The human genome is the genome of Homo sapiens, which is stored on 23 chromosome pairs. Twenty-two of these are autosomal chromosome pairs, while the remaining pair is sex-determining. The haploid human genome occupies a total of just over 3 billion DNA base pairs. The haploid human genome contains ca. 23,000 protein-coding genes, far fewer than had been expected before its sequencing. In fact, only about 1.5% of the genome codes for proteins, while the rest consists of non-coding RNA genes, regulatory sequences, introns, and (controversially named) "junk" DNA
The Human Genome Project (HGP) produced a reference sequence of the euchromatic human genome, which is used worldwide in biomedical sciences.
Surprisingly, the number of human genes seems to be less than a factor of two greater than that of many much simpler organisms, such as the roundworm and the fruit fly. However, human cells make extensive use of alternative splicing to produce several different proteins from a single gene, and the human proteome is thought to be much larger than those of the aforementioned organisms. Besides, most human genes have multiple exons, and human introns are frequently much longer than the flanking exon.
Human genes are distributed unevenly across the chromosomes. Each chromosome contains various gene-rich and gene-poor regions, which seem to be correlated with chromosome bands and GC-content. The significance of these nonrandom patterns of gene density is not well understood. In addition to protein coding genes, the human genome contains thousands of RNA genes, including tRNA, ribosomal RNA, microRNA, and other non-coding RNA genes.
The human genome has many different regulatory sequences which are crucial to controlling gene expression. These are typically short sequences that appear near or within genes. A systematic understanding of these regulatory sequences and how they together act as a gene regulatory network is only beginning to emerge from computational, high-throughput expression and comparative genomics studies. Some types of non-coding DNA are genetic "switches" that do not encode proteins, but do regulate when and where genes are expressed.
Identification of regulatory sequences relies in part on evolutionary conservation. The evolutionary branch between the human and mouse, for example, occurred 70–90 million years ago.
So computer comparisons of gene sequences that identify conserved non-coding sequences will be an indication of their importance in duties such as gene regulation.
Another comparative genomic approach to locating regulatory sequences in humans is the gene sequencing of the puffer fish. These vertebrates have essentially the same genes and regulatory gene sequences as humans, but with only one-eighth the "junk" DNA. The compact DNA sequence of the puffer fish makes it much easier to locate the regulatory genes.
ory gene sequences as humans, but with only one-eighth the "junk" DNA. The compact DNA sequence of the puffer fish makes it much easier to locate the regulatory genes
Protein-coding sequences (specifically, coding exons) comprise less than 1.5% of the human genome. Aside from genes and known regulatory sequences, the human genome contains vast regions of DNA the function of which, if any, remains unknown. These regions in fact comprise the vast majority, by some estimates 97%, of the human genome size. Much of this is composed of:
Tandem repeat: Tandem repeats occur in DNA when a pattern of two or more nucleotides is repeated and the repetitions are directly adjacent to each other.An example would be:
in which the sequence A-T-T-C-G is repeated three times.
Interspersed repetitive DNA is found in all eukaryotic genomes. Certain classes of these sequences propagate themselves by RNA mediated transposition, and they have been called retrotransposons.
The major difference of class II transposons from retrotransposons is that their transposition mechanism does not involve an RNA intermediate. Class II transposons usually move by a mechanism analogous to cut and paste, rather than copy and paste, using the transposase enzyme. Different types of transposase work in different ways. Some can bind to any part of the DNA molecule, and the target site can therefore be anywhere, while others bind to specific sequences. Transposase makes a staggered cut at the target site producing sticky ends, cuts out the transposon and ligates it into the target site.
However, there is also a large amount of sequence that does not fall under any known classification. Much of this sequence may be an evolutionary artifact that serves no present-day purpose, and these regions are sometimes collectively referred to as "junk" DNA. There are, however, a variety of emerging indications that many sequences within are likely to function in ways that are not fully understood. Recent experiments using microarrays have revealed that a substantial fraction of non-genic DNA is in fact transcribed into RNA which leads to the possibility that the resulting transcripts may have some unknown function. Also, the evolutionary conservation across the mammalian genomes of much more sequence than can be explained by protein-coding regions indicates that many, and perhaps most, functional elements in the genome remain unknown. The investigation of the vast quantity of sequence information in the human genome whose function remains unknown is currently a major avenue of scientific inquiry.
Author: Dr. Sujata Roy
Rajalakshmi Engineering College, Chennai
Print media are lightweight, portable, disposable publications printed on paper and circulated as physical copies in forms we call books, newspapers, magazines and newsletters. They hold informative and entertaining content that is of general or special interest. They are published either once or daily, weekly, biweekly, monthly, bimonthly or quarterly. Print Media is the oldest form of media. But even today it is growing from strength to strength. Around 4000 small, medium and large newspapers and magazines across the county are registered with the Registrar of Newspapers every year. This indicates that it is a growing sector where employment opportunities are increasing with each passing day. Most of the young aspirants who want to enter the print media prefer reporting, but newspapers and magazines also seek young talent as photographers, artists, editors, computer experts, librarians, and cartoonists. Students who have writing ability, graphics or photo skills, curiosity and deter →
Swachh Survekshan-2017 commissioned by the Ministry of Urban Development during January – February, 2017 aimed at capturing the improvement in sanitation scenario, primarily based on making cities and towns Open Defecation Free and improvement in processing of municipal solid waste. Accordingly, it is outcome oriented. Criteria and weightages for different components of sanitation related aspects used for the Survey are: Solid Waste Management including Door-to-Door collection, Processing and Disposal, ODF status etc: 45% of total 2,000 marks i.e 900 marksCitizen feedback : 30% i.e 600 of total marksIndependent observation : 25% i.e 500 marks List of the cities and their rank Ranking City State 1 Indore Madhya Pradesh 2 Bhopal Madhya Pradesh 3 Visakhapatnam (Vizag) Andhra Pradesh 4 Surat Gujarat 5 Mysuru (Mysore) Karnataka 6 Tiruchirappalli (Trichy) Tamil Nadu 7 New Delhi Municipal Council (NDMC) Delhi 8 Navi Mumbai →
Micro Credit is defined as provision of thrift, credit and other financial services and products of very small amount to the poor in rural, semi-urban and urban areas for enabling them to raise their income levels and improve living standards. Micro Credit Institutions are those which provide these facilities. What is a Self-Help Group ? A Self-Help Group (SHG) is a registered or unregistered group of micro entrepreneurs having homogenous social and economic background, voluntarily coming together to save small amounts regularly. They mutually agree to contribute to a common fund and to meet their emergency needs on mutual help basis. The group members use collective wisdom and peer pressure to ensure proper end-use of credit and timely repayment thereof. In fact, peer pressure has been recognized as an effective substitute for collaterals. →
Genetic Modification Genetic modification refers to techniques used to manipulate the genetic composition of an organism by adding specific useful genes. A gene is a sequence of DNA that contains information that determines a particular characteristic/trait. All organisms have DNA (genes). Genes are located in chromosomes. Genes are units of inheritance that are passed from one generation to the next and provide instructions for development and function of the organism. Crops that are developed through genetic modification are referred to as genetically modified (GM) crops, transgenic crops or genetically engineered (GE) crops. Over the last 30 years, the field of genetic engineering has developed rapidly due to the greater understanding of deoxyribonucleic acid (DNA) as the chemical double helix code from which genes are made. The term genetic engineering is used to describe the process by which the genetic makeup of an organism can be altered using “recombinant DNA technology.” This →
If you want to contribute your content to our site. Please mail us your content to firstname.lastname@example.org