 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 the presence of the same alleles on both chromosomes (AA, bb). In homozygous organisms they code for the same traits (e.g. White color 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, a – 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 from parents ( dark hair) is three times higher than recessive.

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 And smooth surface seeds, and recessive - 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)

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 most significant properties of any living organism is heredity, which underlies evolutionary processes on the planet, as well as the preservation of species diversity on it. The smallest unit of heredity is the gene, a structural element responsible for the transmission of hereditary information associated with a particular trait of the organism. Depending on the degree of manifestation, dominant and Characteristic feature dominant units is the ability to “suppress” recessive ones, having a decisive effect on the body, not allowing them to manifest themselves in the first generation. However, it is worth noting that along with incomplete, in which it is not able to completely suppress the manifestation of recessive and overdominance, which involves the manifestation of the corresponding characteristics in a form stronger than in homozygous organisms. Depending on which allelic (that is, responsible for the development of the same trait) genes it receives from the parental individuals, heterozygous and homozygous organisms are distinguished.

Determination of a homozygous organism

Homozygous organisms are objects of living nature that have two identical (dominant or recessive) genes for one or another trait. Distinctive feature subsequent generations of homozygous individuals is their lack of splitting of characters and their uniformity. This is explained mainly by the fact that the genotype of a homozygous organism contains only one type of gametes, designated if we're talking about o and lowercase when mentioning recessives. Heterozygous organisms differ in that they contain different allelic genes, and, in accordance with this, form two different types gametes. Homozygous organisms that are recessive for major alleles can be designated as aa, bb, aabb, etc. Accordingly, homozygous organisms with dominant alleles have the code AA, BB, AABB.

Patterns of inheritance

Crossing two heterozygous organisms, the genotypes of which can be conventionally designated as Aa (where A is a dominant and a is a recessive gene), provides the opportunity to obtain, with equal probability, four different combinations of gametes (genotype variant) with a 3:1 split in phenotype. In this case, the genotype is understood as the set of genes that the diploid set of a particular cell contains; under the phenotype - a system of external, as well as internal signs the organism in question.

and its features

Let us consider the patterns associated with crossing processes in which homozygous organisms take part. In the same case, if a dihybrid or polyhybrid crossing takes place, regardless of the nature of the inherited traits, splitting occurs in a ratio of 3:1, and this law is valid for any number of them. Crossing of second generation individuals in this case forms four main types of phenotypes with a ratio of 9:3:3:1. It is worth noting that this law is valid for homologous pairs of chromosomes, the interaction of genes within which does not occur.

Represented by different alleles. When they say that given organism heterozygous(or heterozygous for gene X), this means that the copies of genes (or a given gene) on each of the homologous chromosomes are slightly different from each other.

In heterozygous individuals, based on each allele, slightly different variants of the protein (or transport or ribosomal RNA) encoded by this gene are synthesized. As a result, a mixture of these variants appears in the body. If the effect of only one of them is externally manifested, then such an allele is called dominant, and the one whose effect does not receive external expression is called recessive. Traditionally, when schematically depicting a cross, the dominant allele is designated capital letter, and recessive is lowercase (for example, A And a). Sometimes other designations are used, such as an abbreviated gene name with plus and minus signs.

With complete dominance (as in Mendel's classic experiments with the inheritance of the pea shape), a heterozygous individual looks like a dominant homozygote. When homozygous plants with smooth peas (AA) are crossed with homozygous plants with wrinkled peas (aa), the heterozygous offspring (Aa) have smooth peas.

With incomplete dominance, an intermediate variant is observed (as with the inheritance of the color of the corolla of flowers in many plants). For example, when crossing homozygous red carnations (RR) with homozygous white ones (rr), the heterozygous offspring (Rr) have pink corollas.

If external manifestations represent a mixture of the effects of both alleles, as in the inheritance of blood groups in humans, then they speak of codominance.

It should be noted that the concepts of dominance and recessiveness were formulated within the framework of classical genetics, and their explanation from the standpoint of molecular genetics encounters certain terminological and conceptual difficulties.

see also

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• Chained Knights (film)
• Kondylos

See what “Heterozygote” is in other dictionaries:

heterozygote- heterozygote... Spelling dictionary-reference book

HETEROSYGOTE- (from hetero... and zygote), a cell or organism in which homologous (paired) chromosomes carry different shapes(alleles) of a particular gene. As a rule, it is a consequence of the sexual process (one of the alleles is introduced by the egg, and the other ... ... Modern encyclopedia

HETEROSYGOTE- (from hetero... and zygote) a cell or organism in which homologous chromosomes carry different forms (alleles) of a particular gene. Wed. Homozygote... Big Encyclopedic Dictionary

HETEROSYGOTE- HETEROSYGOTE, an organism that has two contrasting forms (ALLELES) of a GENE in a pair of CHROMOSOMES. In cases where one of the forms is DOMINANT and the other is only recessive, the dominant form is expressed in the PHENOTYPE. see also HOMOZYGOTE... Scientific and technical encyclopedic Dictionary

HETEROSYGOTE- (from hetero... and zygote), an organism (cell) in which homologous chromosomes carry different. alleles (alternative forms) of a particular gene. Heterozygosity, as a rule, determines the high viability of organisms, good adaptability... Biological encyclopedic dictionary

heterozygote- noun, number of synonyms: 3 zygote (8) transheterozygote (1) cisheterozygote ... Synonym dictionary

heterozygote- An organism that has different alleles at one or more specific locus Biotechnology Topics EN heterozygote ... Technical Translator's Guide

heterozygote- (from hetero... and zygote), a cell or organism in which homologous chromosomes carry different forms (alleles) of a particular gene. Wed. Homozygote. * * * HETEROSYGOTE HETEROSYGOTE (from hetero and zygote (see ZYGOTE)), a cell or organism in which ... ... encyclopedic Dictionary

heterozygote- heterozygote heterozygote. An organism in a state of heterozygosity . (

Gregor Mendel was the first to establish the fact that plants similar in appearance, may differ sharply in hereditary properties. Individuals that do not split in the next generation are called homozygous. Individuals whose offspring exhibit splitting of characters are called heterozygous.

Homozygosity - this is a state of the hereditary apparatus of an organism in which homologous chromosomes have the same form of a given gene. The transition of a gene to a homozygous state leads to the manifestation of recessive alleles in the structure and function of the body (phenotype), the effect of which, in heterozygosity, is suppressed by dominant alleles. The test for homozygosity is the absence of cleavage at certain types crossing. A homozygous organism produces for this gene only one type of gamete.

Heterozygosity - this is inherent in everyone hybrid organism a condition in which its homologous chromosomes carry different forms (alleles) of a particular gene or differ in the relative arrangement of genes. The term “Heterozygosity” was first introduced by the English geneticist W. Bateson in 1902. Heterozygosity occurs when gametes of different genetic or structural composition merge into a heterozygote. Structural heterozygosity occurs when a chromosomal rearrangement of one of the homologous chromosomes occurs; it can be found in meiosis or mitosis. Heterozygosity is revealed using test crossing. Heterozygosity is usually - consequence of the sexual process, but can arise as a result of mutation. With heterozygosity, the effect of harmful and lethal recessive alleles is suppressed by the presence of the corresponding dominant allele and appears only when this gene transitions to a homozygous state. Therefore, heterozygosity is widespread in natural populations and is, apparently, one of the causes of heterosis. The masking effect of dominant alleles in heterozygosity is the reason for the persistence and spread of harmful recessive alleles in the population (the so-called heterozygous carriage). Their identification (for example, by testing sires by offspring) is carried out during any breeding and selection work, as well as when making medical and genetic forecasts.

In breeding practice, the homozygous state of genes is called " correct". If both alleles controlling a characteristic are the same, then the animal is called homozygous, and in breeding, this characteristic will be inherited. If one allele is dominant and the other is recessive, then the animal is called heterozygous, and outwardly will demonstrate a dominant characteristic, and by inheritance pass on either a dominant characteristic or a recessive one.

Any living organism has a section of DNA (deoxyribonucleic acid) molecules called chromosomes. During reproduction, germ cells copy hereditary information by their carriers (genes), which make up a section of chromosomes that have the shape of a spiral and are located inside the cells. Genes located in the same loci (strictly defined positions in the chromosome) of homologous chromosomes and determining the development of any trait are called allelic. In a diploid (double, somatic) set, two homologous (identical) chromosomes and, accordingly, two genes carry the development of these various signs. When one characteristic predominates over another it is called dominance, and genes dominant. A trait whose manifestation is suppressed is called recessive. Homozygosity allele is called the presence in it of two identical genes (carriers of hereditary information): either two dominant or two recessive. Heterozygosity allele is called the presence of two different genes in it, i.e. one of them is dominant and the other is recessive. Alleles that in a heterozygote give the same manifestation of any hereditary trait as in a homozygote are called dominant. Alleles that manifest their effect only in a homozygote, but are invisible in a heterozygote, or are suppressed by the action of another dominant allele, are called recessive.

Genotype - the totality of all the genes of an organism. A genotype is a collection of genes that interact with each other and influence each other. Each gene is influenced by other genes of the genotype and itself influences them, so the same gene can manifest itself differently in different genotypes.

Phenotype – the totality of all properties and characteristics of an organism. The phenotype develops on the basis of a specific genotype as a result of the interaction of the organism with conditions environment. Organisms that have the same genotype may differ from each other depending on the conditions of development and existence.

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 individual development 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 will show 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 one to trace the patterns of inheritance of traits in a series 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.

In a monohybrid crossing of homozygous individuals having different meanings alternative traits, 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. Determination of heterozygosity for recessive alleles that cause hereditary diseases(i.e. identifying carriers of this disease) - important problem honey. 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 characteristics are understood as different meanings any sign, for example, the sign is the color of peas, alternative signs are yellow color, 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 heterozygotes are bred, they are lost in the offspring. valuable properties varieties and breeds precisely because their sex cells are heterogeneous. Yellow color (A) and smooth shape (B) of seeds are dominant characteristics, green color(a) and wrinkled form (b) are recessive traits.