GeneticsHeredity and variationThe science that studies the structure, function, variation, transmission and expression of genes.The concept of parent-child in genetics is not limited to parents and children or a family, but also can be extended to include many families. This isPopulation geneticsThe research object of.The concept of parent-child in genetics can also be based on cells. Cells cultured in vitro can maintain some of the individualGenetic characteristics, such as the presence or absence of some enzymes.Genetic research on cultured cells in vitro belongs toSomatic cytogenetics。The concept of parenthood in genetics can also be extended toDeoxyribonucleic acid(i.e. DNA) replication and evenmRNATranscription of, these aremolecular geneticsResearch topic.
Biogenicnucleus，chromosome, in DNA.Chromosomes appear in pairs, so DNA and genes appear in pairs.Under normal circumstances, there are 23 pairs of chromosomes, 46DNA molecule。
2、 Scope of genetics research
The research scope of genetics includesgenetic materialThere are three aspects: the essence of genetic material, the transmission of genetic material and the realization of genetic information.The transmission of genetic material includes the replication of genetic material, the behavior of chromosomes, genetic laws and the quantitative changes of genes in the population.The purpose of modern genetics is to find out the internal mechanism of the whole genetic process.[1]
By aZygoteGeneratedImmunocompetent cellIt can produce different antibody globulins, which is also a subject of genetics. Its research belongs toImmunogenetics。[2]
fromphageTo people,BiosphereThere are basically consistent laws of heredity and variation, so genetics does not divide disciplines by biological objects in principle.The division of human genetics is because the study of human genetics is closely related to human happinessGenealogical analysisandtwin method And so on are almost limited to human genetic research.
Microbial GeneticsBecause the system of microorganisms and higher animals and plants is very different, special methods must be used for research.In addition, there are also someBiological nomenclatureBranch disciplines of, such aspoultryGenetics, cotton genetics, rice genetics, etc.
Disciplines for genetic research from the perspective of population includePopulation genetics、Ecological genetics、Quantitative genetics、Evolutionary geneticsEtc.These disciplines are closely related, and the boundaries are difficult to divide.Common Mathematics of Population Geneticsmethod studyDynamics of genes in population, studying gene mutation, natural selection, population size, mating system, migration andDriftAnd other factorsgene frequencyAnd gene balance;Ecological genetics studies biology and biology, as well as biology and environmentMutual adaptationOr the genetic basis of influence, oftenField workResearch in combination with laboratory workPolymorphism、MimicryAnd so on to verify the conclusions obtained in population genetics research;The research contents of evolutionary genetics includeOrigin of life、genetic material、Genetic codeAnd the evolution of genetic institutions andspeciationThe genetic basis.The study of speciation is also related toPopulation geneticsEcological genetics is closely related.
From the perspective of application, medical genetics is a branch of human genetics, which studiesHereditary diseaseThe genetic law and essence of;Clinical genetics researchHereditary diseaseDiagnosis and prevention of;EugenicsIt is the principle of genetics that is improving human beingsGenetic qualityApplication in.Genealogical geneticsOr quantitative geneticsQuantitative trait, while crops andlivestockMost of the economic traits of are quantitative traits, so they are the theoretical basis of animal and plant breeding.
Biochemical methods are widely used by almost any branch of genetics, and are more necessary for molecular genetics.In molecular geneticsRecombinant DNA technologyorgenetic engineeringTechnology has gradually become a powerful tool in genetic research.
Human beingsNeolithic AgeHas already domesticated animals andCultivated plantAnd then people gradually learned to improveAnimal and plant varietiesMethod.SpainIn his book "On Crops" written around AD 60, scholar Kolomela describedGrafting techniqueSeveral wheat varieties were also recorded.Chinese scholars from 533 to 544Jia SixieWritten in《Qi People's Essential Skills》The book discusses the cultivation of various crops, vegetables, fruit trees, bamboo trees andlivestockIn particular, it records the grafting of fruit trees,saplingReproduction,poultry, LivestockCastrationAnd other technologies.Improved variety's activities have never been interrupted since then.
Mendel
Many people try to clarify on the basis of these activitiesParental generationThe inheritance laws between the traits of the hybrid progeny and the traits of the hybrid progeny were not successful.Until 1866AustriascholarMendelAccording to the results of his pea hybridization experiment, he published the paper Plant Hybridization Experiment, which reveals thatMendel's lawOnly the genetic law of is able to lay the foundation of genetics.
Mendel's work was not valued until the beginning of the 20th century.In biology at the end of the 19th centurycell divisionThe research on chromosome behavior and fertilization process and the understanding of genetic material have promoted the development of genetics.
From 1875 to 1884, German anatomists andcytologyHome Fleming in Animals, GermanybotanistAnd cytologistStrasbergFound in plantsmitosis、MeiosisThe longitudinal division of chromosomes and the bipolar behavior after division;BelgiumZoologistBenedenIt was also observed thatParalumbricoides equiEach body cell contains an equal number of chromosomes;German zoologist Hertwig found fertilization in animals and Strasberg in plants;These findings areChromosome theory of heredityLaid the foundation.Wilson, an American zoologist and cytologist, summarized the discovery of this period in his book Cell in Development and Genetics published in 1896.
There has always been speculation about the material basis of heredity.For example, in 1864, English philosopher Spencer called it "living grain";1868 EnglandbiologistDarwinIt is called micro bud;1884SwitzerlandBotanist Negli called itHeterocytoplasm；In 1889, Dufresne, a Dutch scholar, called him a pan child;1883 German zoologistWeismann It is called germplasm. In fact, what Weisman said about germplasm is no longer a simple conjecture, and he has pointed out thatgerm cellThe chromosome of is germplasm, and it clearly distinguishes between germplasm and physique. It believes that germplasm can affect physique, but physique cannot affect germplasm, which opens the way for the development of genetics in theory
Mendel's work in 1900DeVriesGerman plant geneticistCollenceAnd the Austrian plant geneticist ChermarkPlant hybridizationIt was found by the scholars of the experimental work.From 1900 to 1910, it was confirmed that peas and corn in plants and chickens, miceguinea pigIn addition to conforming to Mendel's law, some basic concepts of genetics have also been established.1909DenmarkPlant physiologist and geneticist Johansson said thatGenetic factorIt is a gene with clear distinctiongenotypeAnd phenotype.Same yearBatesonAnd createdAllele、Heterozygote、HomozygoteAnd publishedRepresentativenessHis book is Mendel's Principles of Inheritance.[3]
Mendel's Three Laws
The development of genetics from 1910 to the present can be roughly divided into three periods: cytogenetics, microbial genetics and molecular genetics.
In this period, the chromosome theory of heredity was established by studying the laws of genetics and chromosome behavior.Morgan's Genetics in 1926 and Darlington's Latest Achievements in Cytology in 1932Two booksIt is a representative work of this period.In this period, although in 1927, American geneticist Miller and 1928, Stadler discoveredX-rayHowever, the research on the mechanism of gene mutation has not made progress.The important achievements of gene action mechanism research are almost limited to the genetic research of animal and plant pigments.
Microbial genetics
From 1940 to 1960, Bedell and Tatum published a report onneurospora From 1960 to 1961, French molecular geneticist Jacob andmono Published about E. coliOperonSo far.
genetics
During this period, microorganisms were used as materials to study the primary role of genesfine structure , chemical nature, mutation mechanism and bacterialGene recombination, gene regulation, etc., has made achievements that were difficult to obtain in the research of higher animals and plants in the past, thus enriching the geneticBasic theory。From 1900 to 1910, people only realized that Mendel's Law was widely applicable to higher animals and plants, while the achievements in the period of microbial genetics made people realize that the basic laws of genetics were applicable to people andphageAll creatures within.
Molecular genetics
In 1953, American molecular biologist Watson and British molecular biologist Crick proposedDouble helix of DNAThe model started, but only in the 1950sDNA moleculeSome achievements have been made in structure and replication, while genetic codemRNA、tRNA、ribosomeAlmost all of the functions of were initially clarified in the 1960s.
genetics
Molecular genetics isMicrobial GeneticsAnd biochemistry.Molecular geneticfundamental researchThe work is completed with microorganisms, especially Escherichia coli and its phages as research materials;Some of its important concepts, such as gene andproteinThe linear correspondence, gene regulation and so on also come from the research of microbial genetics.Molecular genetics inprokaryoteAfter many of the above achievements in the fieldEukaryoteIt has been carried out in all aspects.
Just as cytogenetic research has promotedPopulation geneticsLike the development of evolutionary genetics, molecular genetics has also promoted the development of other branches of genetics.genetic engineeringIt is found that bacterial plasmids, vaccine phages andRestriction endonucleaseDeveloped on the basis of research, it can not only be applied to industry, agriculture and medicine, but also further promote the research of molecular genetics and other branches of genetics.
immunologyIt is extremely important in medicine and has a long history.According to the hypothesis of one gene and one enzyme, why can an organism produce countless kinds ofimmunoglobulinThis is a molecular genetics problem in itself.sinceAustraliaIn 1959, immunologist Burnett proposedClonal selection theoryLater, the immune mechanism attracted the attention of many geneticists.At present, immunogenetics is not only one of the more active fields in genetics, but also one of the active fields in molecular genetics.
In the era of molecular genetics, the other two rapidly developing branches of genetics are human genetics and somatic cytogenetics.Since the means of microbial genetics research has been adopted, genetic research can be carried out through in vitro cultured somatic cells instead of germ cells, and human genetics research has been developing rapidly.No matter what the research object istissue cultureGenetic research conducted by such methods belongs to somatic cytogenetics.On the one hand, somatic cytogenetic methods are widely used in the research of human genetics, and on the other hand, molecular genetic methods are increasingly used, such as genetic engineering methods to establish humanGene libraryAnd isolate specific genes from them for research.[4]
basic content
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The research scope of genetics includesgenetic materialThe essence of genetic material, transmission andgenetic informationThree aspects of realization.The essence of genetic material includes itsChemical essenceThe genetic information it contains, its structure, organization and changes;The transmission of genetic material includes the replication of genetic material, the behavior of chromosomesGenetic lawAnd the quantitative changes of genes in the population;The realization of genetic information includes the original function of genes, gene interaction,Gene actionRegulation andOntogenyThe mechanism of action of genes in.
genetics
OneZygoteadoptmitosisAnd produce numerous products with the sameGenetic compositionOfDaughter cellHow they differentiate into different tissues is a genetic subject, and research on this aspect belongs toGenetic genetics。The immune cells produced by a fertilized egg can produce differentantibodyGlobulinThis is also a subject of genetics. Its research belongs toImmunogenetics。
hemoglobinBe able tomammalOxygen is transported in the blood.It shows the structural changes of hemoglobin between oxygen carrying and deoxygenated states.
singleamino acidMutations cause hemoglobin to form fibers.Genes are usually encoded by the production of proteins (complexBiomacromolecule）To show their functional impact.Protein is a linear chain composed of amino acids, while geneDNA sequence(viaRNAAs an intermediate carrier of information) is used to generate the amino acid sequence of a specific protein.The first step of this process is to generate a sequence complementary from the DNA sequence of genesRNAMolecules, that is, gene transcription.
RNA molecules generated by transcription（Messenger RNA）Is used to produce the corresponding amino acid sequenceConversion processIt is called translation.Three in each group of nucleic acid sequencenucleotideForm aCodon, can be translated as one of the 20 amino acids that appear in proteins, and this correspondence is calledGenetic code。The transmission of this information is singledirectionalThat is, information can only be accessed fromnucleotide sequenceTo amino acid sequence, but not from amino acid sequencenucleotideSequence, this phenomenon isFrancis Crick be calledmolecular biologyCentral rule。
The specific amino acid sequence determines the uniquethree-dimensional structure, andprotein structureIs closely related to their functions.Some proteins are simple structural molecules, such as those that form fiberscollagen protein。Proteins can be mixed with other proteins orSmall moleculecombination;For example, a protein as an enzyme performs catalysis by binding to a substrate moleculechemical reactionFunction of.Protein structure is dynamic;For example, hemoglobin can undergo minor structural changes in the process of capturing, transporting and releasing oxygen molecules in mammalian blood.
There are also some genes that are transcribed into RNA molecules but not translated into proteins. These RNA molecules are calledNon coding RNA。In some examples, theseNon coding RNA molecule(e.gRibosomal RNAandTransport RNA）Folds to form structures and participates in some key cellular functions.Other RNAs (such as microRNAs) can also communicate with other RNAsMolecular hybridizationAnd play a regulatory role.Single nucleotide changes in gene sequence（CodonChange) may cause the amino acid sequence of the encoded protein to change accordingly.Since the structure of a protein is determined by its amino acid sequence, the change of an amino acid may affect the interaction with other proteins and molecules of the protein by destabilizing the structure or changing the surface of the protein, resulting in dramatic changes in the properties of the protein.For example,Sickle cell anemiaIs a kind ofHuman genetic diseases, is composed ofβ-GlobulinSubunitIt is caused by a nucleotide mutation in the gene ofphysical property；In this disease, mutant hemoglobin combines with each other and accumulates to form fibers, thus distorting thered blood cellThe shape of.These twisted sickle cells cannot flow smoothly in the blood vessels, and are easy to accumulate and block the blood vessels or be degraded, thus causing anemia.
Congenital acquired
In human genetic diseasesPhenylketonuriaMedium,environmental factorIt also has a significant impact.The mutation leading to phenylketonuria destroys the degradation of the bodyPhenylalanineThe ability to cause toxicIntermediate productMolecules accumulate in the body, causing serious progressivenessIntellectual hypoplasiaandepilepsy。Patients with phenylketonuria mutations need to follow a strict diet to avoid ingesting foods containing phenylalanine, so as to maintain a normal and healthy life.Siamese kittenIt has temperature sensitive mutation, which causes the difference of coat color.Although genes contain all the information about the required functions of organisms, the environment still plays an important role in determining the final phenotype of organisms;This duality is called“Congenital and acquired”In other words, the phenotype of an organism depends onHeredity and environmentInteraction.An example of this interaction is temperature sensitive mutation: a single amino acid mutation in a protein sequence usually does not change the behavior of the protein and its interaction with other molecules, but can make the protein structure unstable.In aHigh temperature environmentThe movement of molecules is accelerated, and the collision between molecules is also strengthened, which makes the structure of this protein destroyed and unable to play its function;And in aLow temperature environmentHowever, the protein structure can remain stable and function normally.The changes caused by such mutations can be observed in the changes of hair color of Siamese cats.The cat's enzyme responsible for producing pigment contains a mutation, which can cause the enzyme to become unstable and lose its function at high temperature.So, in catsskin temperature The lower part (such as limbs, tail, face, etc.) is dark, while the higher part is light.
gene regulation
multicellular organismIngene expressionThe difference is very obvious: although all kinds of cells contain the samegenomeHowever, due to different gene expression, it has different structure and behavior.All cells in multicellular organisms originate from a single cell. They constantly differentiate in response to external or inter cell signals and gradually establish different gene expression rules to produce different behaviors.Because no single gene can be responsible for the development of various tissues in multicellular organisms, these laws should come from the complex interactions between many cells.All these processes must passgene regulation To complete.Transcription factors bind to DNA and affect the transcription of the associated genes.An organism's genome contains thousands of genes, but not all genes need to remain active.Gene expression is expressed as being transcribed intomRNAAnd then translated into protein;There are many ways to control gene expression in cells, so that the production of proteins can meet the needs of cells.One of the main regulatory factors controlling the "switch" of gene expression istranscription factor；They are a kind of geneticStarting siteThe regulatory protein on the can activate orSuppressor geneTranscription of.For example, inEscherichia coliThe bacterial genome contains a series of genes needed for tryptophan synthesis.However, when bacterial cells can be obtained from the environmentTryptophanThese genes are not needed by cells.The presence of tryptophan directly affects the activity of these genes, because tryptophan molecules will interact with tryptophanOperon(a transcription factor) binding, causing structural changes in the operon, so that the operon can bind to the gene required for tryptophan synthesis.Tryptophan operonIt blocks the transcription and expression of these genes, thus exerting negative feedback regulation on the process of tryptophan synthesis.
EukaryoteIntracorporealChromatinThere is energy influence inGene transcriptionThe structural characteristics of, often in the form of DNA and chromatin modification (such as DNA methylation), canStable hereditytoDaughter cell。These characteristics are "additive" because they exist at the "top" of the DNA sequence and can be obtained from aCytogeneticsTo its next generation.Because of these additional featuresculture mediumDifferent cell types growing in the cell still maintain their different characteristics.Although additive characteristics are usually dynamic throughout development, there are some, such asParamutationParamutation can be inherited for many generations, which is also a rare exception to the general rule that DNA is the molecular basis of heredity.
Relationship and application
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Biochemical relationship
Genetics andbiochemistryIt has the closest relationship with many other branches of biology.Such as genetic andDevelopmental biologyRelationship between;behavioral geneticsPeer is the relationship between biology;Ecological geneticsAnd ecology.In addition, genetics andtaxonomyThey are also closely related, not only because of the application of DNA in taxonomyBaseComponents and chromosomes are used as indicators, but also because the essence of species must be understood from the perspective of genetics.
Each branch of biology studies the structure and function of organisms at all levels. None of these structures and functions is not the result of the interaction between genetics and environment, so many disciplines are difficult to leave genetics in terms of concept and method.for examplehormoneMechanism of action andimmune reactionThe mechanism has always been regarded as a physiological problem not directly related to genetics, but now it is known that the former is related to gene activation, and the latter is different from the bodyImmunocompetent cellThe selection of clones is relevant.
genetics
1920s
Applied in the United States in the 1920sHeterosisThis genetic principle has achieved remarkable yield increase effect in maize breeding;This principle was successfully applied to rice production in China in the 1970s.polyploidThe growth advantage of has also been applied in China,TriticaleAllopolyploidThe successful cultivation of is an example.Artificial mutagenesisIt is also one of the widely used breeding methods.Quantitative geneticsandBiostatisticsThe research results of genetics have been applied to animal and plant seed selection to improve breeding efficiency.These are mainlycytogeneticsThe application of the research results of the period.
1940s
In the early 1940s,antibioticsThe rise of industry has promotedMicrobial GeneticsThe development of microbial genetics has promoted the antibiotic industry and other emergingFermentation industryProgress.With the deepening of microbial genetics research,gene regulation The principle of action was successfully applied toamino acidAnd other fermentation industries.In addition, the use of cross transduction, transformation and other technologies has also increased the means of breeding.
1970s
1970ssomatic cellThe development of genetics has further increased the means of breeding, including the so-calledHaploid breedingAnd through somatic mutagenesis andcell fusionBreeding, etc.The application of these means will probably greatly accelerate the process of breeding work.
Genetic research is closely related to human beings.With the development of human genetics research, especially the applicationSomatic cytogeneticsandBiochemical geneticsThe progress made in the methodgeneticThe types and causes of diseases have been well understood;prenatal diagnosis And the heredity of babiesdisease diagnosis It has been gradually popularized;For some hereditary diseasesmedicationAlso under study.Immunogenetics isTissue transplantationAnd blood transfusion;Pharmacogenetics is closely related to pharmacology;Toxicological geneticsIt is related to the safe use of drugs and environmental protection.Use heredityEngineering technologyFor hereditary diseasesgene therapyIt is also being explored.Human genetics research is alsoEugenicsThe foundation of.
Genetic research isCarcinogenThe detection of provides a series of methods.Although there is no effective method to treat cancer at present, it is a significant progress to effectively detect carcinogens in the environment today when environmental pollution is becoming increasingly serious.CancerousTendentiousnessIt's hereditary, and the cause of cancer is the sameDNA damage repairIn recent years, the discovery of oncogenes further demonstrates the close relationship between cancer and heredity, so in the long run, genetic research will contribute to the overall control of cancer.
Many branches of genetics have adoptedmolecular geneticsMeans, especially restructuringDHATechnology.Even the genetic research of relevant populations is affected by molecular genetics,Evolutionary geneticsUnder studymolecular evolutionThe domain is an example.
In recent years,human genomeThe research progress is changing with each passing day, andMolecular Biology TechnologyIt is also constantly improved, withgenomeWith the continuous penetration of research into various disciplines, the progress of these disciplines has reached an unprecedented height.stayforensic medicineUpper, STR site andMononucleotide（SNP）Site detection is the core of the second generation and the third generation of DNA analysis technology, and it is the successor to RFLPs（Restrictive fragment length polymorphism）VNTRs (variable quantityTandem repetitionSequence polymorphism)Detection technology。As the most advanced criminal biotechnology, DNA analysis provides a scientific, reliable and fast means for forensic material evidence testingIdentification of physical evidenceFrom individual exclusion to being able to doestablishing identityDNA test can directly identify crimes, murder cases, rape homicide cases, dismemberment cases, rape induced pregnancy cases and other major casesDifficult caseThe detection of the crime provides an accurate and reliable basis.With the development and application of DNA technology, the detection of DNA marker system will become an important means and approach to solve cases.This method is used asPaternity testIt is already very mature and internationally recognized as the best method.
New trends
1991-1997, ChinaZeng Bangzhe[Jie] (Zeng BJ.) published a series of papers on Structure Theory - Pan Evolution Theory, explaining the systemMedicine（systems medicine）、Systems Bioengineering(system biological engineering) andSystematic genetics(system genetics)Development concept, and at the International Genetics Conference in 2003 and 2008, we used the vocabulary of structure, system, and pattern genetics to describe system science methods, computertechnical study Biological systemThe complexity of "genotype expression" between genetic structure and morphological schema of biological systemsystem study The field focuses on cell signal transduction and gene regulation network to study cell nonlinearity in cell evolution, cell development, cell pathology, and cell pharmacologysystem dynamics 。
2003NorwayScientists called it integrated genetics and established a research center. In 2005, Cambien F. and Laurence TArteriosclerosisIn 2007 (Bock G., Good J. Eds.), Morahan G., Williams RW. et al. discussed that system genetics will become the next generation of genetics.From 2005 to 2008, international systematic genetics developed rapidly,Europe and AmericaMany systems genetics research centers and laboratories have been established.In 2008, the International Conference on Integration and Systemic Genetics was held in the United States. In 2009NetherlandsInternational Conference on Systemic Genetics, 2008National Institutes of Health(NIH) set uptumourSystemic genetics research ofSpecial fund。Systemic genetics, usingComputer modeling, system mathematical equation, nano high flux biotechnologyMicrofluidic chip Experiment and other methods to study the structural logic and genomefine structure EvolutiongenomeStabilityBiomorphologyCytogenetic nonlinearity of schematogenesissystem dynamics 。
At the beginning, geneticists studied a wide range of subjects, but gradually concentrated on the genetics of some specific species (model organisms).This is because new researchers tend to choose some organisms that have been widely studied as research objectives, making model organisms the basis of most genetic research.The genetic research of model organisms includes gene regulation, development and cancer related genes.
The purpose of medical genetics is to understandGene variationRelationship with human health and disease.When searching for an unknown gene that may be related to a certain disease, researchers usually usegenetic linkageAnd genealogy to locate the regions of the genome associated with the disease.At the population level, researchers will use Mendelian random method to find regions related to the disease in the genome, which is also particularly applicable to those that cannot be defined by a single genePolygenic trait。oncecandidate gene If found, it is necessary toModel organismCorresponding genes in（Orthologous homologyGenes).For the study of genetic diseases, more and more developed techniques for studying genotype have also been introducedPharmacogeneticsTo study how genotype affectsDrug reaction。
cancerAlthough not in the traditional senseHereditary disease, but is considered aHereditary disease。The generation of cancer in the body is a comprehensive event.There is a certain probability that cells in the body will mutate in the process of division.Although these mutations will not be passed on to the next generation, they will affect the behavior of cells and in some cases lead to more frequent cell division.There are many biological mechanisms that can prevent this from happening: signals are transmitted to these abnormal dividing cells and cause their death;But sometimes more mutations cause cells to ignore these signals.At this time, natural selection and gradual accumulation of mutations in the body make these cells begin to grow without restriction, thus becoming canceroustumour(malignant tumor) and infect various organs of the body.[6]
DNA can be manipulated in the laboratory.Restriction endonucleaseIt is a common cuttingSpecificityA sequence of enzymes used to produce predetermined DNA fragments.Then useDNA ligaseReconnect these fragments and connect DNA fragments from different sources together to obtainRecombinant DNA。Recombinant DNA technologyIt is usually used in plasmids (short circular DNA fragments containing a small number of genes), which are often associated withTransgenic organismIs related to manufacturing.Transfer the plasmid into bacteria, and thenPlate culture mediumThen researchers can use the cloned colonies to amplify the inserted plasmid DNA fragments (this process is called molecular cloning).
DNA can also pass through aPolymerase chain reaction(also known asPCR）To amplify.Use specific shortDNA sequence，PCR technologyIt can isolate and amplify target regions on DNA.Because only a small amount of DNA can be amplified, this technology is often used for DNA detection (to detect the existence of specific DNA sequences).
Sequencing and Genome
DNA sequencingTechnology is the most basic technology developed in genetic research, which enables researchers to determine thenucleotide sequence。fromFrederick Sanger And his colleagues in 1977Chain terminationSequencing is nowDNA sequencingConventional means.With the help of this technology, researchers can study DNA sequences related to human diseases.
Because sequencing has become relatively cheap, andcomputer technologyWith the help of, a large number of different pieces of sequence information can be connected (this process is called "genome assembly"), so many biological (including human)Genome sequencingAlready completed.These techniques are also used to determine humangenome sequence, makinghuman genome projectIt was completed in 2003.With the newHigh throughput sequencingWith the development of technology, the cost of DNA sequencing has been greatly reduced. Many researchers hope to reduce the price of determining a person's genome information to less than 1000 dollars, thus making it possible for public sequencing.
A large amount of genome sequence information has given birth to a new research field——GenomicsResearchers use computer software to find and study the laws existing in the whole genome of organisms.Genomics can also be classified as a field under bioinformatics, which uses computational methods to analyze biological data.
Gene abnormality
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One or more gene abnormalities, especiallyRecessive gene, is quite common.Everyone carries 6~8 abnormal recessive genes.However, these genes do not cause cell dysfunction unless there are two similar recessive genes.In the general population, the probability of individuals with two similar recessive genes is very small, but in theInbreedingOf the children, the probability is higher.In the group of inbreeding, such as Oman in ChristianityMennonites , the probability is also high.
A person's genetic composition is calledgenotype。The reflection of these genes in the human body, that is, the expression of genotype, is calledphenotype。
All genetic characteristics (traits) are encoded by genes.Some characteristics, such as hair color and differences between people, cannot be regarded as abnormalities. Howevergene expressionThe generated abnormal characteristics may causeGenetic disease。
Single gene abnormality
The effect of a single gene abnormality depends on whether the gene isdominanceOr recessive gene, and whether this gene is located on the X chromosome（X interlock)。Because a gene directs the synthesis of a specific protein, abnormal genes may occurAbnormal proteinQuality or cause someprotein content Abnormality, and then lead to abnormal cell function, and finally lead to abnormal body shape or function.
Chromosome heredity
be locatedAutosomeException onDominant geneThe resulting trait can lead to malformation, disease or a tendency to develop into a disease.
The following principles generally apply to traits determined by dominant genes:
A person with this trait has at least one parent with the same trait, unless the trait is caused by a new gene mutation.
abnormalGenetic traitIt is often caused by new genetic mutations rather than by parents.
When one parent has an abnormal trait and the other does not, each of their children has a 50% chance of inheriting the anomaly and a 50% chance of not inheriting the trait.If one of the parents has two such abnormal genes (although rare), all their children will have abnormal traits.
An individual without abnormal traits, even if his brother or sister has abnormal traits, because he does not carry this gene, his children will not inherit abnormal traits.
Men and women are equally likely to be affected.
Exceptions often occur in every generation.
The following principles generally apply to traits determined by recessive genes:
In fact, both parents of a person with this trait may carry this recessive gene, but neither parent shows this trait.
Mutations rarely cause the expression of this trait.
One parent shows a trait, the other carries a recessive gene, and has no trait. About half of their children may show abnormal traits;The other half will be recessivecarrier。If the other party does not carry abnormal genes, none of their children will show abnormal traits, but all their children will be carriers, and this abnormal gene can be passed on to their offspring.
A person without abnormal traits, if his brother or sister has abnormal traits, he is likely to carry one of these abnormal genes.
Men and women are equally likely to be affected.
It is usually not abnormal in every generation, unless both parents are abnormal.
Dominant genes that cause serious diseases are rare.Because these genes tend to disappear, people with dominant genes that cause serious diseases are often too sick to have fertility.However, there are a few exceptions, such asHuntington's chorea(See section 67), which can cause severe brain function decline. The symptoms often start after the age of 35. Before the symptoms, the patient may have a child.
The recessive gene can only be expressed when the individual has two identical recessive genes.An individual with only one recessive gene does not show traits, but he is the carrier of this recessive gene and can pass this gene on to his children.
X-linked gene
Because maleY chromosomeThe number of genes on a single X chromosome (X-linked genes) is very small.Therefore, both dominant and recessive genes can be expressed.However, women have two X chromosomes. Those principles that apply to genes on autosomes also apply to women's X-linked genes.Unless the two paired genes are recessive, only dominant genes can be expressed.
If an abnormal X-linked gene is dominant, the affected man will inherit the abnormal gene to all his daughters, but not to his son.The son of the affected man receives his Y chromosome, which does not carry abnormal genes.A woman with only one abnormal gene can pass on the abnormal gene to half of her children, sons or daughters.
If the abnormal X-linked gene is a recessive gene, almost all of the abnormal characters are male.Abnormal men only transmit abnormal genes to their daughters, who are carriers.The mother of the carrier does not show abnormalities, but can pass on the abnormal genes to half of her sons, who often show abnormal traits.Their daughters have no abnormal traits, but half of them are carriers.
Red green colour blindness, caused by X-linked recessive gene, maleincidence rateAbout 10%, while womenNot common。In men, causeColor blindnessThe gene of is from the mother, who is a color blind patient or a color blind gene carrier with normal vision.The color blindness gene does not come from the father because the father provides the Y chromosome.The daughter of a color blind father is rarely color blind, but is often the carrier of color blind genes.
Every cell hasmitochondrionThis is a tiny structure that provides cell energy.Each mitochondrion contains a ring chromosome.Several rare diseases are caused by abnormal genes carried by chromosomes in mitochondria.
WhenEgg cellDuring fertilization, only the mitochondria of the egg cell become part of the developing fetus;All mitochondria of sperm were discarded.Therefore, abnormalMitochondrial geneThe resulting disease is inherited through the mother.A father with abnormal mitochondrial genes will not inherit such diseases to his children.
