Gene
Genes are fundamental chemical structures located within the cells of all living organisms, serving as blueprints that guide the creation and functioning of new cells. They are inherited from parents, which is why certain traits, like eye color and hair type, often appear within families. The expression of these traits depends on whether the genes are dominant or recessive, with dominant genes typically prevailing. The study of genetics began with Gregor Mendel in the 19th century, who established foundational theories through his experiments with pea plants, leading to the identification of dominant and recessive traits.
Over the years, significant advancements in genetics have occurred, including the discovery of chromosomes and the mapping of the human genome, completed in 2003. Genes, composed of DNA, dictate specific actions that result in observable traits and are organized into chromosomes within the cell nucleus. Mutations can occur during DNA replication, sometimes leading to beneficial changes, but often resulting in inherited disorders such as cystic fibrosis and sickle cell anemia. Genetic counseling is an important resource for individuals and families who wish to understand the impacts of genetic inheritance on health.
On this Page
Subject Terms
Gene
Genes are chemical structures found in the cells of all living things. They act as a blueprint for the body, telling it how and where to create new cells. Genes are inherited from parents. This is why certain traits, such as eye color, nose shape, and hair color, tend to run in families.
In many cases, children will inherit a trait from both their mother and their father. Which trait is expressed depends on whether the gene is dominant or recessive. Dominant genes are typically expressed over recessive genes. If a single trait appears in a large number of family members, it is likely that the gene for that trait is dominant.
Background
Genetics, the study of genes, was pioneered in the mid- to late-nineteenth century by Gregor Mendel, who was a monk and scientific researcher. After studying at the University of Vienna, Mendel developed new theories about the nature of genetics. He performed experiments on thousands of pea plants, strictly controlling their breeding. In doing so, he was able to track exactly how they passed physical traits from one generation to the next.
Mendel noticed that certain physical traits were rarer than others. He also noticed that when he bred a pea plant expressing a common trait with a pea plant expressing a rare trait, the common trait was usually expressed in the offspring. Using this information, Mendel theorized that there were two types of genes: dominant and recessive. If an organism has both a dominant and a recessive gene, the dominant gene will be expressed. A recessive gene will only be expressed if the organism failed to inherit a dominant gene. Mendel's experiments supported his theories, and he published them in 1866.
Mendel's work was never taken seriously during his lifetime. However, when his journals and notes were discovered in 1900 by scientists Hugo de Vries, Carl Correns, and Erich von Tschermak, his theories proved revolutionary. The notes helped a large number of scientists with similar theories to build upon them. Soon it was discovered that structures called chromosomes existed inside a cell and a material called nucleic acid existed inside of them. Scientists later realized that this nucleic acid contained all the inheritable traits in an organism. These traits were first named genes by William Bateson in 1905.
A string of major breakthroughs in genetics followed. In 1910, geneticist Thomas Hunt Morgan proved that chromosomes could be mapped and genes reliably resided in specific places on chromosomes. Soon afterwards, scientists managed to map out the chromosome of the fruit fly. In 1941, scientists realized that mutations and abnormalities in an individual's chromosomes could cause the body's cells to act irregularly. This would later be revealed to be the cause of many inherited disorders.
The next major breakthrough in genetics occurred in 1972. Scientists at the University of Ghent realized that a single gene could be linked to multiple bodily proteins, which meant that a gene could control multiple traits. Armed with this information, they set out to map the human genome. To do so, scientists would have to understand the placement of every gene in the human chromosome. The Human Genome Project, an international effort to achieve this goal, published a completed map of the human genome in April 2003.
Genes, Genetics, and Heritage
Deoxyribonucleic acid (DNA) is a complex molecule and blueprint for a living organism. It is composed of two long strands of proteins intertwined to form a shape called a double helix. A gene is a segment of DNA that tells the body how to perform a specific action, resulting in an expressed trait. In modern genetics, these traits are called alleles.
Genes are passed down from parent organism to child organism. In sexually reproducing organisms, a child receives one copy of each gene from each parent. Which variant is expressed depends on the dominant or recessive status of the genes.
Genes are found in chromosomes, which are long X-shaped strands of proteins. Chromosomes are found in the nuclei of cells. When cells divide, chromosomes divide with them, creating a new, identical set of DNA for the new cell. This process is called mitosis and is undergone by all bodily cells.
Each cell contains two sets of chromosomes, and each human chromosome contains 46 individual chromosomes. Exactly 23 of these come from the father's sperm, and 23 come from the mother's egg. One set of chromosomes decides the sex of the individual, and the others contain numerous genes.
Chromosomes function like blueprints for a cell. While each cell contains a full set of DNA, a full body blueprint, many cells develop differently. For example, the cells in the lungs develop very differently from skin cells. The body initiates these different functions by activating or deactivating genes within a cell. Once they are formed, the activated genes within a cell tell it how to function.
Occasionally, genes undergo a process called mutation during which a gene is incorrectly copied from the parent, resulting in a new, different gene in the child. In some cases, mutations can result in a beneficial allele. However, many of the most commonly discussed mutations cause the body to abnormally or incorrectly form some of its proteins. These cause a variety of disorders, including cystic fibrosis, Tay-Sachs disease, Huntington's disease, color blindness, and sickle cell anemia. Many of these mutations can be passed from parent to child, causing the child to inherit the disease. Researchers have identified many mutations related to health issues such as breast cancer. Genetic counselors often work with patients to discuss risks and proactive measures to detect or avoid such medical developments.
Bibliography
KidsHealth.org. "What Is a Gene?" KidsHealth.org, The Nemours Foundation, 2016, kidshealth.org/en/kids/what-is-gene.html. Accessed 21 Oct. 2016.
Mandal, Amanda. "Gene History." News-Medical, AZO Network, 14 Oct. 2012, news-medical.net/life-sciences/Gene-History.aspx. Accessed 21 Oct. 2016.
Mandal, Amanda. "What Are Genes?" News-Medical, AZO Network, 14 Oct. 2012, w.news-medical.net/life-sciences/What-are-Genes.aspx Accessed 21 Oct. 2016.
MedlinePlus. "Why Might Someone Have a Genetic Consultation?" National Library of Medicine, 12 May 2021, medlineplus.gov/genetics/understanding/consult/reasons/. Accessed 14 Nov. 2024.
National Human Genome Research Institute. "Overview of the Human Genome Project." National Human Genome Research Institute, 24 Aug. 2022, www.genome.gov/about-genomics/educational-resources/fact-sheets/human-genome-project. Accessed 18 Jan. 2023.
"Stanford Explainer: CRISPR, Gene Editing, and Beyond." Stanford Report, 10 June 2024, news.stanford.edu/stories/2024/06/stanford-explainer-crispr-gene-editing-and-beyond. Accessed 14 Nov. 2024.
The Tech. "Mutations and Disease." The Tech, Stanford School of Medicine, 2013, genetics.thetech.org/about-genetics/mutations-and-disease. Accessed 21 Oct. 2016.
University of Arizona. "The Cell Cycle & Mitosis Tutorial." University of Arizona, University of Arizona, Oct. 2004, biology.arizona.edu/cell‗bio/tutorials/cell‗cycle/cells3.html. Accessed 21 Oct. 2016.