Table of ContentsView AllTable of ContentsGenesDNAChromosomesVariationsGenetic TestingGenetic Disorders
Table of ContentsView All
View All
Table of Contents
Genes
DNA
Chromosomes
Variations
Genetic Testing
Genetic Disorders
Genes are the basic units that determine the traits that we inherit from our parents.They contain coded information found in nearly every cell of the human body.
Our genes are made up of DNA, a molecule with this coded information. Hundreds to thousands of genes are found on each chromosome inside our cells.Together, the DNA, genes, and chromosomes make up the complete set of genetic instructions for every individual—referred to as a genome. These instructions include a person’s sex, features, and risk of medical conditions.
The Human Genome Project, founded in 1990, mapped the entire human genome to understand how genes and chromosomes influence diseases and to find better ways to treat them. Based on information from the project, scientists have been able to discover over 1,800 genes that cause disease and, in turn, create tests and medicines to help diagnose and treat them.
Andrew Brookes / Getty Images
What Are Genes Made Of?
Genes are composed of DNA and encoded for a specific purpose. How genes are encoded will determine how you look or how your body functions. Every person has two copies of a gene, each inherited from a parent.
Some genes provide instructions to produce specific types of proteins. Proteins are the molecules that not only make up tissues (like muscles and skin) but also play critical roles in the development and function of the body.
Other genes are encoded to produce RNA (ribonucleic acid), a molecule that converts the information stored in DNA to make protein.Different versions of a gene are known asalleles.
Every human has around 20,000 genes, half inherited from a person’s mother and half inherited from a person’s father.
The alleles you inherit from your parents may determine, for example, if you have brown eyes or blue eyes. Others may lead to congenital (inherited) disorders likecystic fibrosisorHuntington’s disease. Others still may not cause disease but may increase your risk of getting one (likecancer).Genes only make up between 1% and 5% of the human genome. The rest is made up of non-coded DNA that doesn’t produce protein but helps regulate how genes function.
What Is DNA Made Of?
DNA (deoxyribonucleic acid) is a building block that makes up your genes.
The bases pair up with each other—A with T and C with G—to form units known as base pairs. The pairs are then attached to form what looks like a spiraling ladder, known as adouble helix.
The specific order, or sequence, of these nucleotide bases determines which instructions are given.
Human DNA consists of around 3 billion of these bases, of which 99% are the same for all humans. The remaining 1% is what differentiates one human from the next.
How Genetic Disorders Are Inherited
What Are Chromosomes Made Of?
Chromosomes are made up of around 1,000 genes. In total, there are two sets of 23 chromosomes in nearly every cell of the body, one set inherited from a person’s mother and the other from a person’s father.
One pair of chromosomes, called thesex chromosomes, determines whether you are born male or female. Females have a pair of XX chromosomes, while males have a pair of XY chromosomes.
The other 22 pairs are calledautosomal chromosomes. These determine the rest of your body’s makeup.
Certain genes within these chromosomes may either be dominant or recessive. This can determine which traits predominate and which don’t. By definition:
What Is a Genome?Agenomeis the complete set of genetic instructions that determine the traits and characteristics of an organism. It contains all the information needed for an individual to develop and function, based on their chromosomes, genes, and DNA.While the genome of each species is distinct, every organism within that species has its own unique genome. This is why no two people are exactly alike, including twins.
What Is a Genome?
Agenomeis the complete set of genetic instructions that determine the traits and characteristics of an organism. It contains all the information needed for an individual to develop and function, based on their chromosomes, genes, and DNA.While the genome of each species is distinct, every organism within that species has its own unique genome. This is why no two people are exactly alike, including twins.
Agenomeis the complete set of genetic instructions that determine the traits and characteristics of an organism. It contains all the information needed for an individual to develop and function, based on their chromosomes, genes, and DNA.
While the genome of each species is distinct, every organism within that species has its own unique genome. This is why no two people are exactly alike, including twins.
What Is Genetic Variation?
Genes are prone to coding errors. Many errors won’t make any significant difference in the structure or function of a person’s body, but some can.
Some genetic variations will directly cause a defect or disease, some of which may becongenital(seen at birth) and others that may only be seen later in life.
Other variations can lead to changes in the entire “gene pool” (the characteristic genes in a population) that will affect inheritance patterns in later generations.
There are three common types of genetic variation:
Genetic Mutations
Genetic Recombination
Genetic recombination is a process in which pieces of DNA are broken, recombined, and repaired to produce a new allele. Also referred to as “genetic reshuffling,” recombination occurs randomly in nature during a normal event during cell division. The new allele can then be passed from parents to offspring.
Down syndrome is one such example of genetic recombination.
Genetic Migration
Genetic migration is an evolutionary process in which the addition or loss of people in a population changes the gene pool, making certain traits either less common or more common.
A theoretical example is the loss of red-haired people from Scotland, which over time may result in fewer and fewer Scottish children being born with red hair.
Based on the findings of the Human Genome Project, scientists have been able to create over 2,000genetic teststo help diagnosegenetic disordersor predict your risk of getting them. Genetic testing can be performed on blood, skin, hair,amniotic fluid, or other body tissues.
Genetic tests look for specific DNA mutations associated with different diseases. If you are suspected of having an inheritable disease or have a family history of one, genetic testing may be recommended.
Other reasons for testing include:
Some of these tests have a higher prognostic (predictive) value than others. While some test results are conclusive, delivering a positive or negative result, others may require agenetic counselorto help you understand what a result does and doesn’t mean.
Today, there are not only lab-based tests to detect certain diseases but also home kits you can purchase at stores or online to help predict your risk. While the prognostic values of self-tests are improving, they are prone to inaccuracies.
Even so, a positive result may encourage you to see a healthcare provider for further testing (such as finding you have aBRCA mutationlinked to an increased risk ofbreast cancer).
Lab-based genetic testing can help detect an ever-increase range of disorders and diseases, including:
Summary
DNA is the building blocks that contain the coded instructions for building and maintaining a body. Genes are comprised of DNA and are tasked with making specific proteins that play a critical role in the structure and function of the body. Chromosomes containing thousands of genes are passed from parents to offspring and determine an individual’s unique traits.
Together, DNA, genes, and chromosomes make up each organism’s genome.
Genetic tests can detect mutations that may help diagnose or predict your risk of certain diseases. They can also be used to see if you or your partner are carriers of a gene you can pass to a child if you decide to get pregnant.
16 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.What is a gene?Merck Manual.Genes and chromosomes.Genomics England.What is a genome?National Human Genome Research Institute.The human genome project.MedlinePlus.What is DNA?MedlinePlus.What is a chromosome?Genetic Alliance.Appendix B. Classic Mendelian genetics (patterns of inheritance). In:Understanding Genetics: A District of Columbia Guide for Patients and Health Professionals.Washington, DC: District of Columbia Department of Health.National Human Genome Institute.Mutation.Shah DJ, Sachs RK, Wilson DJ.Radiation-induced cancer: a modern view.Br J Radiol.2014 Dec;85(1020):e1166–e1173. doi:10.1259/bjr/25026140Stapley J, Feulner PGD. Johnston SE, Santure AW, Smadja CM.Recombination: the good, the bad and the variable.Philos Trans R Soc Lond B Biol Sci. 2017 Dec 19;372(1736):20170279. doi:10.1098/rstb.2017.0279Ellstrand NC, Rieseberg LH.When gene flow really matters: gene flow in applied evolutionary biology.Evol Appl. 2016 Aug;9(7):833–6. doi:10.1111/eva.12402U.S. National Library of Medicine.What are the risks and limitations of genetic testing?National Society of Genetic Counselors.About genetic counselors.Oh B.Direct-to-consumer genetic testing: advantages and pitfalls.Genomics Inform.2019 Sep;17(3):e33. doi:10.5808/GI.2019.17.3.e33Ibrahim M, Yadav S, Ogunleye F, Zakalik D.Male BRCA mutation carriers: clinical characteristics and cancer spectrum.BMC Cancer. 2018;18(1):179. doi:10.1186/s12885-018-4098-yNational Library of Medicine.GTR (genetic testing registry).
16 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.MedlinePlus.What is a gene?Merck Manual.Genes and chromosomes.Genomics England.What is a genome?National Human Genome Research Institute.The human genome project.MedlinePlus.What is DNA?MedlinePlus.What is a chromosome?Genetic Alliance.Appendix B. Classic Mendelian genetics (patterns of inheritance). In:Understanding Genetics: A District of Columbia Guide for Patients and Health Professionals.Washington, DC: District of Columbia Department of Health.National Human Genome Institute.Mutation.Shah DJ, Sachs RK, Wilson DJ.Radiation-induced cancer: a modern view.Br J Radiol.2014 Dec;85(1020):e1166–e1173. doi:10.1259/bjr/25026140Stapley J, Feulner PGD. Johnston SE, Santure AW, Smadja CM.Recombination: the good, the bad and the variable.Philos Trans R Soc Lond B Biol Sci. 2017 Dec 19;372(1736):20170279. doi:10.1098/rstb.2017.0279Ellstrand NC, Rieseberg LH.When gene flow really matters: gene flow in applied evolutionary biology.Evol Appl. 2016 Aug;9(7):833–6. doi:10.1111/eva.12402U.S. National Library of Medicine.What are the risks and limitations of genetic testing?National Society of Genetic Counselors.About genetic counselors.Oh B.Direct-to-consumer genetic testing: advantages and pitfalls.Genomics Inform.2019 Sep;17(3):e33. doi:10.5808/GI.2019.17.3.e33Ibrahim M, Yadav S, Ogunleye F, Zakalik D.Male BRCA mutation carriers: clinical characteristics and cancer spectrum.BMC Cancer. 2018;18(1):179. doi:10.1186/s12885-018-4098-yNational Library of Medicine.GTR (genetic testing registry).
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
MedlinePlus.What is a gene?Merck Manual.Genes and chromosomes.Genomics England.What is a genome?National Human Genome Research Institute.The human genome project.MedlinePlus.What is DNA?MedlinePlus.What is a chromosome?Genetic Alliance.Appendix B. Classic Mendelian genetics (patterns of inheritance). In:Understanding Genetics: A District of Columbia Guide for Patients and Health Professionals.Washington, DC: District of Columbia Department of Health.National Human Genome Institute.Mutation.Shah DJ, Sachs RK, Wilson DJ.Radiation-induced cancer: a modern view.Br J Radiol.2014 Dec;85(1020):e1166–e1173. doi:10.1259/bjr/25026140Stapley J, Feulner PGD. Johnston SE, Santure AW, Smadja CM.Recombination: the good, the bad and the variable.Philos Trans R Soc Lond B Biol Sci. 2017 Dec 19;372(1736):20170279. doi:10.1098/rstb.2017.0279Ellstrand NC, Rieseberg LH.When gene flow really matters: gene flow in applied evolutionary biology.Evol Appl. 2016 Aug;9(7):833–6. doi:10.1111/eva.12402U.S. National Library of Medicine.What are the risks and limitations of genetic testing?National Society of Genetic Counselors.About genetic counselors.Oh B.Direct-to-consumer genetic testing: advantages and pitfalls.Genomics Inform.2019 Sep;17(3):e33. doi:10.5808/GI.2019.17.3.e33Ibrahim M, Yadav S, Ogunleye F, Zakalik D.Male BRCA mutation carriers: clinical characteristics and cancer spectrum.BMC Cancer. 2018;18(1):179. doi:10.1186/s12885-018-4098-yNational Library of Medicine.GTR (genetic testing registry).
MedlinePlus.What is a gene?
Merck Manual.Genes and chromosomes.
Genomics England.What is a genome?
National Human Genome Research Institute.The human genome project.
MedlinePlus.What is DNA?
MedlinePlus.What is a chromosome?
Genetic Alliance.Appendix B. Classic Mendelian genetics (patterns of inheritance). In:Understanding Genetics: A District of Columbia Guide for Patients and Health Professionals.Washington, DC: District of Columbia Department of Health.
National Human Genome Institute.Mutation.
Shah DJ, Sachs RK, Wilson DJ.Radiation-induced cancer: a modern view.Br J Radiol.2014 Dec;85(1020):e1166–e1173. doi:10.1259/bjr/25026140
Stapley J, Feulner PGD. Johnston SE, Santure AW, Smadja CM.Recombination: the good, the bad and the variable.Philos Trans R Soc Lond B Biol Sci. 2017 Dec 19;372(1736):20170279. doi:10.1098/rstb.2017.0279
Ellstrand NC, Rieseberg LH.When gene flow really matters: gene flow in applied evolutionary biology.Evol Appl. 2016 Aug;9(7):833–6. doi:10.1111/eva.12402
U.S. National Library of Medicine.What are the risks and limitations of genetic testing?
National Society of Genetic Counselors.About genetic counselors.
Oh B.Direct-to-consumer genetic testing: advantages and pitfalls.Genomics Inform.2019 Sep;17(3):e33. doi:10.5808/GI.2019.17.3.e33
Ibrahim M, Yadav S, Ogunleye F, Zakalik D.Male BRCA mutation carriers: clinical characteristics and cancer spectrum.BMC Cancer. 2018;18(1):179. doi:10.1186/s12885-018-4098-y
National Library of Medicine.GTR (genetic testing registry).
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