What does genotype mean? What are genotypes? The significance of the genotype in the scientific and educational spheres IV. Homework
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Genetics has repeatedly amazed us with its achievements in the field of studying the genome of humans and other living organisms. The simplest manipulations and calculations cannot do without generally accepted concepts and signs, which this science is not deprived of.
What are genotypes?
The term refers to the totality of genes of one organism, which are stored in the chromosomes of each of its cells. The concept of genotype should be distinguished from genome, since both words have different lexical meanings. Thus, the genome represents absolutely all the genes of a given species (human genome, monkey genome, rabbit genome).
How is a person's genotype formed?
What is a genotype in biology? Initially, it was assumed that the set of genes of each cell in the body is different. This idea was refuted from the moment scientists discovered the mechanism of formation of a zygote from two gametes: male and female. Since any living organism is formed from a zygote through numerous divisions, it is not difficult to guess that all subsequent cells will have exactly the same set of genes.
However, it is necessary to distinguish the genotype of the parents from that of the child. The fetus in the womb has half the set of genes from mom and dad, so although children are similar to their parents, at the same time they are not 100% copies of them.
What are genotype and phenotype? What is their difference?
Phenotype is the totality of all external and internal characteristics of an organism. Examples include hair color, presence of freckles, height, blood type, amount of hemoglobin, synthesis or absence of an enzyme.
However, the phenotype is not something definite and constant. If you observe hares, the color of their fur changes depending on the season: in summer they are gray and in winter white.
This phenomenon is explained by the fact that during the differentiation of embryonic cells, some genes are turned on, while others are in “sleep mode”. The latter either remain inactive throughout their lives or are reused by the cell in stressful situations.
Examples of recording genotypes
In practice, the study of hereditary information is carried out using conditional encryption of genes. For example, the gene for brown eyes is written with a capital letter “A”, and the manifestation of blue eyes is written with a small letter “a”. This shows that the trait of brown eyes is dominant, and blue eyes are recessive.
So, based on the characteristics, people can be:
dominant homozygotes (AA, brown-eyed); heterozygotes (Aa, brown-eyed); recessive homozygotes (aa, blue-eyed).
Using this principle, the interaction of genes with each other is studied, and usually several pairs of genes are used at once. This raises the question: what is genotype 3 (4/5/6, etc.)?
This phrase means that three pairs of genes are taken at once. The entry will be, for example, like this: АаВВСс. Here new genes appear that are responsible for completely different characteristics (for example, straight hair and curls, the presence of protein or its absence).
Why is the typical genotype record arbitrary?
Any gene discovered by scientists has a specific name. Most often these are English terms or phrases that can reach considerable lengths. The spelling of names is difficult for representatives of foreign science, so scientists have introduced a simpler recording of genes.
Even a high school student can sometimes know what genotype 3a is. This notation means that a gene is responsible for 3 alleles of the same gene. If the real gene name were used, understanding the principles of heredity might be difficult.
If we are talking about laboratories where serious karyotype research and DNA studies are carried out, then they resort to the official names of genes. This is especially true for those scientists who publish the results of their research. 
Where are genotypes used?
Another positive feature of using simple notation is its versatility. Thousands of genes have their own unique name, but each of them can be represented by just one letter of the Latin alphabet. In the overwhelming majority of cases, when solving genetic problems for various traits, the letters are repeated again and again, and the meaning is deciphered each time. For example, in one problem, gene B is the color of black hair, and in another, it is the presence of a mole.
The question “what are genotypes” is raised not only in biology classes. In fact, the convention of designations causes the vagueness of formulations and terms in science. Roughly speaking, the use of genotypes is a mathematical model. In real life, everything is more complicated, despite the fact that the general principle was nevertheless transferred to paper.
By and large, genotypes in the form in which we know them are used in school and university education programs when solving problems. This simplifies the understanding of the topic “what are genotypes” and develops students’ ability to analyze. In the future, the skill of using such a notation will also be useful, but for real research, real terms and gene names are more appropriate.
The genes are currently being studied in various biological laboratories. Encryption and use of genotypes is relevant for medical consultations when one or more characteristics can be traced over a number of generations. As a result, experts can predict the phenotypic manifestation in children with a certain degree of probability (for example, the appearance of blond hair in 25% of cases or the birth of 5% of children with polydactyly).
Genotypes of the hepatitis C virus are strains - different variants of the causative agents of the disease. The classification of main types includes six groups, which for convenience are usually designated by numbers. However, each specific species has its own subspecies. Thus, the total number of genotypes increases to eleven. In turn, some subspecies are divided into quasi-species.
For treatment to be effective, it is very important to correctly determine which of the available types the hepatitis virus belongs to.
By the way, it is worth explaining to the average person that determining the genotype of a virus in medical language sounds like genotyping. A person, in principle, can be infected with a virus containing only one specific genotype, but as mentioned above, each subspecies is divided into several viruses that are similar in nature, which are called quasi-species.
Many of them can mutate (change), which significantly complicates the chosen treatment tactics. Note that the complexity of treating some diseases, in particular chronic jaundice, is due to this factor.
General information about the virus
The liver performs various tasks in the human body. This body can be called a kind of record holder for the total number of important functions performed. Viral hepatitis can cause various changes in all parameters determined by laboratory testing. True, some of the changes are not specific - they can also occur with other infections.
But there are also signs that are typical only for viral hepatitis. Basically, these changes affect liver cells and destroy them. This, in turn, leads to the release into the blood of a large number of enzymes that are found in hepatocytes (liver cells are called hepatocytes).
In medicine, there is such a thing as a flavivirus. So, the hepatitis C virus belongs to this family.
It is impossible to examine, let alone make an image of, this virus due to the fact that its content in the blood of an infected person is negligible. In the environment, flaviviruses can survive for a very short period of time; they are very unstable. The incubation period for hepatitis C lasts from three weeks to 120 days.
The virus can combine with other viruses, and it can mutate, which does not have the best effect on the patient’s well-being and complicates treatment. It should be noted that hepatitis can lead to serious diseases - the formation of a low-quality tumor and cirrhosis.
Methods of transmission of the virus
The genotypes of a disease such as hepatitis C depend on two main factors - a person’s lifestyle and place of residence according to geographic location. It has been noted that throughout the world, people are being infected with a separate type of virus, characteristic and predominant in this particular territory.
In order to understand the diversity of genotypes, you should look at the description of the most common ones.
Explanation: the number is the genotype, and the letter index is the subspecies of the virus:
1a, 1b, 1c; 2a, 2b, 2c, 2d; 3a, 3b, 3c, 3d, 3e, 3f; 4a, 4b, 4c, 4d, 4e, 4f, 4g, 4h, 4i, 4j; 5a.
Experts around the world carry out genotyping and, based on these studies, state that, for example, in our country, as well as in neighboring territories - Ukraine, the Republic of Belarus, viruses of genotype 1, 2, 3 are more common.
If we consider the subspecies, then in the countries of the former Soviet Union genotype 1b predominates. Doctors note that this subtype is difficult to treat, based on taking drugs containing interferon. Only after pharmaceutical companies provided a new generation of medicine, and doctors changed the treatment regimen (interferon is no longer used), did the effectiveness of therapy noticeably improve.
A fifth of the population is diagnosed with genotype 3a, and therefore situations where infection with a similar virus can occur will be discussed below:
people who use drugs are at increased risk (the method of transmission of the virus is an unsterile needle); During sexual intercourse, the infection can also enter the body of a healthy person; the virus is transmitted to humans through blood, which means that infection can occur during blood transfusion; A dental office or other hospital setting where medical instruments are not properly disinfected are the most dangerous places in terms of transmission of infection. when visiting a nail salon - non-sterile instruments; tattoos and ear piercings or piercings can lead to infection.
During pregnancy, infection of the fetus from an infected mother can also occur.
This disease is asymptomatic for a long time. And only when the disease reaches an advanced stage, the patient may notice characteristic signs - nausea, weakness, unstable stools, weight loss, lack of appetite, yellowish discoloration of the skin and mucous membranes. This is the insidiousness of this disease, and perhaps for this reason hepatitis C is called the “soft-pawed killer.”
The disease in most cases becomes chronic, and in a third of the total number of infected people, the virus can cause cirrhosis of the liver.
Thus, people infected with genotype 3a virus often develop steatosis, a disease in which liver cells are destroyed.
Correctly determining the genotype of the virus is a priority for doctors before prescribing treatment to a patient. Therefore, clinics carry out genotyping, and then, based on the data obtained, they make a decision on an effective treatment method for the patient.
Diagnostic methods
In our country, an experimental technology for detecting viruses is used, which is called PCR diagnostics. This type of analysis can significantly increase the concentration of viral DNA or RNA enzymes in selected samples. Such actions make it possible to reliably recognize and also identify a quantitative indicator of viruses contained in test tubes.
Modern diagnostic methods make it possible to identify infected people in the early stages of the disease in 97% of cases.
Analysis tests may be positive, negative or neutral. In the latter option, the patient will be advised to undergo the examination again.
In order to confirm or refute the presence of infection in a person’s blood, a qualitative PCR analysis is performed. Samples for analysis are taken from people in whose blood antibodies to hepatitis were detected as a result of laboratory tests. Based on the test results, medical workers can give only two results - “detected” and “not detected.”
If the patient was given a result with the wording “detected,” then this only means that a virus was detected in the person’s blood, which means that infection has occurred. Accordingly, another wording - “not detected” indicates that no RNA fragments were found in the submitted biological material, and this may mean that the patient is healthy or the concentration in the selected sample is so low that it is not possible to make a qualitative analysis.
In the acute stage of hepatitis C, using the PCR diagnostic method, RNA can be determined 10 days after infection. In this case, the disease will be identified in the early stages, which means there is a high probability that the person will be cured.
Identification of certain types of hepatitis causative agent in a patient cannot lead to a diagnosis in terms of its complexity and stage of the disease. The analysis only shows which virus was detected in the blood.
The patient must undergo a comprehensive laboratory examination. Only in this case, the doctor will be able, after assessing the entire situation, to diagnose the patient and accordingly decide on the choice of treatment, as well as predict the further development of the clinical picture of the disease.
What is "Genotype" and what does it mean? Meaning and interpretation of the term in dictionaries and encyclopedias:
Sexological dictionary » Genotype
the genetic constitution of an organism, the totality of all hereditary inclinations inherent in a given individual.
(from the Greek genos - origin + typos - form, pattern) - the totality of all genes of a given cell or organism; in other words, it is the totality of hereditary inclinations; term and concept "G." (and also “gene”) was introduced by the Danish botanist V. L. Johansen (1909). Amer. geneticist T. H. Morgan showed that genes are located on chromosomes, creating the chromosomal theory of heredity (1912). Syn. genome. Genes are made up of deoxyribonucleic acid (DNA) molecules; DNA molecules, as proven in 1953 by English. biophysicists James Watson and Francis Crick (based on X-ray photographs of M. Wilkins and R. Franklin), have a special spatial structure, visualized in the form of the famous “double helix” model (for this discovery Watson, Crick and Wilkins received the Nobel Prize in 1962) . The human genome contains approx. 50,000-100,000 structural genes encoding protein molecules (structural proteins and enzymes). The place that a gene occupies in a chromosome is called a locus. G. at this locus is called that specific pair of alleles (gene variants) that are represented in the homologous chromosomes of an individual (for example, genotypes AA, Aa or aa). The set of genes of a given population (as a whole or for a certain locus) is called the gene pool. See Behavioral Genetics, Psychogenetics, Phenotype. (B.M.)
Psychological encyclopedia » Genotype
(from the Greek genos - origin, typos - form, sample) - a set of characteristics of an individual that can be interpreted as a manifestation of genetic, hereditary factors.
(from the Greek genos - clan, tribe, origin and typos - image) - English. genotype; German Genotyp. The totality of all the genes of a given organism, the hereditary constitution that determines the totality of the properties of a given individual at a certain stage of development (phenotype).
Big Encyclopedic Dictionary » Genotype
(from gene and type) - the genetic (hereditary) constitution of an organism, the totality of all its genes. In modern genetics, it is considered not as a mechanical set of independently functioning genes, but as a single system in which any gene can be in complex interaction with other genes. See also Phenotype.
Psychological Dictionary » Genotype
(Greek genos - origin, typos - form, sample) - a set of genes or any qualities received by a person as an inheritance from his parents.
Psychological Dictionary » Genotype
The genetic constitution of an organism, the totality of all hereditary inclinations inherent in a given individual.
Psychological Dictionary » Genotype
Word formation. Comes from the Greek. genos - origin + typos - form, pattern. Category. A set of characteristics of an individual that are manifestations of genetic, hereditary factors.
Psychological Dictionary » Genotype
genetic design of an individual's body.
Psychological Dictionary » Genotype
Genetic composition of personality. is a collection of inherited genetic material that is passed on from generation to generation. Although this material is inherited, it does not necessarily manifest itself in the phenotype of the organism. Thus, genotype is best viewed as a series of natural factors that influence the development of an organism, but do not control that development.
Psychological Dictionary » Genotype
(Greek genos - genus, origin, typos - imprint, form, sample). A set of hereditary factors of an organism that, in interaction with the environment, determine the formation of a phenotype. G. is judged by its manifestations in the phenotype. The study of G. seems important in medical genetic counseling. Thus, the risk of developing schizophrenia, among other factors, depends on the proximity of the parents’ genotypes.
Psychological Dictionary » Genotype
Genetic constitution, the totality of genes of a given organism, received from its parents. Each type of microorganism, plant and animal has a characteristic genotype. However, within each species, organisms differ in their genotypes. In humans, only monozygotic (identical) twins have identical genotypes (-> psychogenetic method). According to I.P. Pavlov - an innate type of nervous system. This concept is related to the concept of temperament.
Psychological Dictionary » Genotype
1. The genetic structure of an individual organism, the specific set of genes that it carries. includes hereditary factors that can be passed on to future generations even if they are not expressed in the individual: see phenotype. The use of the term in this meaning, especially in developmental psychology research, usually involves a focus on the idea of genotype as a set of hereditary factors influencing the development of an individual. The term does not refer directly to heritable traits, but essentially to hereditary influences that contribute to the development of certain traits. This value reflects the complexity of the interaction between heredity and environment and the recognition that a given genotype can be expressed in a range of phenotypes. 2. In K. Lewin’s personality theory, there is a complete set of reasons responsible for any behavioral phenomenon. The term is used more often in this meaning than in meaning 1, and is now rarely seen.
Psychological Dictionary » Genotype
(genotype) - 1. The genetic make-up of a person or group of people, which is determined by their characteristic set of genes. 2. Genetic information contained in a pair of alleles that determine any characteristic feature of a person. 3. A gene or pattern of genes of which the exact details are determined. 4. The set of genes localized in its chromosomes (ed.). For comparison: Phenotype.
Sociological Dictionary » Genotype
biological, or naturally determined, characteristics of an organism.
Sociological Dictionary » Genotype
(genotype) is a unique combination of genes that an individual receives from both parents as a result of cell division (meiosis) and the fusion of an egg and sperm (fertilization). All of these genes have the potential to determine or help determine the characteristics of an individual, but not all actually exert influence because they are derived from both the parents and the gene (for example, the eye color of one parent may dominate the eye color of the other). , therefore, expresses genetic potential and, even if the genes cannot be expressed in an individual, they will be passed on through inheritance. While the genotype is the overall genetic potential of an individual, the phenotype is the actual expression of the individual's genes and thus describes the pattern of genes that influenced its development (for example, a gene for an individual's eye color, but not for an eye color not expressed, although all still contained in the genotype).
Philosophical Dictionary » Genotype
The hereditary basis of a biological organism, the complete set of its genes.
Philosophical Dictionary » Genotype
a unique combination of genes that an individual receives from both parents as a result of cell division (meiosis) and the fusion of an egg and sperm (fertilization). All of these genes have the potential to determine or help determine the characteristics of an individual, but not all actually exert influence because they are derived from both the parents and the gene (for example, the eye color of one parent may dominate the eye color of the other). , therefore, expresses genetic potential and, even if the genes cannot be expressed in an individual, they will be passed on through inheritance. While the genotype is the overall genetic potential of an individual, the phenotype is the actual expression of the individual's genes and thus describes the pattern of genes that influenced its development (for example, a gene for an individual's eye color, but not for an eye color that was not expressed, although all still contained in the genotype).
Sample solution to a problem
to determine the genotype and phenotype of the parents
by genotype and phenotype of descendants
Task: Normal hearing in humans is determined by a dominant gene A, and hereditary deaf-mutism is determined by a recessive gene A. From the marriage of a deaf-mute woman with a normal man, a deaf-mute child was born. Determine the genotypes of the parents.
Progress of solving the problem:
1. Let's briefly write down the conditions of the problem:
Given:
A- normal hearing
A- deaf-mute
Genotype P - ?
2. We determine the genotypes of the parents.
According to the conditions of the problem, the woman is deaf and mute, she has a phenotypically manifested recessive trait, therefore her genotype is unambiguous - ah. A man with normal hearing, he has a phenotypically manifested dominant trait. An organism that exhibits a dominant trait may have two variants of the genotype - AA or ahh. Since, according to the conditions of the problem, it is impossible to accurately determine the genotype of the paternal organism, but knowing that it contains a dominant gene, we write its genotype as A - .
3. We write down the crossing scheme:
Solution:
R♀ aa × ♂ A -
4. Under the genotype we sign the phenotype:
R♀ aa × ♂ A -
deaf and dumb normal. hearing
5. We record the genotype and phenotype of the offspringF1 :
The offspring included a deaf-mute child. He has a phenotypically manifested recessive trait, so his genotype is unambiguous - ahh.
R♀ aa × ♂ A -
deaf and dumb normal. hearing
deaf-mute
6. We analyze the genotypes of parents and offspring.
Ahh .
7. We rewrite the crossing scheme using the established genotypes of the parents:
R♀ aa × ♂ A a
deaf and dumb normal. hearing
8. We write down the types of gametes of the parents:
R♀ aa × ♂ A a
deaf and dumb normal. hearing
9. Getting descendantsF1 :
F 1 ahh Ahh
deaf and dumb normal. hearing
10. We carry out a crossbreeding analysis:
In F1, a 1:1 split occurred. This splitting is obtained by crossing a heterozygous individual with an individual homozygous for a recessive trait. Therefore, the genotypes of the parents we established are correct.
Brief description of the solution to the problem:
R♀ aa × ♂ A -
deaf and dumb normal. hearing
deaf-mute
Knowing that each F1 individual receives one gene from the maternal organism and one gene from the paternal organism, it is clear that it received a recessive gene from the paternal organism. Therefore, the genotype ♂ is Ahh .
R♀ aa × ♂ A a
deaf and dumb normal. hearing
F 1 ahh Ahh
deaf and dumb normal. hearing
By genotype: 1( Ahh) : 1(ahh)
Aa - heterozygous organism
aa - homozygous organism for a recessive gene.
By phenotype: 1: 1 (50% or 1/2 deaf and mute: 50% or 1/2 with normal hearing).
Answer: genotype ♀- aa, ♂- Aa.
Let's consider G. Mendel's reasoning using the terms described above. A biallelic gene is responsible for the shape of pea seeds. We denote its dominant allele (phenotype - smooth seeds) as A, and recessive as a(shriveled seeds). The genotype is determined by a pair of alleles. There are three possible genotypes: A.A., Aa,aa. Genotype Aa called heterozygous, and genotypes A.A., aa -homozygous. Since the allele A is dominant, then plants of the first two genotypes will have smooth seeds, and the third will have wrinkled seeds.
At the first stage of his experiment, G. Mendel took homozygous plants A.A., aa. The first type produced gametes having the allele A, the second corresponded to gametes with the allele a.
Crossing homozygous plants A.A. And aa(fusion of gametes A And a) produces a heterozygous plant Aa. The latter produces gametes carrying the alleles A And a. Which of the two alleles a particular gamete will receive is a matter of chance and the probability of each event is 1/2.
At the second stage of G. Mendel's experiment, heterozygous plants were crossed. Genotype A.A. occurs in a descendant if each of the parents passed on a gamete with the allele A. Events are independent. Probability P(AA) descendant with genotype A.A. equal to 1/4. Likewise, the probability P(aa) appearance of a descendant aa also 1/4. The probability of producing an offspring with the genotype Aa can be calculated by addition: P(Aa)=1-1/4-1/4=1/2. The probability that a plant offspring of two heterozygous parents will have smooth seeds is: P(AA)+P(Aa)=1/4+1/2=3/4. Wrinkled seeds are likely to be observed P(aa)=1/4.
This is the mathematical model that explains the experiments of G. Mendel. Let's discuss the question of its adequacy. Let us recall that in experiments the corresponding frequencies were observed approximately. This is a problem about testing a statistical hypothesis. To check, you can use the criterion Pearson.
Suppose we are observing a series of n independent trials. Each of them can end in one of m outcomes. The probabilities of outcomes do not change from trial to trial. The null hypothesis to be tested is that these probabilities are equal to some predetermined numbers: . Relative to the number n is assumed. that it is big enough. Let be the empirical frequencies of the outcome obtained as a result of experience. The amount is calculated:
,
which is often called the Pearson sum. It turns out that as n increases, the distribution of statistics S tends to a limiting distribution with m-1 degrees of freedom, independent of n and numbers. For any 0 you can specify a practical limit 
such that
.
In other words, inequality 
almost impossible. The number is called the significance level.
Let's set the significance level =0.05, which is very popular in biology. In the case under consideration, the number of degrees of freedom is m-1=1. The distribution of the Pearson sum for such a large number as n=7,324 is practically no different from the distribution with one degree of freedom. We determine from the tables 
3.84. Let's calculate the Pearson sum:
Since the Pearson sum is less 
, then the null hypothesis agrees well with the experimental results. We have good reasons to believe that Mendel's law is true.
In genetics, a certain formalism has been developed that allows one to quickly derive patterns. Allelic pairs are presented as:
, 
, 
,
Crossing of genotypes is indicated by the "" multiplication sign. Brackets in formulas are expanded according to the usual rules and multiplication signs are omitted. Crossing heterozygous plants is described by the formula:
The resulting formula states that genotypes A.A. And aa arise during crossing with a probability of 1/4, and the genotype Aa with probability 1/2. Since genotypes A.A. And Aa have smooth seeds, then 3/4 of the offspring have smooth seeds, and 1/4 have wrinkled seeds (genotype aa).
Let's solve a simple problem of crossing genotypes Aa And aa:
Thus, half of the genotypes will be heterozygous and half homozygous.
Most genotype traits are controlled by more than two alleles. Such alleles are called multiple. Such alleles in any unpaired combination can be found in any cell, since only two alleles of one gene can be simultaneously present in the genotype. Such genotypes are called diploid. Genes that control blood groups are polyallelic. A person’s blood type depends on the presence or absence of specific proteins in red blood cells ( A And B). There are four blood types: Blood type A with genotypes A.A. And A.O.(blood type contains protein A), blood type B with genotypes BB And B.O.(contains protein B), Blood type AB(contains both proteins), blood type O.O.(lack of proteins A And B). Thus, blood type is controlled by three alleles A, B, O one gene. Alleles A And B- dominant in relation to O. In the presence of alleles A And B there is no dominance. Thus, blood groups are determined by six genotypes A.A.,A.O.,AB,BB,B.O.,O.O..
LABORATORY WORK No. 6
Formatting tasks on genetics
| ♀ | female body |
| ♂ | male body |
| × | crossing sign |
| P | parent organisms |
| F 1, F 2 | |
| A, B, C... | |
| a, b, c... | |
| AA, BB, SS... | |
| Aa, Bb, Ss... | |
| aa, bb, ss... | genotypes of recessive individuals |
| AaBb, AaBbCc | |
| AB,CD ab cd | |
| A, a, AB, cd | gametes |
Example.
Solution
A – normal pigmentation,
a – albinism.
R ♀() × ♂()
Normal
albino pigmentation
F 1 aa A*
albino normal
pigmentation
R♀A* × ♂aa
normal albino
F 1 A* aa
normal albino
P ♀Aa × ♂aa
normal albino
gametes: A a a
F 1 Aa aa
normal albino
Monohybrid cross
Example.
A – black color gene,
a – red color gene.
AA (25%), Ahh(50%) and ahh
Crossing scheme
P ♀aa × ♂AA
red black
gametes a A
100% black
F 1 ♀Aa × ♂Aa
black black
gametes A a A a
75% black 25% red
Answer:
№1-1
№1-2
Task 2. Solve the problems and write down the solution diagram in your notebook.
№2-1. In guinea pigs, the shaggy coat gene (R) is dominant over the smooth coat gene (r). A shaggy pig, when crossed with a smooth one, produced 18 shaggy and 20 smooth offspring. What is the genotype of the parents and offspring? Could these pigs produce only smooth pigs?
№2-2. In oats, early ripeness dominates over late ripeness. On the experimental site, crossing late-ripening oats with heterozygous early-ripening oats resulted in 69,134 early-ripening plants. Determine the number of late-ripening plants.
Task No. 3. Solve the problems and write down the solution diagram in your notebook.
№3-1 . Phenylketonuria (a disorder of amino acid metabolism) is inherited as a recessive trait. The wife is heterozygous for the phenylketonuria gene, and the husband is homozygous for the normal allele of this gene. What is the probability of them having a sick child?
№3-2. Irish Setters can be blind as a result of a recessive gene. A pair of animals with normal vision produced a litter of several puppies, one of which turned out to be blind. Determine the genotypes of the parents. One of the sighted puppies from this litter must be sold for further breeding. What is the probability that he is heterozygous for the blindness gene?
Task No. 4. Solve the problems and write down the solution diagram in your notebook.
№ 4-1. Datura, which has purple flowers, produced 30 offspring with purple and 9 with white flowers during self-pollination. What conclusions can be drawn about the inheritance of flower color in plants of this species? What part of the F 1 progeny will not produce segregation during self-pollination?
№ 4-2. When gray flies were crossed with each other, segregation was observed in their F 1 offspring. 1392 individuals were gray and 467 individuals were black. Which trait is dominant? Determine the genotypes of the parents.
Task No. 5. Solve the problems and write down the solution diagram in your notebook.
№ 5-1. In the “night beauty” plant, the inheritance of flower color is carried out according to an intermediate type. Homozygous organisms have red or white flowers, while heterozygotes have pink flowers. When two plants were crossed, half of the hybrids had pink flowers and half had white flowers. Determine the genotypes and phenotypes of the parents.
Task No. 6. Solve the problems and write down the solution diagram in your notebook.
№ 6-1. The father has blood type IV, the mother has blood type I. Can a child inherit his father’s blood type?
№ 6-2. Parents have blood groups II and III. What groups should be expected in the offspring?
LABORATORY WORK No. 6
Topic: Rules for design and solving problems of monohybrid crossing
Determining the genotypes of individuals unknown by condition is the main methodological operation necessary for solving genetic problems. In this case, the solution should always begin with individuals carrying a recessive trait, since they are homozygous and their genotype for this trait is unambiguous - aa.
Determining the genotype of an organism carrying a dominant trait is a more difficult problem because it can be homozygous (AA) or heterozygous (Aa).
Formatting tasks on genetics
When completing tasks, you must be able to use the symbols accepted in traditional genetics and given below:
| ♀ | female body |
| ♂ | male body |
| × | crossing sign |
| P | parent organisms |
| F 1, F 2 | daughter organisms of the first and second generation |
| A, B, C... | genes encoding dominant traits |
| a, b, c... | allelic genes encoding recessive traits |
| AA, BB, SS... | genotypes of individuals monomozygous for a dominant trait |
| Aa, Bb, Ss... | genotypes of monoheterozygous individuals |
| aa, bb, ss... | genotypes of recessive individuals |
| AaBb, AaBbCc | genotypes of di- and triheterozygotes |
| AB,CD ab cd | genotypes of diheterozygotes in chromosomal form with independent and linked inheritance |
| A, a, AB, cd | gametes |
An example of recording a crossing (marriage) scheme. A – yellow color of seeds, and – green color of seeds.
Rules for solving and formatting problems
Determination of genotypes of organisms by genotypes of parents and offspring:
Example. In humans, albinism is an autosomal recessive trait. An albino man married a woman with normal pigmentation. They had two children - a normal one and an albino one. Determine the genotypes of all specified family members.
Solution
A – normal pigmentation,
a – albinism.
Recording the marriage scheme by phenotype:
R ♀() × ♂()
Normal
albino pigmentation
F 1 aa A*
albino normal
pigmentation
Determining and recording genotypes known from the problem:
The genotype of an individual with a recessive trait is known - aa. An individual with a dominant trait has genotype A*:
R♀A* × ♂aa
normal albino
F 1 A* aa
normal albino
The genotype of an albino man and child is aa, since both of them carry a recessive trait.
A woman and a healthy child have a dominant gene A in their genotype, because they exhibit a dominant trait.
The genotype of a child with normal pigmentation is Aa, since his father is homozygous for a recessive (aa) and could only pass on the a gene to him.
One of the children has the aa genotype. The child receives one allelic gene from the mother, and the other from the father. Therefore, the mother must carry the recessive gene a. Her genotype is Aa.
Recording the progress of reasoning to clarify genotypes and marriage patterns:
P ♀Aa × ♂aa
normal albino
gametes: A a a
F 1 Aa aa
normal albino
Answer: The genotype of the husband is aa, the wife is Aa, the child with normal pigmentation is Aa, the albino child is aa.
Monohybrid cross
Monohybrid is a crossing in which the inheritance of one pair of alternative (contrasting, mutually exclusive) traits determined by one pair of genes is considered. When monohybrid crossing, Mendel's first law (law of uniformity) is observed, according to which when homozygous organisms are crossed, their F 1 descendants exhibit only one alternative trait (dominant), and the second is in a latent (recessive) state. The F 1 offspring are uniform in phenotype and genotype. According to Mendel's second law (the law of segregation), when heterozygotes are crossed, their F2 offspring exhibit segregation by genotype in a ratio of 1:2:1 and by phenotype in a ratio of 3:1. To successfully solve monohybrid crossing problems, it is also necessary to clearly know the rule of “gamete purity”, according to which only one gene from each pair that determines the development of the trait gets into each gamete.
Example. The black color gene in cattle is dominant over the red color gene. What F 1 offspring will be obtained from crossing a purebred black bull with red cows? What kind of F 2 offspring will be obtained from crossing hybrids with each other?
A – black color gene,
a – red color gene.
Red cows carry a recessive trait, therefore, they are homozygous for the recessive gene and their genotype is aa.
The bull carries the dominant trait of black color and is purebred, i.e. homozygous. Therefore, his genotype is AA.
Homozygous individuals produce one type of gamete, so a black bull can only produce gametes carrying the dominant A gene, and red cows only carry the recessive A gene.
They can only be combined in one way, resulting in the formation of a uniform generation F 1 with genotype Aa.
Heterozygotes are equally likely to form gametes containing the A and a genes. Their merging is random, so in F 2 there will be animals with genotypes AA (25%), Ahh(50%) and ahh(25%), that is, individuals with a dominant trait will make up approximately 75%.
Crossing scheme
P ♀aa × ♂AA
red black
gametes a A
100% black
F 1 ♀Aa × ♂Aa
black black
gametes A a A a
75% black 25% red
Answer: When crossing a purebred black bull with red cows, all the offspring will be black. When F 1 hybrids are crossed with each other, splitting will be observed in their offspring (F 2): 3/4 of the individuals will be black, 1/4 will be red.
Determination of the genotypes of organisms based on the genotypes and phenotypes of parents and offspring.
When solving such problems, it is necessary to remember that the genotype of individuals with a recessive trait is known - they are homozygous. The presence of a dominant or recessive gene in organisms carrying a dominant trait (their homo- or heterozygosity) can be determined by the genotypes of their parents or descendants, given that the child receives one gene from each pair from the father, and the second from the mother.
Example. The ability of a person to perceive the bitter taste of phenylthiourea (PTM) is a dominant trait, the gene of which (T) is localized in the 17th autosome. In a family, mother and daughter feel the taste of FTM, but father and son do not. Determine the genotypes of all family members.
Solution
Father and son do not feel the taste of FTM, i.e. carry a recessive trait, therefore, their genotype is tt. Mother and daughter sense taste, which means each of them carries the dominant T gene.
The child receives one chromosome from the father, the other from the mother. From the father, the daughter can only receive the recessive t gene (since it is homozygous). Therefore, the daughter’s genotype is Tt. In the mother's offspring there is an individual with the tt genotype, therefore, she also carries the recessive t gene, and her genotype is Tt.
Marriage scheme:
| R | ♀Tt tastes FTM | × | ♂tt can't taste FTM |
| gametes | T t | t | |
| F 1 | Tt tastes FTM | tt does not taste FTM |
Answer: The genotype of mother and daughter is Tt, father and son are tt.
Task No. 1. Solve the problems and write down the solution diagram in your notebook.
№1-1 . In humans, the gene that causes one of the forms of hereditary deaf-muteness is recessive with respect to the gene for normal hearing. From the marriage of a deaf-mute woman with a normal man, a deaf-mute child was born. Determine the genotypes of all family members.
№1-2 . A gray strand of hair in a person is a dominant sign. Determine the genotypes of parents and children if it is known that the mother has a gray strand of hair, the father does not, and of two children in the family, one has a gray strand and the other does not.
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Genetics has repeatedly amazed us with its achievements in the field of studying the genome of humans and other living organisms. The simplest manipulations and calculations cannot do without generally accepted concepts and signs, which this science is not deprived of.
What are genotypes?
The term refers to the totality of genes of one organism, which are stored in the chromosomes of each of its cells. The concept of genotype should be distinguished from genome, since both words have different lexical meanings. Thus, the genome represents absolutely all the genes of a given species (human genome, monkey genome, rabbit genome).
How is a person's genotype formed?
What is a genotype in biology? Initially, it was assumed that the set of genes of each cell in the body is different. This idea was refuted from the moment scientists discovered the mechanism of formation of a zygote from two gametes: male and female. Since any living organism is formed from a zygote through numerous divisions, it is not difficult to guess that all subsequent cells will have exactly the same set of genes.
However, it is necessary to distinguish the genotype of the parents from that of the child. The fetus in the womb has half the set of genes from mom and dad, so although children are similar to their parents, at the same time they are not 100% copies of them.
Phenotype is the totality of all external and internal characteristics of an organism. Examples include hair color, presence of freckles, height, blood type, amount of hemoglobin, synthesis or absence of an enzyme.
Phenotype is the totality of all external and internal characteristics of an organism. Examples include hair color, presence of freckles, height, blood type, amount of hemoglobin, synthesis or absence of an enzyme.
However, the phenotype is not something definite and constant. If you observe hares, the color of their fur changes depending on the season: in summer they are gray and in winter white.
This phenomenon is explained by the fact that during the differentiation of embryonic cells, some genes are turned on, while others are in “sleep mode”. The latter either remain inactive throughout their lives or are reused by the cell in stressful situations.
Examples of recording genotypes
In practice, the study is carried out using conditional gene encryption. For example, the gene for brown eyes is written with a capital letter “A”, and the manifestation of blue eyes is written with a small letter “a”. This shows that the trait of brown eyes is dominant, and blue is recessive.
So, based on the characteristics, people can be:
- dominant homozygotes (AA, brown-eyed);
- heterozygotes (Aa, brown-eyed);
- recessive homozygotes (aa, blue-eyed).
Using this principle, the interaction of genes with each other is studied, and usually several pairs of genes are used at once. This raises the question: what is genotype 3 (4/5/6, etc.)?
This phrase means that three pairs of genes are taken at once. The entry will be, for example, like this: АаВВСс. Here new genes appear that are responsible for completely different characteristics (for example, straight hair and curls, the presence of protein or its absence).
Why is the typical genotype record arbitrary?
Any gene discovered by scientists has a specific name. Most often these are English terms or phrases that can reach considerable lengths. The spelling of names is difficult for representatives of foreign science, so scientists have introduced a simpler recording of genes.
Even a high school student can sometimes know what genotype 3a is. This notation means that a gene is responsible for 3 alleles of the same gene. If the real gene name were used, understanding the principles of heredity might be difficult.
If we are talking about laboratories where serious karyotype research and DNA studies are carried out, then they resort to the official names of genes. This is especially true for those scientists who publish the results of their research.
Where are genotypes used?
Another positive feature of using simple notation is its versatility. Thousands of genes have their own unique name, but each of them can be represented by just one letter of the Latin alphabet. In the overwhelming majority of cases, when solving genetic problems for various traits, the letters are repeated again and again, and the meaning is deciphered each time. For example, in one problem, gene B is the color of black hair, and in another, it is the presence of a mole.
The question “what are genotypes” is raised not only in biology classes. In fact, the convention of designations causes the vagueness of formulations and terms in science. Roughly speaking, the use of genotypes is a mathematical model. In real life, everything is more complicated, despite the fact that the general principle was nevertheless transferred to paper.
By and large, genotypes in the form in which we know them are used in school and university education programs when solving problems. This simplifies the understanding of the topic “what are genotypes” and develops students’ ability to analyze. In the future, the skill of using such a notation will also be useful, but for real research, real terms and gene names are more appropriate.
The genes are currently being studied in various biological laboratories. Encryption and use of genotypes is relevant for medical consultations when one or more characteristics can be traced over a number of generations. As a result, experts can predict the phenotypic manifestation in children with a certain degree of probability (for example, the appearance of blond hair in 25% of cases or the birth of 5% of children with polydactyly).