Genes are Functional Units. That means that genes are not microscopically visible, like the chromosomes or the chromatine. Geneticists divided the DNA into groups of nucleotides that code for one single protein. This is called a gene.
Genes can contain from 1,000 to more than 1.5 million nucleotides (or base pairs) depending how large the protein they are coding for are. This protein is Titin. It consists of 27,000 amino acids.
The human genome project was completed in 2003. It was established that human genome contains about 20,000 to 25,000 genes. Journal Nature 2003
Only 1.1% to1.4% of the genomes sequences code for proteins. Exons are coding regions, Introns are non-coding regions.
Non-coding regions are initially copied into RNA, but they are left out of the final RNA version (reason unknown).
About 10% of the genes in the human genome encode for DNA binding proteins(regulatory proteins). Some of these proteins recognize and attach to specific bits of DNA to activate gene expression (ex. transcription factors, polymerases, nucleases)
A genetic variation is a permanent change in the DNA sequence that makes up a gene. Most variants are harmless or have no effects at all. However, other variations can have harmful effects leading to disease.
Some genetic variations affect only a single gene. Single gene mutations are responsible for many rare inherited neurological diseases. For example Huntington’s disease is a result of what is called an expanded “triplet repeat” , a stutter in the huntingtin gene sequence.
In the huntingtin gene, triplet repeats of 20 to 30 times are normal and cause no symptoms. In people with Huntington’s disease, the number of repeats reaches 40 or more. The mutation creates an abnormally shaped protein that is toxic to neurons. As cells start to die, the symptoms of Huntington’s disease appear. They consist of uncontrollable writhing movements of the legs and arms, a loss of muscle coordination, and changes in personality and thinking.
Some cases of Lewy body dementia have been linked to having two or morecopies of the SNCA gene.This gene encodes a protein called alpha-synuclein.The excess alpha-synuclein accumulates inside the brain cells, jamming thecells’ machinery.
Some diseases show familial clustering but do not conform to any recognized pattern of single gene inheritance. They are termed multifactorial or complex disorders. Multifactorial or complex disorders depend on many genes and the environment.
Geneticists search for connections between genes and disease risk by performing three kinds of studies: Linkage Studies (using DNA or RNA) Genome Wide Association Studies (using DNA) Gene Expression Profiling (using RNA)When a DNA or RNA portion is presumed to contain asusceptibility locus for a disease, that area is red nucleotideby nucleotide. This process is called DNA or RNA sequencing.
Regardless of which study is used, the end result is DNA or RNA sequencing. For thispurpose a device called a microarray, is employed. This is a small chip ( a gene chip),coated with row upon row of DNA or RNA fragments.
Sequencing was once a time-consuming and expensiveprocedure, but a new set oftechniques called next-generation sequencing hasemerged as an efficient, cost-effective way to get a detailedreadout of the genomeFor ex. the Lindsays approachhas the potential to sequenceDNA at a speed of hundreds tothousands of base pairs persecond.
In laboratory, GWA studies and gene expression profiling studies are leading to insights into new possibilities for disease prevention, diagnosis and treatment. When geneticists identify a gene or gene regulatory pathway associated with a disease, they uncover potential new targets for therapy. Understanding the relationship between genes and complex diseases also is expected to play a role in personalized medicine. One day a microarray-based genome scanning could become a routine way to estimate a person’s genetic risk of developing diseases like stroke, Alzheimer’s disease, Parkinson’s disease and certain brain cancers. Also researchers hope to develop customized drug “cocktails” that are matched to a person’s unique genetic profile. Researchers believe that these customized drugs will be much less likely than current medicines to cause side-effects.