Cytogenetics is also a branch of genetics that studies genetics at the cellular level.
Cytogenetics is established by combining genetics and cytology, mainly from the perspective of cytology, especially fromchromosomeAnd the relationship between chromosome and other organelles.
Cytogenetics is the combination of genetics andcytologyA branch of genetics that combines.The main research objects areEukaryote, especially including humanHigher animals and plants。
Early cytogenetics focused on researchseparate、recombination, chain, exchange, etcGenetic phenomenonOfchromosomeBasic and chromosomal aberrations andPloidy changeThe genetic effect of isochromosomal behavior, and involves various reproductive modes such asApomixis、Parthenogenesisas well asMeiotic driveAnd other aspects of genetics and cytology.Later, some branch disciplines were derived, and the research content was further expanded.
At the end of the 19th century,Mendel's lawShortly after being rediscovered, Sutton, an American cytologist, conducted experiments with GermanyembryologyGabovilli'sMeiosisDuring the process, we found that chromosome behavior andGenetic factorThe parallel relationship between behaviors is that Mendel's genetic factors are on chromosomes, which is the so-called Sutton Boweri hypothesis orChromosome theory of heredity。
From 1901 to 1911, American cytologists McLang, Stevens and Wilson successively found that there was one more female than male in Orthoptera and HemipterachromosomeX chromosome, which reveals the relationship between sex and chromosome.
1902-1910 British geneticistBatesonHe extended Mendel's law to animals such as chickens and rabbits and plants such as sweet peas, and created a series of genetic terms: genetics, homoplasm, heteroplasmAllele, mutual attraction and mutual exclusion, etcMendelian geneticsThe foundation of.
From 1910 to the mid-1920s, American geneticists Morgan, Bridges and Stevient used fruit flies as research materialsInterlocking and switchingThe concept of mutual attraction and exclusion has been replaced by the concept ofThree point quizBasedGene mappingMethods, it was confirmed that the genes work in a linear arrangement on the chromosome, so thatChromosome theory of heredityIs established.Cytogenetics has developed rapidly on this basis.
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Branches derived from cytogenetics mainly includeSomatic cytogenetics——It mainly studies the genetic law of somatic cells, especially the cells of higher organisms cultured in vitro;Molecular cytogenetics - main researchchromosomeOfSubmicrostructureAnd gene activity;Evolutionary cytogenetics - mainly studies chromosome structure and ploidy changes andspeciationRelationship between;Organelle genetics——Mainly study organelles such aschloroplast, mitochondria, etcgenetic structure ；Medical cytogenetics, which is a new development combining the basic theory of cytogenetics with clinical medicineMarginal science, Researchchromosome aberrationThe relationship with genetic diseases is of great significance for genetic counseling and prenatal diagnosis.
Mendel's lawIt reveals thatSexual reproductionBased on the laws of genetics.But there are also different reproductive modes in the biological world, such asApomixis、Parthenogenesis、Parthenogenesis。In the offspring obtained through these reproductive methods, the proportion of traits does not conform to Mendelian proportion.In addition, phenomena that do not conform to Mendel's law may also occur in the process of general sexual reproduction, such asMeiotic driveThe study of these phenomena also belongs to the category of cytogenetics.
Cytogenetics is the earliest and most basic discipline in genetics.Other branches of genetics are developed from it, and the basic laws expounded in cytogenetics are applicable to all branches, including molecular genetics.
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chromosomeCarrying genetic material.Understanding the structure and function of chromosomes is one of the important tasks of genetics.The abnormality of chromosome number and structure is associated with many diseases, including hereditary diseases related to gynecology and obstetrics.Therefore, chromosome analysis under microscope is a useful tool for examination and diagnosis of genetic diseases in gynecology and obstetrics.
1. Guidelines for cytogenetic analysis:
① Confirm and exclude the diagnosis of some known chromosome syndromes;
② Sexual differentiation and abnormal development;
③ Infertility;
④ Repeated abortion or stillbirth;
⑤ Pregnancy with aneuploidy risk revealed by maternal serum screening or fetal ultrasound;
chromosomeIt is prepared from dividing cells.These cells can be taken directly from fresh tissue, such asVillous tissue；It can also be taken fromcell culture, such as amniotic fluid cell culture.The most widely used specimen for karyotype analysis is peripheral blood, which is prepared from bloodT lymphocytesChromosome analysis.
The air dried chromosome drops must be suitable for staining before they can be put under the microscope for karyotype analysis.
① Chromosome dyeing uses Giemsa and other dyes with affinity to DNA to darken chromosomes.This staining method can be used to check the fragile parts of chromosomes, chromosome breakage syndrome and chromosome damage caused by radiation. ②G banding is a routine method for analyzing human chromosome diseases. ③One disadvantage of R banding and G banding is that the telomere region is light stained. With R banding, we can get the type of staining band just opposite to G banding. ④Q banding and DNPI banding Q banding was stained with quinacrine nitrogen mustard,chromosomeThe fluorescent band type with different light and shade is displayed under the ultraviolet lamp, and the band type is the same as that of G band.Q-banding can be used to identify the satellite region of the telocentric chromosome. ⑤C banding and anti staining banding are not commonly used. ⑥Nucleolar organizer region(NOR) silver staining, etc.
4. Flow karyotype analysis:
For cell suspension samplesFlow cytometryFlow karyotype analysis.Flow cytometry can measure the DNA content of individual chromosomes.Chromosome suspension is fluorescent stained, and then the fluorescence intensity of each chromosome excited by laser is measured with a photon amplifier.This test can be used for sex identification, aneuploidy detection andchromosomeDetermination of size anomalies.
The probes for in situ hybridization can be labeled with nuclide or fluorescein.in recent yearsFluorescence in situ hybridizationThe use of has become common.If multi-color fluorescent labeling is used, multiple probes can be used at a time to check multiple specific DNA sequences.For example, combine the multi-color fluorescence in situ hybridizationfluorescence microscopeWith the help of imaging processing system, the resolution and accuracy of chromosome analysis can be enhanced.[1]
