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Contact a health care provider if you have questions about your health. How are gene variants involved in evolution? From Genetics Home Reference. Topics in the Variants and Health chapter What is a gene variant and how do variants occur? How can gene variants affect health and development?
Do all gene variants affect health and development? What kinds of gene variants are possible? Can a change in the number of genes affect health and development? Can changes in the number of chromosomes affect health and development? Can changes in the structure of chromosomes affect health and development? These occur in reproductive cells like eggs and sperm and are called germ line mutations. This can happen in many situations: perhaps the mutation occurs in a stretch of DNA with no function, or perhaps the mutation occurs in a protein-coding region, but does not affect the amino acid sequence of the protein.
For example, in humans, Marfan syndrome is caused by a mutation affecting a protein that forms part of connective tissue, leading to heart problems and other health challenges. Detrimental mutations known as lethals disrupt DNA critical to survival and cause the death of the organism. Beneficial effect Other mutations are helpful to the organisms that carry them.
For example, DDT resistance in insects is sometimes caused by a single mutation. While resistant insects might be downer for us, they are undoubtedly helpful for bugs trying to survive on pesticide-laden crops.
According to popular culture, it seems that mutations mainly cause either cancer or superpowers. Of course, the cancer is true enough.
But in the real world, beneficial mutations are rare. Most mutations have no effect or a detrimental effect. Point substitutions are in red, and the yellow box with dashes indicates a deletion of 12 bases. Mutations can have a range of effects. They can often be harmful. Others have little or no detrimental effect. And sometimes, although very rarely, the change in DNA sequence may even turn out to be beneficial to the organism.
A mutation that occurs in body cells that are not passed along to subsequent generations is a somatic mutation. A mutation that occurs in a gamete or in a cell that gives rise to gametes are special because they impact the next generation and may not affect the adult at all.
Such changes are called germ-line mutations because they occur in a cell used in reproduction germ cell , giving the change a chance to become more numerous over time. If the mutation has a deleterious affect on the phenotype of the offspring, the mutation is referred to as a genetic disorder.
Alternately, if the mutation has a positive affect on the fitness of the offspring, it is called an adaptation. Thus, all mutations that affect the fitness of future generations are agents of evolution. Mutations are essential to evolution. Every genetic feature in every organism was, initially, the result of a mutation.
The new genetic variant allele spreads via reproduction, and differential reproduction is a defining aspect of evolution. It is easy to understand how a mutation that allows an organism to feed, grow or reproduce more effectively could cause the mutant allele to become more abundant over time. Even deleterious mutations can cause evolutionary change, especially in small populations, by removing individuals that might be carrying adaptive alleles at other genes.
Hyla versicolor , is an example of mutation and its potential effects. When an ancestral Hyla chrysocelis gray treefrog failed to sort its 24 chromosomes during meiosis, the result was H.
This treefrog is identical in size, shape and color to H. All rights reserved. Most mutations occur at single points in a gene, changing perhaps a single protein, and thus could appear unimportant. For instance, genes control the structure and effectiveness of digestive enzymes in your and all other vertebrate salivary glands.
At first glance, mutations to salivary enzymes might appear to have little potential for impacting survival. Yet it is precisely the accumulation of slight mutations to saliva that is responsible for snake venom and therefore much of snake evolution. Natural selection in some ancestral snakes has favored enzymes with increasingly more aggressive properties, but the mutations themselves have been random, creating different venoms in different groups of snakes.
Snake venoms are actually a cocktail of different proteins with different effects, so genetically related species have a different mixture from other venomous snake families. The ancestors of sea snakes, coral snakes, and cobras family Elapidae evolved venom that attacks the nervous system while the venom of vipers family Viperidae; including rattlesnakes and the bushmaster acts upon the cardiovascular system.
Both families have many different species that inherited a slight advantage in venom power from their ancestors, and as mutations accumulate the diversity of venoms and diversity of species increased over time. Although the history of many species have been affected by the gradual accumulation of tiny point mutations, sometimes evolution works much more quickly. Several types of organisms have an ancestor that failed to undergo meiosis correctly prior to sexual reproduction, resulting in a total duplication of every chromosome pair.
Such a process created an "instant speciation" event in the gray treefrog of North America Figure 2. The consequence of doubling the genome size in plants is often abnormally large seeds or fruits, a trait that can be of distinct advantage if you are a flowering plant! Most cereals that humans eat have enormous seeds compared to other grasses, and this is often due to the genomic duplications that occurred in the ancestors of modern rice and wheat and, because the mistake occurred in reproductive organs, was successfully passed on to future generations.
Humans themselves have mimicked this process by interbreeding individual plants with the largest fruits and seeds in the process of artificial selection, creating many of our modern agricultural crop strains.
The idea of evolution by natural selection, first described by Charles Darwin and Alfred Russell Wallace, requires differential survival due to some individuals having greater evolutionary fitness.
Whether that fitness is affected by genetic disorders, venomous saliva or enlarged offspring, heritable variation can only arise by mutation. Evolution is simply not possible without random genetic change for its raw material.
Allendorf, F. Conservation and the Genetics of Populations. Malden, MA: Blackwell Publications,
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