What is a Gene?

A gene is a unit of heredity in a living organism. It normally resides on a stretch of DNA that codes for a type of protein or for an RNA chain that has a function in the organism. All living things depend on genes, as they specify all proteins and functional RNA chains.

Genes hold the information to build and maintain an organism’s cells and pass genetic traits to offspring, although some organelles (e.g. mitochondria) are self-replicating and are not coded for by the organism’s DNA.

The notion of a gene is evolving with the science of genetics, which began when Gregor Mendel noticed that biological variations are inherited from parent organisms as specific, discrete traits.

The biological entity responsible for defining traits was later termed a ”gene”, but the biological basis for inheritance remained unknown until DNA was identified as the genetic material in the 1940s.

All organisms have many genes corresponding to many different biological traits, some of which are immediately visible, such as eye color or number of limbs, and some of which are not, such as blood type or increased risk for specific diseases, or the thousands of basic biochemical processes that comprise life.

The vast majority of living organisms encode their genes in long strands of DNA. DNA (deoxyribonucleic acid) consists of a chain made from four types of nucleotide subunits, each composed of: a five-carbon sugar (2′-deoxyribose), a phosphate group, and one of the four bases adenine, cytosine, guanine, and thymine.
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What is Human Genetics?

Human genetics is defined as the study of how genetic inheritance takes place in the human species, or how inheritance of various characteristics from parents to kids takes place. The process of genetic inheritance in human beings and the study of human heredity now hold a central position in the field of science. The interest in the query “What is Human Genetics” is fueled from the fundamental need to understand how human genetics and the process of human inheritance affect the manifestation of genetic disorders.
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What is Genetics

Genetics is the study of heredity, the process in which a parent passes certain genes onto their children. A person's appearance -- height, hair color, skin color, and eye color -- are determined by genes. Other characteristics affected by heredity.

alternative name of genetics is Homozygous, Inheritance, Heterozygous, Inheritance patterns, Heredity and disease, Heritable, Genetic markers.

Human beings have cells with 46 chromosomes -- 2 sex chromosomes and 22 pairs of nonsex (autosomal) chromosomes. Males are "46, XY" and females are "46, XX." The chromosomes are made up of strands of genetic information called DNA.

Genes are sections of DNA. The location of the gene is called the locus. Most genes carry information that is necessary to make a protein.

The pairs of autosomal chromosomes (one from the mother and one from the father) carry basically the same information. That is, each has the same genes. However, there may be slight variations of these genes. These slight differences occur in less than 1% of the DNA sequence and produce variants of a particular gene called alleles.

If a gene is abnormal, it may lead to an abnormal protein or an abnormal amount of a normal protein. Since the autosomal chromosomes are paired, there are two copies of each gene, one from each parent. If one of these genes is defective, the other may make enough protein so that no disease is seen. This is called a recessive disease, and the gene is said to be inherited in a recessive pattern.

However, if only one abnormal gene is needed to produce a disease, it's called a dominant hereditary disorder. In the case of a dominant disorder, if one abnormal gene is inherited from mom or dad, the child will likely show the disease.

A person with one abnormal gene is termed heterozygous for that gene. If a child receives an abnormal recessive disease gene from both parents, the child will show the disease and will be homozygous for that gene.

If two parents each have one copy of a recessive disease gene, then each child has a 25% (1 in 4) chance of showing the disease. If one parent has two copies of the disease gene and the other has one copy, then each child has a 50% (1 in 2) chance of being homozygous.

Resource : www.righthealth.com
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Genetics Definition

Genetics is the study of heredity, the process in which a parent passes certain genes onto their children. A person's appearance -- height, hair color, skin color, and eye color -- are determined by genes. Other characteristics affected by heredity:

- Likelihood of getting certain diseases
- Mental abilities
- Natural talents

An abnormal trait (anomaly) passed down through families (inherited) may:

- Have no effect on your health or well being -- for example, it may just involve a white patch of hair or an extended earlobe
- Be of minor consequence -- for example, color blindness
- Have a dramatic effect on your quality or length of life

For most genetic disorders, genetic counseling is advised. Many people may also want to seek prenatal diagnosis.

The terms anomaly, abnormality, disorder, defect, disease, and syndrome are not used consistently, and do not have precise definitions.
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What is RNA?

RNA is transcribed from DNA by enzymes called RNA polymerases and is generally further processed by other enzymes. RNA is central to protein synthesis. Here, a type of RNA called messenger RNA carries information from DNA to structures called ribosomes. These ribosomes are made from proteins and ribosomal RNAs, which come together to form a molecular machine that can read messenger RNAs and translate the information they carry into proteins. There are many RNAs with other roles – in particular regulating which genes are expressed, but also as the genomes of most viruses. 

RNA and DNA are both nucleic acids, but differ in three main ways. First, unlike DNA which is double-stranded, RNA is a single-stranded molecule in most of its biological roles and has a much shorter chain of nucleotides. Second, while DNA contains ”deoxyribose”, RNA contains ”ribose” (there is no hydroxyl group attached to the pentose ring in the 2′ position in DNA). These hydroxyl groups make RNA less stable than DNA because it is more prone to hydrolysis. Third, the complementary base to adenine is not thymine, as it is in DNA, but rather uracil, which is an unmethylated form of thymine. For instance, determination of the structure of the ribosome—an enzyme that catalyzes peptide bond formation—revealed that its active site is composed entirely of RNA.
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