A gene is the basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions to make molecules called proteins. However, many genes do not code for proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases. An international research effort called the Human Genome Project, which worked to determine the sequence of the human genome and identify the genes that it contains, estimated that humans have between 20,000 and 25,000 genes. Show Every person has two copies of each gene, one inherited from each parent. Most genes are the same in all people, but a small number of genes (less than 1 percent of the total) are slightly different between people. Alleles are forms of the same gene with small differences in their sequence of DNA bases. These small differences contribute to each person’s unique physical features. Scientists keep track of genes by giving them unique names. Because gene names can be long, genes are also assigned symbols, which are short combinations of letters (and sometimes numbers) that represent an abbreviated version of the gene name. For example, a gene on chromosome 7 that has been associated with cystic fibrosis is called the cystic fibrosis transmembrane conductance regulator; its symbol is CFTR. 7.2: Structure of a GeneA gene is the fundamental unit of heredity. Every individual has two copies of each gene, one inherited from each parent. Although most people contain the same genes, there is a small fraction that is slightly different amongst people. A gene with a small difference in its sequence of DNA bases forms different alleles, contributing to different phenotypes. However, only 1% of the DNA is composed of genes that encode proteins; the rest, 99% is non-coding DNA. This non-coding DNA performs different functions within a cell but is mainly involved in gene regulation. They act as regulatory elements, providing a site for transcription factors or other regulatory proteins to bind and activate or repress the gene activity. Gene Regulation An average human cell genome contains approximately 30,000 to 120,000 genes, but only a fraction of them are expressed in any specific cell at one time. This is why despite containing the same set of DNA and genes, each cell type in a human body looks different and performs different functions. It is accomplished through gene regulation, i.e., expression of specific genes at proper time and location. Gene regulation can happen at the level of DNA or RNA. Cells have internal chemical mechanisms that control when a gene is expressed to make RNA and protein, how much of the protein is made, and when to stop making that protein because it is no longer needed. The cells thus turn on the genes only when required, helping them save space and energy. If the cells were to express all genes at once, not only would they require a significant amount of energy but also enormous size because DNA must be unwound from its tightly coiled structure to be transcribed and translated into protein. Prokaryotic and eukaryotic cells regulate gene expression at different levels. In prokaryotic organisms, the primary control of gene expression is mainly at the transcriptional level, which means that the RNA is continuously transcribed until a protein is required, and it stops when the protein is no longer needed. In contrast, in eukaryotic cells, the processes of transcription and translation are physically separated by the nuclear membrane, adding to the complexity. Transcription occurs only within the nucleus, and translation occurs only outside the nucleus in the cytoplasm. Here, the regulation of gene expression can occur at different stages of the process. It can be regulated when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetic level), when the RNA is transcribed (transcriptional level), when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level), when the RNA is translated into protein (translational level), or after the protein has been made (post-translational level). This text is partially adapted from Openstax, Biology 2e, Section 16.1: Regulation of Gene Expression. Genes are functional units of heredity as they are made of DNA. The chromosome is made of DNA containing many genes. Every gene comprises of the particular set of instructions for a particular function or protein-coding. Speaking in usual terms, genes are responsible for heredity.  There are about 30000 genes in each cell of the human body. DNA present in the gene comprises only 2 percent of the genome. Many studies have been made on the same that found the location of nearly 13000 genes on each of the chromosomes. William Bateson introduced the term genetics in the year 1905. Later, Wilhelm Johannes was the first one who coined the term GENE in 1909. He was a Danish botanist. He named it as Gene to symbolise hereditary. Also Read: Difference between gene and allele Characteristics determined by GenesThe human cell contains 23 pairs of chromosomes. The trait is one of the characteristics determined by one or more genes. Abnormal genes and genes that are formed due to new mutations also result in certain traits. Genes vary in size depending on the code or the protein they produce. All cells in the human body contain the same DNA. The difference between the cells occurs due to the different type of genes that are turned on and therefore produce a variety of proteins. Reasons for hereditaryGenes come in pairs in the same way as the chromosomes. Each parent of a human being carries two copies of their genes and each parent passes one copy of genes to their child. This is the reason why the child has many characteristics of both the parents like hair colour, same eyes etc. Functions of Genes
To know more about the Genes and its importance, visit BYJU’S. What is the structure of genes called?Structure of DNA
DNA (deoxyribonucleic acid) is the cell's genetic material, contained in chromosomes within the cell nucleus and mitochondria. Except for certain cells (for example, sperm and egg cells and red blood cells), the cell nucleus contains 23 pairs of chromosomes. A chromosome contains many genes.
What is the structure and function of A gene?Genes are made up of DNA. Some genes act as instructions to make molecules called proteins. However, many genes do not code for proteins. In humans, genes vary in size from a few hundred DNA bases to more than 2 million bases.
What is the structure of structural gene?Structural genes are those genes that code all the proteins in a genome except regulatory genes. Regulatory genes are those genes that code for proteins or factors that control the expression of structural genes. In prokaryotes, structural genes are present in a sequence called operon.
How is the structure of DNA usually described?A molecule of DNA consists of two strands that form a double helix structure. DNA is a macromolecule consisting of two strands that twist around a common axis in a shape called a double helix.
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