Chromosome jumping

It helps in isolating the non-contiguous clones from a genomic library. These clones skip a region between the known points on a chromosome. Chromosome jumping acts as a tool for bypassing the regions that do not allow the cloning process. It plays a crucial role in physical mapping techniques for generating genomic markers. Chromosome jumping helps in searching for a specific gene. The regions difficult to clone include certain repetitive sequences. It helps in analyzing the sequences separated by more than 100-kilobases. Chromosome jumping involves two alternative procedures. The first method uses rare cutting enzymes. The second method uses frequent cutters. Chromosome jumping is also known as chromosome hopping. Consider the phage DNA.

A method using the rare cutters:

These cutters belong to the class of endonucleases. The first step involves the isolation of the genomic DNA. The isolated DNA gets a treatment with the restriction enzyme (rare cutter). The process is known as restriction digestion. It allows the isolation of fragments with 100 kb sizes. These fragments get subjected to a specialized electrophoretic technique known as the pulse field gel electrophoresis. The separated fragments get easily circularized later on. This method gives rise to three types of fragments. The first type includes the fragments having sequences with 100-kilobase sizes. The second type of fragments includes sequences of the original augments with lighted sequences such as the junction fragments. The third type of fragments includes other types of genomic sequences.

A method using frequent cutters:

The frequently cutting endonucleases lead to partial digestion of the fragments. First, the genomic DNA gets isolated from the sample. Next, the restriction enzymes carry out partial digestion of the genomic DNA. The fragments obtained from the partial digestion get selected based on the size. The next step involves the pulse field gel electrophoresis. The fragments obtained from the pulse field gel electrophoresis get cloned into a suitable vector.

Cloning:

The fragments obtained from both the procedures get cloned into a suitable vector with the presence of a selectable marker. The vector gets introduced into the host such as E. coli bacteria. After this, the cells get plated on a medium to check the growth of the plaques. The bacteriophages genome having the selectable marker gets replicated to form the plaques. They are known as the jumping clones. Next, the jumping fragments get identified through the nucleic acid hybridization. It involves using a specific probe. Thus, it is possible to identify the fragments undergoing repetitive hopping process.

Image: Chromosome jumping library depicting jumping clones

Chromosome jumping library:

It includes a collection of recombinant molecules obtained through chromosome jumping. The two types of jumping libraries include the general jumping and the specific jumping libraries. The general jumping libraries include sequences starting at any genomic locations. They travel to specific distances. These libraries involve sequences obtained from chromosome jumping involving frequent cutters. The specific jumping libraries show a specific jumping of the clones. They jump from the rare restriction site to the adjacent restriction sites. These libraries involve sequences obtained from the chromosome jumping methods using the rare cutters. The examples include libraries constructed using Not-I restriction endonucleases. Thus, with the help of chromosome jumping libraries, the clones jump from one restriction site to the other.

Chromosome jumping libraries have many applications. They include prenatal diagnosis, de novo assembly, and characterizing chromosomal rearrangements. Highly efficient bacterial genome assemblies were constructed using long jump chromosome libraries. The whole genome jumping library offers a gene-level resolution. Thus, it is beneficial for prenatal diagnosis and testing. A short jump library gets created using ligation of the DNA fragments with biotinylated, followed by circularization and affinity assays. However, it is less efficient due to its reduced genome coverage. Long jump library is efficient for longer DNA fragments. Another type of chromosome jumping library known as custom barcode jumping library distinguishes the junction fragments very efficiently. The E. coli vector transfection helps in amplifying larger DNA fragments in the Fosmid-jump library.

Enzymes used in chromosome jumping:

An endonuclease enzyme shows capability in cleaving the phosphodiester bond in the DNA strand. The technique of chromosome jumping involves restriction enzyme such as endonuclease type-II. These enzymes efficiently cleave longer DNA sequences. The following table depicts the examples of endonucleases used in chromosome jumping:

Endonuclease	Restriction site
Not I	GCGGCCGC
Sfi I	GGCCNNNNNGGCC
Pac I	TTAATTAA
BssHII	GCGCGC

Table: Endonucleases used in chromosome jumping and their restriction sites

Certain regions in the mammalian genome show the presence of rare nucleotide repeats. Such regions also get considered through enzyme treatment.

Genetic disorders arise due to defective genes or mutations. However, certain genetic disorders, the mutant genes or the gene products remain unidentified. In such cases, it becomes difficult to know the exact details of the genes and the pathways involved. Thus, identifying these genes and cloning them becomes the most difficult task. Also, the molecular markers prove to be inefficient in identifying such genes. The reason involves very large molecular distances. Reverse genetics is a subfield of genetics involving investigation of a gene or a protein function. The first step involves directed mutagenesis using the knowledge of a DNA or a protein sequence. Next, the programmed mutations get introduced back to the genome. However, it is difficult to identify the unknown sequences responsible for causing a genetic disorder. The problem could be solved using a chromosome jumping library. A review mentioned the chromosome jumping library constructed for the cloning of DNA sequences. These sequences lie a hundred kilobases away from the gDNA start point.

References:

[1] Encyclopedia of Genetics, Genomics, Proteomics, and Informatics, by George P. Rédei

[2] The Dictionary of Genomics, Transcriptomics, and Proteomics, By Guenter Kahl

[3] Plant Chromosomes, by Archana Sharma

[4] Introduction to Plant Biotechnology, by H. S. Chawla

[5] Molecular Biology and Genetic Engineering, by P. K. Gupta

Copyright, 2019, Study Genetics Online

The Study of Developmental Genes in Drosophila

Small, cute looking fruit flies known as Drosophila, fly around the leftover foods, fruits, vegetables, and juicy substances. Never thought about these flies helping the scientists tremendously in the genetics research. Drosophila, one of the most important model organisms, is used worldwide in various experiments. Drosophila is one such genus of the flies that contains more than 900 described species. Hence, it is the most extensively studied organism in the fields of cytology and genetics. Most of the genetic information available today involves data extracted from Drosophila melanogaster studies. Thousands of mutants are available with this insect. Many of the mutants affect the developmental processes. These genes provide a rich array of information through developmental genetics. The mutants helped us in understanding sex determination and many other traits.

                                                                  Image 1: Drosophila (fruit fly)

 The specialty of using fruit flies as model organisms lies in their ability to reproduce on any media. Obtaining Drosophila cultures is not a tough job. It grows on almost all the foodstuffs. Just take a container having holes for the air to pass inside. Put a piece of banana or any juicy fruit inside it and keep it in your window. After some time, these tiny fruit flies get attracted to the fruit inside the container. Another important specialty of Drosophila lies in the presence of a polytene chromosome, widely used in gene studies. The eukaryotic development completely depends on the precise regulation of a group of genes. The genetic regulation of the development in Drosophila progresses significantly. An important point to be noted regarding the developmental genes in Drosophila is that these flies have counterparts in all the organisms, including humans. The body structure of Drosophila involves many segments. Homeotic genes determine the developmental identity of these segments. Studying the genes accelerates the developmental analysis. Thus, in layman terms, the developmental genetics involves the study of mutations deciding the developmental processes gaining the information of the way normal genes get control over the growth, form, behavior, and reproduction. A well-differentiated organism arises from a single cell. Zygote forms due to the fusion of sperm and egg. The cell exhibits totipotency or a potential to develop into any cell type. The genetic programming determines the fate of the cell. This process is known as cell determination. It, later on, involves differentiation, meaning, the determined cells undergo developmental programs and synthesize specific types of cells. Then morphogenesis comes into the picture.

Developmental stages in Drosophila:

A well-ordered sequence of developmentally programmed events follows a strict genetic control. Particular molecular gradients get established before fertilization. There is a region known as polar cytoplasm at the posterior end. The fertilized egg consists of two parental nuclei that fuse to produce a diploid zygote nucleus. It undergoes nine divisions in the cytoplasm and gives rise to multi-nucleate syncytium. The syncytial blastoderm nuclei further migrate and divide, thereby producing a layer at the egg periphery. The nuclei then divide four times resulting in instructions making other important cellular structures such as membranes. After these events, the initial steps in the embryonic development include axes formed in a tight genetic control.

The segment pattern of the embryo involves an adult segment organization. The development of the body structure includes two main processes. The four axes studied in a Drosophila egg include anterior, posterior, dorsal and ventral axes. Along these axes, a molecular gradient occurs. Expression of genes depends on the position of a nucleus involving the intersecting gradient specific region in the adult body. Study of genes involves a cellular blastoderm. Hence, they are known as Para segments. After ten hours or so, these Para segments further look clear and appear like segments. The maternal genes controlling the development of anterior, posterior and dorsoventral axes determine them. Before fertilization, the genes get expressed outside the egg of the mother fly. A wide number of genes get expressed such as Bicoid, Swallo, Oskar, Torso, and Cauda.  The genes express themselves by coding for transcription factors.

The products of these genes, when carried to the egg, establish gradients consisting of RNA and proteins distributed differentially. 

The following table describes the genes and their functions:

Name of the gene	The function of the gene
Bicoid	Involved in axial patterning
Swallow	Plays an important role in bicoid message localization
Oskar	The gene defines a posterior pole (early embryogenesis)
Torso	Determining the anterior and posterior terminal structures.
Caudal	Segmentation of the embryo
Snake (snk)	Extracellular signaling component
Easter	Required for the development of all lateral and ventral pattern elements.

Table 1: Developmental genes and their functions.

Image 2: Development of segments in Drosophila

1.   Formation of embryo axes:

As discussed, there are anteroposterior and dorsoventral axes. The anteroposterior axis requires regulation of Bicoid, Nanos, Acron, Telson, and Torso. Bicoid gene determines the anterior end. It encodes for a mRNA translating to a protein consisting of a helix-turn-helix protein. Mutation in this gene leads to the formation of an embryo lacking a head and the thorax. The Nanos class of genes determines the posterior end of the abdominal segments of the embryo. Further classification of the anterior and posterior structures involves most anterior and most posterior structures respectively. A separate set of genes regulate them.

The dorsal gene involves a product forming ventral to the dorsal gradient in the syncytial blastoderm. The bicoid gene, a key maternal effect gene involves a product forming anteroposterior axes. The bicoid gene encodes a protein known as a morphogen which controls the development. The bicoid gene affects the expression of the caudal gene. After the translation of the bicoid mRNA, the formation of the caudal protein gradient occurs. The protein is lowest at the anterior end and highest at the posterior end. The behavior of the caudal protein antagonizes the behavior of the bicoid protein. The segmentation phase involves the caudal protein. One more maternal effect gene known as Nanos gene helps to form posterior structures. The Drosophila with null mutations in the Nanos genes exhibits phenotype with no abdomen. A hunchback gene expresses a hunchback protein. This protein correctly carries out the developmental processes. It decreases from the anterior to the posterior.  The Nanos gene product increases from anterior to posterior. It is highest at the posterior end.

Antero-posterior structure
Anterior end	Posterior end
Caudal protein: It is lowest at the anterior end and highest at the posterior end.	Hunchback protein: It is highest at the anterior end and lowest at the posterior end.
Morphogen protein It is highest at the anterior end and lowest at the posterior end.	Nanos protein: It is lowest at the anterior end and highest at the posterior end.

Table 2: Proteins playing a crucial role in the development of the anterior and the posterior end.

2.   Segmentation genes:

These genes determine the embryonic and adult segments. Mutations in these genes alter the number. Three main genes include gap genes, pair-rule genes, and segment polarity genes. The homeotic genes specify the identity of the genes. Gap genes include Kruppel, Hunchback, Giant, and Tailless. All these genes encode transcription factors. Pair-rule genes include Hairy, Even-skipped, Runt and Fushi Tarazu genes encoding transcription factors. Engrailed gene is an example of the segment polarity gene. The gap genes divide the embryo into broad regions. The pair-rule gene divides the embryo into seven segments along the craniocaudal axis. The segment polarity genes divide the embryo into fourteen segments.

3.   Determination of the regional characteristics:

The regional characterization of the individual segments in the embryo involves an important group of genes known as homeotic genes. These genes determine whether the embryonic segment bears antennae, legs or wings. Chromosome 3 consists of a total of eight homeotic genes arranged in Antennapedia Bithorax groups. They encode 60 amino acids. Other genes involved in the regional characterization include Antennapedia complex, Bithorax complex and Ultrabithorax complex. Hence, the study of the developmental stages involves a wide variety of mutants. The genes control the development in a temporal regulatory cascade. Hence, studying the developmental genes in Drosophila helps in comparison with the higher organisms.

References:

[1] Genetics, Daniel Hartl, Maryellen Ruvolo

[2] Medical Genetics, G.P. Pal

[3] Drosophila embryogenesis, Wikipedia

[4] Drosophila and the Molecular Genetics of Pattern Formation: Genesis of the Body Plan, NCBI

[5] Homology, Genes, and Evolutionary Innovation, Günter P. Wagner
[6] IGenetics, Peter Russell, second edition

© Copyright, 2018 All Rights Reserved.

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Medical Genetics

Genetics plays an important role in the field of medical sciences. There arises a genetic base to a disease, the development, reproduction, and other processes in the body. The gene or a blueprint of life occurs in every cell and is an important inheriting factor. Hence, it is important to understand genes and their role in various diseases, cancers, developmental stages, and interactions with various components. Some of the genes encode for proteins. The genes get passed on from one generation to the next generation. They also carry any minute changes or mutations. The diverse population is a sign of variation. Due to recent advances in health research, more and more diseases showed a genetic base. The science of genetics helps in detecting many diseases. It helps in their treatment or prevention. When you try to understand the molecular intricacies of the genetic material, you will be amazed to see an entirely different world. Thousands of reactions keep occurring at a molecular level.

DNA, the blueprint of life consists of nucleotide base pairs attached to the phosphodiester bonds. Small units of DNA form genes and exhibit specific functions. Various disorders arise due to gene mutations. Hence, they are known as genetic disorders. Detection of genetic disorders involves modern genetic diagnostic techniques. There involves the tremendous importance of genetics in medical sciences. To understand its role in health and disease, we must know the basic concept of genetics. 

The review covers the following topics in detail:

1.     What are genes and various branches of genetics?

2.     Chromosomes and disorders associated with the genes

3.     Disorders inherited due to faulty genes

4.     The role of gene mutations in biochemical disorders

5.     Detection of genetic disorders

6.     Genetic counseling

7.     Gene Cloning and DNA analysis

8.     Gene therapy

Image 1: Medical genetics

Various branches of genetics:

Human genetics involves several branches such as cytogenetics, molecular genetics, biochemical genetics, cancer genetics, Immunogenetics, and developmental genetics. Cytogenetics is the study of chromosomes and various disorders associated with the same. A chromosome is a specialized structure consisting of DNA-protein complex packed in a condensed manner. Cytogenetic techniques help in studying these structures. Molecular genetics involves the study of genes at the molecular levels such as single base pair changes, mutations, and other studies. Biochemical genetics involves genes controlling the enzyme production. Cancer genetics involves studying cancer genes and mutations associated with cell cycle control. Different antigen-antibody interactions studies involve immunogenetics. Developmental genetics helps to study the genetic control of the development. Hence there are many such branches of genetics. The field of genetic science is very vast. Half the rate of first trimester abortions involves chromosomal abnormalities. Congenital malformations, childhood blindness, deafness, and mental retardation mostly occur due to gene mutations.

Chromosomes and disorders associated with the same:

Every cell in the human body constitutes chromosomes. The chromosome complement in humans consists of autosomes and sex chromosomes. There are 22 pairs of autosomes and a pair of sex chromosomes. They are known as X and Y chromosomes respectively. A normal male has 22 pairs of autosomes, an X, and a Y chromosome. A normal female has 22 pairs of autosomes and two X chromosomes. Karyotyping involves arranging the chromosomes as per the groups resulting in a photomicrograph. This photomicrograph or a karyotype consists of autosomes and sex chromosomes arranged in groups. Structural and numerical abnormalities in the chromosomes result in genetic disorders. They are known as chromosomal anomalies or chromosomal abnormalities.

Disorders due to an abnormal number of chromosomes are known as numerical anomalies. They arise due to non-disjunction of chromosomes. Monosomies (one chromosome less), trisomies (one chromosome extra), and many other conditions consist of chromosomal anomalies. Down’s syndrome is an example of trisomy. It occurs due to trisomy of the 21^st chromosome. Disorders associated with the structural abnormalities of chromosomes are known as structural anomalies. Deletions, duplications, inversions, and translocations arise due to the structural anomalies of the chromosomes. They also result in conditions such as mosaicism.

Disorders inherited due to faulty genes:

Monogenic or single gene disorders are the genetic disorders arising due to the inheritance of a mutated gene. Two main types of inheritance include autosomal inheritance and sex-linked inheritance. Autosomal inheritance involves autosome related disorders or traits. Inheritance of the traits due to the expression of genes present on the sex chromosomes is known as a sex-linked inheritance. Autosomal dominant inheritance manifests the trait even if the mutant gene occurs in a single dose. For example, Huntington’s disease arises due to abnormal CAG nucleotide repeat. Autosomal recessive inheritance manifests the trait even if the gene is present in the double dose (homozygous). An example includes sickle-cell anemia. Sex-linked inheritance is either X-linked or Y-linked. The X-linked inheritance occurs in a dominant or a recessive form. Very few cases report Y-linked inheritance.

Polygenic or multifactorial inheritance depends on many genes. The traits are known as quantitative traits and depend on many factors. Abnormalities in mitochondrial DNA (mtDNA) occur due to mitochondrial inheritance. The genes do not behave as dominant or recessive in polygenic inheritance. They exhibit an additive effect on the trait.

Biochemical genetics:

This area of genetics deals with the genetic control of the metabolic pathways. According to the one gene-one enzyme hypothesis proposed by Beadle and Tatum, metabolic processes occur in various steps controlled by enzymes. Each enzyme gets coded by one gene. Inborn error of metabolism arises due to enzyme unavailability or insufficiency occurring as a result of related gene mutations. The inborn error of metabolism follows Mendelian inheritance pattern. PKU, a classic example of the inborn error of metabolism, arises due to the deficiency of phenylalanine hydroxylase.

Image 2: The role of genetics in medicine

Detection of genetic disorders:

Cytogenetic and molecular genetic studies or tests detect various anomalies. The prenatal diagnosis helps to detect abnormalities in the fetus before birth. Examples of prenatal tests include Amniocentesis, chorionic villus sampling, fetoscopy, ultrasonography, maternal serum screening, and fetal blood sampling. Non-invasive prenatal tests also help in detecting the fetal DNA through maternal serum testing. Karyotyping helps to detect chromosomal abnormalities. FISH and other hybridization techniques detect minute changes in the DNA. SNP genotyping involves PCR, agarose gel electrophoresis, and gel documentation systems.

Genetic counseling:

It is a specialized session with a genetic counselor. The genetic counselor is an expert in genetics and a trained professional who guides the couples and patients suspected with the genetic disorders. Genetic counseling helps in the risk assessment of hereditary diseases, repeated abortions, and stillbirth cases. It also helps in reducing the risk of having a baby with the genetic and other ailments including the inborn errors of metabolism.

Gene cloning and DNA analysis:

Gene cloning involves cloning the gene of interest for incorporation into the desired vector. It has a wide range of applications in recombinant DNA technology. It helps in expressing the desired products such as proteins, vitamins, and other molecules. Peptide vaccines and hormones get developed using gene cloning. DNA analysis using techniques such as DNA fingerprinting help to solve parental issues. Analyzing DNA and genotyping techniques help in detecting gene mutations.

Gene therapy:

It helps in replacing the gene that has lost its function. The first step involves defective gene identification and cloning the normal gene in place of the defective gene. The normal gene insertion includes a vector. The first gene therapy gained success in case of a child having ADA deficiency associated with severe combined immunodeficiency syndrome (SCID). 

References:

[1] Emery’s elements of Medical Genetics, Peter D. Turnpenny

[2] Chromosome Abnormalities and Genetic Counseling,  R.J. MKinlay Gardner, Grant R Sutherland, Lisa G. Shaffer
[3] Medical Genetics, G. Bradley Schaefer, James N. Thompson

Copyright, 2018 All Rights Reserved

Top 10 Model Organisms

Conducting trials directly on humans is forbidden on humanitarian grounds. Since the human body is very complex direct involvement of humans as subjects of experiments may not always be possible. Therefore it is ideal to use prokaryotes, eukaryotes, and organisms other than humans. These helper organisms are known as model organisms. They contribute to scientific and industrial research. These organisms include bacteria, fungi, viruses, algae, nematodes, worms, and higher animals. Model organisms are selected based on criteria such as their ease of growing, short life cycle, well-defined cellular structures, easily analyzable properties, safe and ethically sound. Using hazardous toxin-producing bacteria or organisms for conducting experiments is forbidden and is accessed only in rare and unavoidable cases. Only trained, well-qualified professionals handle these organisms. Model organisms are involved in genome analysis, recombination experiments and sequence similarity studies. It requires a lot of care and caution to handle these organisms. Recombinant vaccines, peptides, and biomolecules are produced using model organisms. Biosatellites and spaceships use model organisms in their first launch.

1.   Yeast:

Yeast is a very useful eukaryote with beneficial properties. Yeast is very easy to culture because it can easily grow on fruits, sugary and salty foods. It can easily proliferate from 12⁰C to 40⁰C. The environment of acidic to alkaline is suitable for its growth. Beer and wine industry widely make use of yeast. Preparation of bakery products also involves yeast. Division of yeast occurs due to a process is known as budding. Yeast cells are easy to study since yeast is a single-celled organism. In addition to studying yeast cells with ease, these cells are comparatively safe to handle.

Most of the experiments in genetic engineering and genome research involve the use of yeast as a model organism. It is possible to study cell cycle, DNA replication, protein and cell wall synthesis using yeast cells. Gene cloning can be achieved using vectors. Yeast artificial chromosomes (YACs) are yeast cloning vectors. Typical features of YACs include telomere (TEL), centromere (CEN), selectable markers on each arm, an origin of replication, and restriction sites or multiple cloning sites. YAC vectors can accommodate DNA fragments of several base pairs. Protein-protein interaction studies make use of the yeast two-hybrid system. Cancer genetic studies also involve yeast as model organisms.

2.   Fruit fly:

Most of the genetics experiments involve the use of the fruit fly. It is scientifically known as Drosophila melanogaster. Drosophila is easy to grow since it does not require any specific conditions to grow. It can grow on a wide range of foodstuffs right from a piece of banana to a culture medium. There is a wide range of mutants observed in the fruit fly. Studying its genes is simpler as compared to other organisms. Drosophila is used to study developmental genes, mutant genes, and chromosomes. Morgan was the first scientist to use this model organism. The generation time of fruit fly is rapid as it takes less than two weeks to grow. Transgenic fruit flies are those that consist of foreign gene(s) inserted into their genome.

Drosophila is one such genus of the fruit flies that contains over 900 described species. The genic balance theory was used to identify the concept of sex determination. This theory worked out primarily in Drosophila. According to this theory, sex determination is the ratio of sex chromosomes and polytene chromosomes. A polytene chromosome is a giant chromosome in Drosophila produced by the endomitotic process. It consists of many chromatids. DNA replication and heterochromatin studies are carried out using Drosophila polytene chromosomes. They are also involved in gene mapping and linkage studies. The fruit fly is a model system for understanding human biology and disease. Findings suggest that this model organism has homologs for 177 out of 289 genes involved in human cancers.

Image: Model organisms

3.   E.coli:

Escherichia coli are most widely used bacteria in the biotechnology industry. Genetic engineering principles make very high use of this bacteria for cloning and other experiments. The life cycle of E. coli is simple to understand. Hence they are easy to grow and safe to handle. These bacteria consist of extrachromosomal material known as plasmids. Genetic modifications are possible with this model organism. E.coli can be engineered to produce the desired product. For example, gene modification helps in synthesizing insulin. Plasmid cloning vectors include pUC 19 vectors that contain multiple cloning sites. Important applications in model organisms are as follows:

a.    Gene cloning experiments: Pure samples of cloned DNA are obtained using plasmid vectors. Some of the plasmids with multiple cloning sites enable different types of restriction enzymes to act on them.

b.   Bacteriophage studies: The viruses that infect the bacteria are known as bacteriophages. They follow lytic as well as the lysogenic cycle of infection.

c.     Gene mapping: E.coli bacteria undergo a process of conjugation for transferring genes from one bacterium to another. Thus, gene mapping is possible with the help of conjugation experiments.

d.    Study of DNA replication: Prokaryotic DNA replication study involves E. coli as a model organism.

e.     Identification of mutant phages: E. coli are used to identify mutant phages in site-directed mutagenesis.

f.       Bacterial Artificial Chromosomes (BACs): They are useful for cloning DNA fragments in E. coli. BACs consists of an origin of replication, multiple cloning sites, a selectable marker, and other features.

4.   Nematode C. elegans:

Caenorhabditis elegans is the widely used nematode in zoology. This nematode exhibits anatomical simplicity. It is ideal to carry out gene diversity and cell cycle studies with this organism. The life cycle of this nematode is just three days. Early embryonic genes are clear to study with this organism. It is capable of learning simple tasks. C elegans is used to study the genetic and molecular aspects of embryonic development, morphogenesis, nerve systems, aging, and behavior.

5.   Arabidopsis thaliana:

It is a small plant popular for studying genetic analysis. A complete genome sequence of A. thaliana is available. It is useful to understand processes including nutrient transport and flower development. CRISPR/Cas 9 gene editing also utilizes this plant.

6.   Mus musculus:

The gene content in mice is similar to that of humans. The genome sequence of mice is known to us. Mouse models are used to study organ and immune systems. Mice are just like humans in developing diseases such as cancer, diabetes, atherosclerosis, hypertension and Alzheimer disease. Thus mouse models are far better to work. The mice help in studying various gene mutations, biochemical pathways, metabolism, pharmacokinetics, and pharmacodynamics. Thus, they are ideal for clinical trials and research.

7.   Neurospora crassa:

It is a haploid fungus widely used in cellular processes. It is possible to grow this strain and use it for tetrad analysis. Typical findings using this model organism involve centromere distance, crossing over and poky mutants. The recessive traits easily show up in the offspring. Thus it is simple to study genetic analysis.

8.   Danio rerio:

The common name for Danio rerio is zebrafish. It is a model organism in stem cell biology and developmental genetics. Its embryos are transparent and help in clearly identifying stages of development. It is easy to feed zebrafish by making a genetic cross.

9.   Lambda bacteriophage:

It is a phage that infects E. coli cells. It replicates using bacterial machinery. A bacteriophage is an important tool for genetic analysis. It is a model system for studying genetic recombination, complementation, and cloning experiments. The lambda genome is capable of insertion into the bacterial chromosome.

10.                      Cavia porcellus:

The common name for this model organism is the guinea pig. However, this organism is not a pig but a rodent. Germ theory was established using guinea pigs as model organisms. They are used to study infectious diseases such as cholera, typhus, and brucellosis.

References:

[1] Biotechnology, David P. Clark, Nanette J. Pazdernik

[2] Introduction to Genetic Analysis, Anthony J.F. Griffiths, Susan R. Wessler, Richard C. Lewontin, Sean B. Carroll

[3] Genetic Analysis: Genes, Genomes, and Networks in Eukaryotes, Philip Mark Meneely

[4] Encyclopedia of Genetics, Eric C.R. Reeve

[5] Neurospora: Contributions of a Model Organism, Rowland H. Davis
[6] Model organisms- Wikipedia

© Copyright, 2018  All Rights Reserved