Several such variants are responsible for differences between people such as eye color, hair color, and blood type. Other chapters in Help Me Understand Genetics. Genetics Home Reference has merged with MedlinePlus. Learn more. The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health. What is a gene variant and how do variants occur? From Genetics Home Reference.
When an egg and a sperm cell unite, the resulting fertilized egg cell contains DNA from both parents. Any variants that are present in that DNA will be present in the cells of the child that grows from the fertilized egg. Because non-inherited variants typically occur in somatic cells cells other than sperm and egg cells , they are often referred to as somatic variants. These variants cannot be passed to the next generation.
Non-inherited variants can be caused by environmental factors such as ultraviolet radiation from the sun or can occur if an error is made as DNA copies itself during cell division. Topics in the Variants and Health chapter What is a gene variant and how do variants occur?
DNA is the recipe for all life on Earth, by coding for proteins that the entire organism is made of. Our bodies have complex systems in place that make sure our DNA is organized properly and that each new cell gets a complete and unchanged copy. If the complex system involved in copying DNA fails, or if bad things are present in the environment, a mistake in the sequence of DNA can occur.
Some mutations cause serious health problems. The purpose of this article is to highlight the many harmful villains, called mutagens that cause mutations, and how we can protect our bodies from harm by maintaining a healthy lifestyle and avoiding unnecessary exposure to the types of hazards that can cause mutations. Without DNA , you would literally not exist! Neither would your pet, the trees in your yard, nor the meat, fruits, and vegetables you had for lunch.
Anything that is or was alive can thank DNA! DNA is essentially a recipe that allows an organism to produce the basic materials proteins that make up each cell. Cells work together as tissues, organs, and organ systems to form an entire organism.
These four bases are strung together into a long chain. The order of the bases is referred to as the DNA sequence. Each set of three bases in the DNA sequence is referred to as a codon.
Most codons code for one of the 20 amino acids that make up proteins. When the codon does not correspond to an amino acid, it is referred to as a stop codon, because it tells the cell that the end of the recipe has been reached and that production of the protein is done. DNA normally exists as two strands that wind into a shape called a double helix, with the bases on the two strands paired in a predictable way: A always pairs with T, and G with C see Figure 1. To further enhance your understanding of the structure of DNA, we recommend the sweet pun intended depiction of the double helix made out of gummy bears and licorice, in the Frontiers for Young Minds article about the genetics of heart disease by Clark, Alibhai, and Rutland [ 1 ]!
So, how many of these bases are there? The ways you are different from your classmates, friends, and siblings is due to your DNA sequences being different from theirs. About half of your DNA comes from each of your parents. Now that we understand some basics about DNA, we can talk about how the sequence can change.
Sometimes our DNA sequence gets altered; this is called a mutation. There are different types of mutations. For example, a base can be changed from what it was originally supposed to be to a different base substitution , a base or bases can be deleted from the DNA deletion , a base or bases can be added to the DNA insertion , or a piece of DNA can be flipped inversion or repeated duplication see Figure 2. While mutations always change the DNA sequence, they do not always cause a change in the resulting protein or an obvious effect on the organism.
This can occur because most amino acids can be coded by two or more different codons. Mutations that do not affect the protein are called silent mutations, because the DNA still makes the same protein that would be expected, and a person with a silent mutation would not even realize it. Other times, the change in the DNA sequence does affect the protein. In this case, the amino acid glutamic acid would be replaced with valine.
This specific sequence change is the mutation found in most people with sickle cell anemia, which is a very painful condition. Other times, a base is inserted into or deleted in the DNA sequence, which alters the way codons are read. This results in a large number of amino acids being altered, which is called a frameshift mutation. Notice how none of the amino acids in the protein made from the mutated DNA are the same as the original sequence.
Sometimes, gene variants also known as mutations prevent one or more proteins from working properly. When a variant alters a protein that plays a critical role in the body, it can disrupt normal development or cause a health condition. A condition caused by variants in one or more genes is called a genetic disorder.
In some cases, gene variants are so severe that they prevent an embryo from surviving until birth. These changes occur in genes that are essential for development, and often disrupt the development of an embryo in its earliest stages.
Because these variants have very serious effects, they are incompatible with life. All people, including those without cystic fibrosis, have a version of the CFTR gene. Other chapters in Help Me Understand Genetics. Genetics Home Reference has merged with MedlinePlus.
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