“Genetics is a field of Science that studies DNA, genes, chromosomes, genome, genetic variations, mutations and inheritance of traits. Depending upon its applications, genetics is divided into various branches, here are some.”
Genetics is an interdisciplinary field of biology that mainly deals with DNA studies. Gregor John Mendel was the pioneer in the field of genetics, who conceptualized and eventually popularized it during the late 18th century.
Mendel J postulated two critical genetic phenomena which scientists still use to study various mutations and genetic disorders. Timely, the field evolved and discoveries, findings and ideas came into the picture.
Now the field of Genetics is a mainstream science subject and covers many topics from microbial genetics to plant genetics. It is divided into different fields to cover various studies comprehensively. Eventually, it makes students understand each topic/field and choose their own.
In this article, I have explained important branches of genetics and some of the crucial applications of genetic science. This article helps students understand genetics and its branches more thoroughly and choose their own.
|DNA||DNA is a polynucleotide chain made up of sugar, phosphate and nitrogenous bases.|
|Gene||A functional part of DNA is a gene.|
|Chromosome||A complex network of proteins and DNA where all the genes are located is known as a chromosome.|
|Genome||A complete haploid set of DNA of an organism is a Genome.|
|Genotype||A heritable unit of DNA that produces a specific phenotype is a genotype.|
|Phenotype||A visible or observable trait, governed by genotypes is known as a phenotype.|
|Mutation||Any structural change in DNA is known as a mutation.|
|Genetic engineering||A field of genetics in which genetic manipulation is conducted for various purposes is known as genetic engineering.|
|Allele||An alternative form of a gene is an allele.|
|Trisomy||The presence of three similar types of chromosomes instead of a pair.|
|PCR||PCR is a technique to study DNA.|
|Gene mapping||Finding gene location in a genome or on a chromosome is known as gene mapping.|
Branches of Genetics
As the name suggests, classic genetics is the oldest form of genetic science that highly relies on the principle of Mendel- the law of inheritance and independent assortments. It mainly uses the Mendelian inheritance phenomena.
The law states that genes are inherited from each parent to their offspring. The fundamentals of classical genetics were used to study and experiment on various plant species. Put simply, Mendel’s laws are the basic foundation of classic genetics.
Cytogenetics is the most traditional, well-established and well-studied branch of genetics. This interdisciplinary field majorly studies chromosomes using various techniques. The major objectives of cytogenetics are to study the structure and numbers of chromosomes and thereby find abnormalities.
It has crucial significance as it is used in medical science to study and identify chromosomal disorders. The study of chromosomes allows us to identify disorders like down syndrome, Patau syndrome, Klinefelter syndrome and other abnormalities associated with chromosomes.
|Down Syndrome||Numerical||Trisomy 21|
|Klinefelter Syndrome||Numerical||XXY in males|
|Turner Syndrome||Numerical||XO in female|
|Philadelphia Syndrome||Structural||Translocation between chromosomes 9 and 22|
|Neuroblastoma||Structural||Chromosome 1p deletion|
|3q del||Structural||Deletion of the q arm of chromosome 3|
Techniques like conventional karyotyping in which chromosomes are studied from the metaphase cultured cells is the basic, popular and well-accepted scheme here. However, recently involved molecular cytogenetics techniques– FISH and Microarray are now available options for testing.
Both techniques can investigate alterations that commonly can’t be studied by conventional karyotyping. To learn more about cytogenetics, techniques, history and cancer cytogenetics, please read our previous article.
Related article: A Brief Introduction To Cytogenetics.
Cytogenetics can study chromosomes but what if we want to study DNA? it can’t work. Molecular genetics studies genetics at the molecular level– DNA, nucleotide sequences and sequence alterations.
Molecular genetics became popular after the discovery of the molecular and chemical structure of DNA by Watson and Crick in 1953. Elaboratively, it studies the molecular structure of DNA or gene viz, nucleotides, nitrogenous bases, sequence alterations and sequence abnormalities, etc.
Notedly, change even at a single nucleotide (SNP) can be investigated using molecular genetic techniques. Here is a list of some disorders with problems at the DNA level.
|Sickle cell anemia||Beta globin gene||Single gene disorder|
|Thalassemia||Beta globin gene||Single gene disorder|
|Cystic fibrosis||CFTR gene||Single gene disorder|
|Hemophilia||F8 and F9||Polygenetic|
|Duchenne muscular dystrophy||DMD||Single gene disorder|
To study sequences at a molecular level, techniques such as Polymerase Chain Reaction, DNA sequencing, Restriction digestion and traditional and advanced hybridization-based assays are used.
Each technique has its own importance, advantages and limitations. If you wish to learn each technique more comprehensively you can refer to this table.
|Technique||Application||Link for the article|
|PCR||To study gene or DNA mutations.||Polymerase Chain Reaction|
|DNA sequencing||To study a gene or DNA at the sequence level||DNA sequencing|
|Restriction digestion||To study a gene or alleles associated||Restriction Digestion|
|RT-PCR||Quantitative analysis of DNA||Real-Time PCR|
|DNA markers||To study various regions in the genome||Genetic markers|
Further to this, the present field also deals with gene expression studies which we will cover separately in the upcoming section. Note that molecular genetics studies the DNA of any organism.
So if we want to study the DNA or genes of plants, bacteria, fungi or even viruses, we use molecular genetic techniques or analysis tools.
Microbial genetics is an interdisciplinary field of genetics, focusing on the study of the genetics of microorganisms– like bacteria, viruses, fungi, protozoa and archaea. Alternatively saying— the field is the most advanced version of microbiology.
Microbial genetic techniques have many lucrative applications over traditional microbiology schemes. Firstly, it’s safe, fast, reproducible and accurate. Secondly, it allows us to study evolution too.
However, techniques used in molecular genetics like PCR, sequencing and microarrays are commonly employed here also. In medical science, it is used to study infectious pathogens, and monitor and prevent their spread, thereby helping to study antibiotic resistance and relevant phenomena.
It has therapeutic applications as well, as it is used in the production of recombinant components and recombinant DNA and vaccines.
In trends, genetics and genetic tools are popularly employed for human genetic studies. It deals with the study of human DNA, genes, chromosomes, associated disorders and how alteration within the human genome occurs.
Inherited human disorders like thalassemia, sickle cell anemia, Huntington’s disease, etc are now screened using genetic techniques. It studies the inheritance pattern, severity of the disease and probability of passing down.
State-of-art techniques are now capable enough to study various types of cancer and are used as a tool for cancer management, prevention and prognosis studies. Common study areas in this field are—
- Autosomal disorders (dominant and recessive)
- Sex-linked disorders (dominant and recessive)
- Pedigree analysis
- Population studies
- Evolution studies
- Disease origin and prognosis
Interestingly, the human genome project was the largest genetic project so far conducted, and completed in 2003. The field of human genetics not only studies genetic disease (which is separately discussed in the clinical genetic part) but also DNA sequences, non-coding and coding sequences of the genome.
Some outputs of the human genome project are listed here.
|Human genome||3.2 billion base pairs|
|No. of genes||23,000|
|Coding: non-coding ratio||3:97%|
|No of chromosomes||46 (23 pairs)|
|Common genetic disorders||Thalassemia, sickle cell anemia, Down syndrome, breast cancer and Inherited cancer.|
In layman’s terms, clinical genetics deals with the patient’s care; henceforth, we can say it’s similar to human and medical genetics, but technically— a bit different. Clinical genetics has applications in the diagnostic industry, majorly.
Clinicians perform various tests to identify gene mutations, genomic alterations, cancer-causing locus, chromosomal alterations, inheritance patterns, genetic disease and other related problems that cause serious health complications.
Clinical genetics identifies–
- Chromosomal abnormalities
- Birth defects
- Inherited conditions
- Genetic problems
- Cancer-causing genes
- Family risk of carrying disease
- Mental, physical or developmental abnormalities
Genetic counseling is also a part of clinical genetics in which clinicians aware patients of genetic conditions. Here are glims of clinical genetics in a table.
|Chromosomal defects||Down syndrome, Patau syndrome, Klinefelter syndrome and Turner syndrome|
|Gene mutations||Thalassemia, sickle cell anemia, cystic fibrosis, Huntington’s disease, muscular dystrophy and neurofibromatosis.|
|DNA alterations and cancer||P53, BRCA, EGFR, MTHFR and MYC gene mutations|
|Congenital conditions||Birth defects, neural tube defects, cleft pellets and cognitive defects.|
|Reproductive defects||male/female infertility, reproductive failure, sex reversals, recurrent miscarriages, etc.|
|Mental and cognitive defects||Autism spectrum disorders, down syndrome, learning difficulties, etc.|
|Neural and motor defects||Spinal muscular atrophy, myotonic dystrophy, Duchenne muscular dystrophy, Rett syndrome and Huntington’s disease, etc.|
|Metabolic disorders||Tay-Sach disease, Wilson disease, Maple syrup urine disease, biotinidase deficiency, etc.|
|Blood disorders||Thalassemia, sickle cell anemia, hemophilia and leukemia|
|Cancer||Inherited cancer, leukemia, ovarian cancer, prostate cancer, glioblastoma, colon, and bladder cancer, etc.|
The field of medical genetics is not different than clinical genetics. Notwithstanding, clinical genetics majorly focused on disease and disease diagnosis, and medical genetics additionally finds the cause and work for the management of any disease.
Furthermore, it also covers the study of infectious pathogens, their spread and their role in disease development. For example, Malaria and TB pathogens are now studied using techniques like RT-PCR.
Quantitative analysis of pathogens and infections and sequence variations are also studied by techniques like quantitative PCR and DNA sequencing, respectively. The detailed scenario for each point is covered in the clinical and microbial genetics sections.
How can we say if a new sequence or gene variation or mutation is pathogenic or not? By knowing its effects on the larger group of people. That’s exactly what we study in population genetics.
Put simply, population genetics studies the gene pool or biological composition of the entire single population, their effect on other populations, individuals and related consequences. Mathematical and statistical calculations are the foundations to collect informative and quantitative data.
For example, gene frequency, allele frequency or distribution of mutation are several parameters population geneticists investigate frequently. So it studies genetic differences within and between the population and their consequences at an individual level.
Evolutionary factors (that we will discuss separately in another section) like selection, genetic drift, gene flow and mechanism of evolution can also be studied. However, it’s also important to note that it includes wet lab experimentations too.
The scheme is as follows– sample collection, testing or experimentation, statistical analysis (gene/genotype/allele frequency) and population analysis.
The study of gene expression and not gene alteration is covered in epigenetics. It’s an interdisciplinary field of genetics and studies gene expressions in different tissues and organisms.
Altered gene expression commonly causes cancer and is the main focus of epigenetic studies. Altered gene expression simply means– up and down-regulation of gene expression from its normal state. Gene expression simply means how many copies of a particular gene are formed in a cell.
Methylation, histone modifications, acetylation, and ubiquitination are common mechanisms involved in the on and off of gene expression. For example— the addition of methyl groups makes the gene transcriptionally inactive.
When the entire mechanism is disrupted by either extrinsic or intrinsic factors, it causes epigenetic dysregulation and eventually, cancer. RT-PCR, transcriptomics analysis, microarray and methylation sequencing are some of the few techniques used in epigenetic studies.
These techniques study gene expression from various cells, tissues or organisms and find any abnormality in the pattern if occurred. To learn more about epigenetics, read this article: What is epigenetics?
One of the most emerging fields of genetics is metagenomics. The interdisciplinary field studies the entire pool of microbes or microbial diversity present in any specific sample which was previously not possible using traditional microbiology techniques.
So metagenomic analysis is fast, accurate, sensitive and reproducible. We can even find thousands to millions of microbes from a single sample; that level of power metagenomics has.
A specialized sequencing setup simultaneously finds every unique microbial sequence present in the sample. It can even quantify the amount of each microbe present in the sample. With this, the technique can even find any novel pathogen/microbe or new strain with utmost precision.
For example, through gut microbiome metagenomic studies, the entire population of useful and harmful microbes present in the gut can be investigated. Other common sample types for metagenomic analysis are gut, intestine, urine and feces samples and any environmental samples like— sea water, river water, decayed plants or mud, etc.
Applications of metagenomics are–
- Study of the microbial population from a sample
- Study of microbial biodiversity from various ecosystems
- Identification of novel microbes
- Role of microbes in human health
- Microbial evolution and biodiversity
Metagenomics is an interesting field but at the same time, is complex. It includes extensive wet lab work— sample preparation, testing, library preparation and sequencing, and complex dry lab work— bioinformatics analysis, sequence analysis, counting, pairing and aligning.
Read this article to learn more: What is metagenomics?
Genetic technologies are widely applied in plant research. In fact, major historical studies in genetics were conducted on plants. The same methods and techniques of molecular and cytogenetics are used in plant genetic research but give totally different and lucrative outcomes.
Scientists prepare various useful GMOs (Genetically modified organisms/plants) for various purposes. Some common purposes are
- Preparing economically important plants
- Improving the existing important traits.
- Improving the nutritional value of plants.
- Prevent plant species from pathogens and abiotic and biotic stresses.
- Plant evolutionary studies.
In modern trends, environmentalists use genetics for various ecological, environmental and diversity studies. They collect samples from ecosystems and closely investigate the composition of each system.
Environmental genetics brings into focus microbial diversity from various ecosystems and their benefits for the same. The general scheme here is to collect various biological samples from the environment and do genetic analysis.
Such environmental studies make us understand the composition of the environment, the role of different organisms in the ecosystem, causes of pollution, and biological pollutants and thereby environment strength and health.
They also study animal and microbial migration, observe their patterns and draw useful conclusions. Environmental studies using genetic tools revolutionalized the entire field as now such studies become more rapid, accurate and sensitive.
Take a look at some of the applications.
- Types of organisms present in the ecosystem.
- Microbial load, diversity and composition.
- Genetic composition and important genes of any ecosystem.
- Common environmental contaminants.
- Common environmental pollutants.
- Evolution and macroevolution in a particular environment.
- Biodegradation studies
- Biodiversity studies.
Genetic alteration is one of the evolutionary forces which is separately studied in evolutionary genetics. Genetic changes at the DNA, gene or chromosome level leads to changes in the genomic composition of organisms, timely.
Such changes produce new traits which are helpful for organisms to survive. Evolutionary geneticists study those forces and how they occurred over a course of time. It also allows them to draw an evolutionary relationship between organisms.
Scientists here study–
- Importance of genetic diversity in evolution.
- How diversity occurred.
- Why genetic evolution occurred.
- What genes evolved?
- Importance of gene pool and genetic drift.
- Creating relations between closely and distantly related organisms.
- Estimating the time of divergence between organisms.
Evolutionary genetics is a vast field. We will deeply look into the topic in some other article.
Google’s trend of the past several years shows significant growth and interest of people in the topic, “genetic engineering”, however, it’s not new. The definition suggests that by using genetic tools and techniques, any organism’s genome can be modified.
For the sole beneficial purpose, obviously.
The field is yet constantly growing at a rapid pace, new techniques are still added and becoming better day by day. Some common practices it involves are gene editing, genetic manipulation and gene therapy, etc.
Other than that, a common technology to look forward to is CRISPR-CAS9-based gene editing. There are many lucrative applications of genetic engineering and scientists are looking forward to using it to cure genetic diseases in near future.
The general scheme states that an organism’s target gene is replaced, edited or removed to nullify the harmful effect of the target gene. The normal function of such traits, if important, can be re-normalized by adding a new healthy gene.
We have covered a separate and comprehensive article on this topic including the general history, applications and of course, the process and steps involved. Give it a try: What is Genetic Engineering?- Definition, steps, process and applications.
Bioinformatics is a subdiscipline of science that runs by computational power and helps in biological processes, testing, results, evaluations and interpretation. Researchers can get access to other biological data and store their own.
Bioinformatic tools let scientists perform analysis using computational power. People often talk about BLAST, FAST, in silico PCR, NCBI and all those things while discussing bioinformatics, but the entire genetic analysis system is based on informatics.
For example, a PCR, a sequence or a microarray all that stuff runs on software and computational power. In addition, the backend of sample processing, testing and analysis is performed using a state-of-art instrument that also runs on the computer programs.
All these are part of actual bioinformatics. However, common and important tools for geneticists are listed here:
|Primer 3||Design Primers|
|BLAST (Basic Local Alignment Search Tool)||Aligns sequences and finds sequence similarities and differences.|
|In silico PCR||Performs PCR and amplification on computer software.|
|Genome data viewer||RefSeq genome assembly of more than 1740 organisms.|
|Genotyping tool||Help identify the genome of an organism|
Again like metagenomics or genetic engineering, bioinformatics is a huge field. We will cover an entire series somewhere on this blog.
These are some of the important fields of genetics. Now we will look at some other subsidiary branches of genetics.
The most emerging, fascinating and futuristic genetic branch is transcriptomics. The present discipline studies the transcriptome— the coding region or mRNA of the genome which is the expression profile of the entire genome of an organism.
In this field, scientists extract the mRNA which is transcribed from the coding DNA sequencing and investigate expression in various samples or tissues. In general, it gives us an idea regarding what genes are active and in how much quantity.
Techniques like RNA sequencing and expression microarrays are great tools for transcriptomics studies. And studies thousands of mRNAs in a single run.
Transcriptomics is applied in tissue-specific gene expression studies, cancer expression profiles, characterization of non-coding RNAs and disease research. If you would like to strengthen your knowledge on this topic, check out this article: What is transcriptomics?
As the name suggests, the genetic test is performed at the stage of pre-implantation– at an early embryonic stage. This technique is the most sophisticated and futuristic approach for genetic testing.
At a few cell embryonic development, DNA sequencing is carried out to determine any defect. Techniques like next-generation sequencing are usually performed for such sensitive testing.
In case of any abnormality, the cells are removed from the embryo, only healthy cells are allowed to grow. It reduces the risk of passing down any genetic defect.
Prenatal genetics is a much-grown field, in comparison with preimplantation genetics. Here genetic tests are carried out directly on the fetus. Fetal samples like amniotic fluid or chorionic villi samples are collected and allowed for testing.
A genetic test is conducted to investigate abnormality or defect at a genetic level. It gives flexibility to parents to abort the fetus in case of having serious congenital abnormalities. For testing chromosomal abnormalities and inherited diseases prenatal testing is advised.
However, there are serious ethical and human rights issues involved in such studies so are restricted or controlled by the government.
Behavioral Genetics simply studies the behavior of an organism. For example, searching for food, the rhythmic finding of nipples in mammals, hyper aggression, criminal mindset, etc. Scientists conduct genetic research to study such traits.
Scientists believe that behavioral traits are governed by some genes or by gene expression. For example, a variant of the MAOA gene is associated with hyper aggression and a criminal mindset.
Noteworthy, behavioral genetics is complex and has a polygenetic base– many genes are involved in the development of a particular type of behavior. And thus difficult to study. I have written two amazing articles on this topic, you can read those here.
Moreover, it is evident that the interaction of genes with the environment plays an important role in developing diverse behavioral traits and patterns but are mostly governed by genotypes. The list of genes and governing behavioral traits are listed below.
|MAOA||Extreme aggression and criminal mindset.|
|SLC6A4||Depression and social cognition|
|DRD4||Impulsive behavior, anger and short temper|
|NRG1||Major role in Schizophrenia|
The genetic foundation of embryonic development is covered in developmental genetics. The interdisciplinary field focuses on the role of genes and gene expressions in fetal development. The major focus of scientists in recent times is epigenetic reprogramming.
On the technical side, the major emphasis of developmental genetics is on how the gene expresses, what genes govern the entire process, the involvement of genes in various developmental stages, genetics of sex determination, genetics of sex differentiation, disomy and genomic imprinting.
The potential output scientists expect from this field is to understand how genes work, the disease develops and expression profile differs during each embryonic stage. Notwithstanding, these are ethical, prenatal and human rights issues associated with developmental genetic studies.
The sub-branch of genetics studies dedicatedly marine life– organisms and ecosystems using genetic techniques and tools. Interestingly, recent research trends suggest that marine genetics would likely help us study the evolution of life from the hydrothermal marine system.
In addition, scientists study the genetics of various organisms including mammals in various marine ecosystems and contribute in preventing their extinction. Economically important and nutrition-rich marine products can be developed too.
It also studies marine ecosystems, interaction and their consequences on mankind and other ecosystems on earth.
Epidemic and Pandemic Genetics:
This is a rapidly evolving field that brings together the discipline of genetics and epidemics and pandemics.
Epidemic and Pandemic Genetics is a very new field. Alternatively saying, just groomed well during the COVID-19 outbreak. It finds the genetic cause of pandemics and epidemics and thereby helps a medical person prevent an outbreak.
Pharmacogenetic studies during the period often led scientists to understand if a drug works against some pathogen or not, whether antimicrobial/antibiotic resistance is developed or not, if so, how it occurs, what alternative drug could be used, etc.
All such studies are conducted during epidemics and pandemics and other than that, most importantly, techniques like sequencing and RT-PCR avail rapid, accurate and mass screening.
Khusbu et at. Studied one novel variant of H1N1 during the 2009 pandemic strain showed antibiotic resistance against Oseltamivir drug- a popular drug given during that time. They have also explained the genetic mechanism of how it occurred.
Statistical Genetics is an alternative field that helps study genetic data and draw quantitative conclusions using statistical methods. For example, genotype frequency, gene frequency or allele frequency.
Such studies have significance in establishing any new genotype and its consequences for a population, another population and an individual. Thus, statistical genetics can be considered an alternative field of population genetics.
Extensive statistical parameters and equations will be explained in some other article.
Neurogenetics studies neurological disorders and their association with genetic factors. Popular neurological disorders like Huntington’s disease, spinal muscular atrophy, spinocerebellar ataxia, etc are studied.
Furthermore, behavioral traits governed by neural systems like hyper aggression, depression, anxiety, etc are also studied. In trends, scientists use genetic tools to study Schizophrenia, depressive disorders, bipolar disorders and neurological, motor, and neuro-developmental disorders.
Conservation Genetics is a complex field that includes biology, conservation, population, and genetic studies for preventing the extinction of any species on earth. In addition, the use of mathematical models, statistical parameters and computational analysis also allows to collect quantitative data regarding the study.
Interestingly, scientists’ studies target organism’s genetics, their genetic diversity, their environment, ecosystem and other factors using genetic tools to understand the cause of extinction and thereby take actionable steps for conservation.
Physiological Genetics brings together the studies of the physiological traits of organisms and genetics. Meaning, how genetic factors contribute to physiological development. Hence, it can be considered as the developmental genetic field.
It often studies genes, gene interaction, expressions, mutations— duplication, deletion or insertion and their consequences on various physiological traits and development. The field of developmental genetics is separately discussed in some other articles, somewhere.
A genetic field that studies biological traits and their consequences are denoted as biochemical genetics. It brings together biochemistry and Genetics. The field focuses on the study of genes that translate various enzymes, their defects and their consequences at the biochemical level.
Put simply, it focuses on genes, governing enzymes and their biochemical outcomes.
Ecological genetics study includes investigations of different ecosystems, abiotic and biotic stress and ecological diversity. It is a combined field of conservation genetics, environmental genetics and marine genetics, etc.
The specialized discipline of Genetics– Quantitative genetics brings into focus the study of qualitative traits like height, weight, etc, and genetic basis. Such traits are polygenic in nature and occur by many genes and their interaction, therefore techniques like whole genome microarrays are used.
Applications of Genetics:
- Characterization and diagnosis of genetic disease
- Identification of pathogenic mutations
- Preserving biodiversity
- Identification and characterization of microbes
- Studying inheritance patterns
- Creating advanced plant species
- Creating genetically modified organisms
- DNA fingerprinting
- Antibiotic resistance study and drug discovery
- Genetic/DNA medicines
- Genetic engineering
- Crop improvement
- Animal and Plant Breeding program
- Infectious disease diagnosis
- Screening, prognosis, and diagnosis of cancer
The sole purpose of writing the present article is to make you understand the concept of genetics and how diverse the field is, thereby developing your interest in genetics depending upon your field of study.
So it’s a career-deciding article, I can say. Genetic tools and technologies are so advanced and as new challenges and problems in various fields arise, scientists use them to solve them. I hope this article will help you in your learning objectives.
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