On the basis of position of centromere:
Chapter 1 : Introduction to Genetic Engineering
“An inherited factor which determines the biological characters of an organism”
The term “gene” was used for the first time by Johannsen (1909).
According to him, “genes are the functional units of life found on chromosomes.”
Each gene occupies a specific position on a specific chromosome; this position is called “locus.”
Genes determine the physical and physiological characteristics of the organism.
Benzer has proposed a model to explain the structure of genes. According to this model, a gene is composed of the following parts:
Topics covered in this snack-sized chapter:
- Cistron: the functional unit of gene, each unit of which is responsible for a product; the structure of gene which synthesizes a polypeptide chain, may be composed of 30,000 nucleotides
- Muton: the smallest unit of DNA which could undergo mutation; thus, it is a unit of mutation, generally composed of one or more nucleotides
- Recon: the smallest unit of DNA capable of undergoing crossing-over and recombination; may consist of one pair of nucleotide
- Operon: a group of structural and controller genes which control catabolism genetically
The term “chromosome” was introduced by Waldeyer (1888) for the darkly stained individualized bodies located in the nucleus.
Organized structures of DNA and protein found in cells
A single piece of coiled DNA containing many genes, regulatory elements and other nucleotide sequences
Our body cells have 23 pairs of chromosomes. In each pair, one chromosome comes from your mother and one from your father.
On the basis of number of centromeres:
- Replicon: the unit of replication
Number of Cetromeres
Position of Centromere
Near centre (sub-median)
J or L shaped
Two un-equal arms
Near at one end (sub-terminal)
One arm very short and another long
Special types of chromosomes are found in certain eukaryotic cells and these chromosomes similar to their name are found to be different from the other chromosomes and are present in certain specialized cells.
They are found to be very large in size and hence they are also called giant chromosomes. They are of two types:
The simple addition, deletion, or manipulation of a single trait in an organism to create a desired change.
Genetic engineering is one of the most important technologies now available to scientists.
Genetic Engineering, the process of extracting DNA from one organism and combining it with the DNA of another organism, thus introducing new hereditary traits into the recipient organism.
- Polytene or Salivary Gland Chromosome
This technique involves following steps:
- The gene of interest is isolated from the DNA molecule using the restriction enzymes
- After isolation, the gene is inserted into a vector and is cloned to make multiple copies of gene of interest
- When the cloning is done, is incorporated into the plasmid
- Now the gene or DNA along with plasmid is called “recombinant DNA”
In this method, pores are created in the membrane of the cell and genes can be transferred easily.
Special chemicals are used to make pores in the cell surface.
Sometimes cells are exposed to weak electric current; it also makes pores in the surface of the cells and genes can easily pass through these pores.
Electro and chemical poration
Other methods do not rely on biological vectors like plasmids and viruses.
One of these is called “microinjection” and involves simply injecting genetic material containing the new gene into the recipient cell.
Where the cell is large enough, as many plant and animal cells are, the injection can be done with a fine-tipped glass needle.
Somehow the injected genes find the host cell genes and incorporate themselves among them.
Small silver particles are used to insert the genetic material into the recipient cell
These silver particles are coated with the genetic material and, when released in the cell, genetic material incorporates with the genes of the host cell.
In one projectile method, shot gun is used to insert the silvers into the host cell.
Genetic engineering can be employed to treat human diseases by manipulating the disease genes.
First human insulin developed by using the techniques of genetic engineering; insulin is the special component of the body and lack of this component causes diabetes
Gene therapy is used for medical purpose, to replace the defective genes with the healthy genes during the genetic and other diseases; many heart and autoimmune diseases have been treated by using gene therapy.
In the field of medical treatment
Using the techniques of genetic engineering, agriculturists have succeeded in making pesticides and insecticides which protect the plants against pests and insects and help grow the plant quickly.
Genetic engineering technology has been employed effectively in the creation of genetically modified foods that have superior yields with high nutritional value.
Increases the efficiency of photosynthesis, increasing the resistance of the plant to salinity and also reducing the plant’s need for a nitrogen fertilizer
In the field of agriculture
Genetic engineering has enabled the pharmaceutical industries to make such drugs which fight against the diseases efficiently.
Could be used to replace the damaged heart cells by heart attack with normal clone cells
Could enable a sterile woman to have a child derived from her own body, by using any cell from her organism
Genetically modified plants and animals have the potential to replace traditional farming or poultry. This will result in destruction of economies based on these products.
Newly introduced genetically modified organism may destroy food chains and damage food webs.
Genetically modified ingredients can cause cancer.
It would be costly.
Misuse of this technology in the production of biological warfare or weapons is a very major disadvantage.
Prospect of creating new species might create natural imbalances especially on the habitats and feeding habits of other animals. This may affect the biodiversity.