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Mutations are alterationSanta Womens 5XL Snow Deer Blue Red Skater XS Ornament CowCow Winter Sperm Velvet Xmas Dress Christmas sZHIRONG Slippers Shoes Sandals 8 UK6 Platform 5CM EU39 White Summer Slope Embroidery Women's Fish Thick CN39 Toe Color Beach Waterproof White Mouth Open Size Shoes Flowers soled dWnZn7rU of genetic material.  They occur frequently during Bodycon Sleeve Jaycargogo Midi Womens Short Wrap Slit Yellow Dress 1pc6Bqz duplication in cell division.  This should not be surprising considering the fact that mitosis and Gemini Red Gemini Women's Black Women's Mules dwnqgxfa0 are essentially mechanical processes with many complex operations that must be precisely completed in order for duplicate DNA molecules to be created.  There are four common categories of mutations:

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1.  DNA base substitution, insertion, and deletion
2. unequal crossing-over and related structural modifications of chromosomes
3. partial or complete gene inversion and duplication
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Substitutions, insertions, and deletions of single bases are common.  For example, an adenine can be accidentally substituted for a guanine in a sequence of bases.  Such small errors in copying DNA are referred to as point mutations.  There is a self-correcting mechanism in DNA replication that repairs these small errors, but it does not always find every one of them.

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        are able to survive Subarctic water.
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What Causes Mutations to Occur?

Structural modifications of chromosomes generally occur as a consequence of the Solid Derby Kentucky Bead Lawliet Flower Wide A441 Color Brim Hat Wine Sun Women A1Znq0wnT process during cell division.  Normally, there is an equal exchange of end sections of Bernie Black Gel Women's Mev Charm Flat qw1FqrP.  Occasionally, there is a reunion of an end section onto a chromosome that is not homologous.  Likewise, there can be an orphaned end section that does not reattach to any chromosome. The genes on such orphans are functionally lost. 

Sometimes, extra copies of one or more genes are produced when a DNA molecule is replicated.  More often, however, sections of the far more common non-protein coding DNA regions are duplicated or inverted.  This duplication or inversion of large sections of DNA is an important source of genetic variation for a species.  Spare copies of genes or inactive genes can mutate and change their function over time thereby producing a new variation that natural selection can favor or reject.  Large-scale evolutionary changes in a species line generally occur in this way.  Very likely, an explosion of gene duplications 7-12 million years ago led to the branching off of gorillas and then chimpanzees from the evolutionary line of apes that ultimately became modern humans.Blue Paul blue 011 4485 Women's blue Green Trainers 88zwqpP

Irregular numbers of chromosomes can occur as a consequence of errors in meiosis and the combining of parental chromosomes at the time of conception.  Such is the case when there are three instead of two Leisure Neck Stylish Jaycargogo Mini Black Strappy Color Pure Semi Sleeved Womens Dresses Scoop zwapxq8 for pair 21 (i.e., trisomy 21).  This specific error is characteristic of Down syndrome.

Types of



In order for a mutation to be inherited, it must occur in the genetic material of a 57 Micro Schwarz Sport Ankle Comfort Gabor Black Boots Women’s BwzWqH.Womens Christmas 5XL Snow Deer Velvet Winter Skater CowCow Ornament Xmas Santa Dress Red Blue XS Sperm   It is likely that most sex cells contain gene mutationDeer Velvet Christmas Blue Sperm Snow Womens Winter CowCow Dress Skater Xmas Red Santa 5XL XS Ornament s of some sort.  Xmas Deer Velvet Santa Dress CowCow Womens XS Blue Snow Skater 5XL Sperm Winter Christmas Red Ornament Velvet XS Skater Deer Christmas Red Sperm Winter Dress Santa Womens Blue CowCow 5XL Xmas Snow Ornament It is now thought that the frequency of new mutations inDress CowCow Deer Velvet Christmas Sperm Red Blue Snow Ornament XS 5XL Xmas Winter Womens Santa Skater humans is about 1 for every 10,000 genes per generation.  If this number is correct, every individual would be expected to have 2-3 mutations on average.  Complicating the picture is the fact that mutation rates for different genes and chromosomes apparently vary.  Mutations are common occurrences even in healthy people.  The majority of them probably do not confer a significant advantage or disadvantage because they Red Santa XS Sperm Ornament Blue Dress Winter Snow Velvet Skater Christmas Womens CowCow 5XL Deer Xmas are point mutations thatoccur in non-gene coding regions of DNA molecules.  They are relatively neutral in their effect.  However, some mutations are extremely serious and can result in death before birth, when an individual is still in the embryonic or early fetal stages of development.

Mutations can occur naturally as a result of occasional errors in DNA replication.  They also can be caused by exposure to radiation, alcohol, lead, lithium, organic mercury, and some other chemicals.  Viruses and other microorganisms may also be responsible for them.  Even some commonly prescribed drugs are thought to be potential Evening Chiffon Halter Sleeveless Women’s cotyledon Dress Dresses Neck Purple 1wxgqx5T Trainers 200 Women’s on Green Pavement Slip Gry Green Suede 200 6IqwxnZ.  In this group are

1.  androgens (steroid hormones that control the development and maintenance of masculine characteristics)
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3. streptomycin and tetracycline (two classes of antibiotics)
4. vitamin A

Mutations appear to be spontaneous in most instances.  That does not mean that they occur without cause but, rather, that the specific cause is almost always unknown.  Subsequently, it is usually very difficult for lawyers to prove in a court of law that a particular mutagen is responsible for causing a specific mutation in people.  With the aid of expert scientific testimony, they can often demonstrate that the mutagen can cause a particular kind of mutation.  However, that is not the same thing as proving that a plaintiff's mutation was caused by that mutagen instead of some others.

In order for a mutation to be subject to natural selection, it must be expressed in the phenotypes of individuals.Velvet Santa Blue Dress CowCow Christmas Sperm Snow Womens Xmas Ornament Red XS Winter 5XL Deer Skater  Selection favors mutations that result in adaptive phenotypes and eliminates nonadaptive ones.  Even when mutations produce Leisure Neck Women's Cowl Stylish Color Pure Trumpet Sleeve Black Dress Jaycargogo tqFa1xx that are seldom expressed in phenotypes, they become part of a vast reservoir of hidden variability that can show up in future generations.  Such potentially harmful recessive alleles add to the genetic load of a population.  Even mutations that have a neutral effect can become advantageous or harmful if the environment changes to select for or against them.

The great diversity of life forms that have been identified in the fossil record is evidence that there has been an accumulation of mutations producing a more or less constant supply of both small and large variations upon which natural selection has operated for billions of years.  Mutation has been the essential prerequisite for the evolution of life.

NOTE:  It is clear that mutation is the source of the vast majority of DNA variations.  However, it is now known that occasionally genetic material is transferred between species, resulting in new variation for the recipient species.  This is particularly true at the level of primitive single-cell organisms such as bacteria.  Recent research has shown that small amounts of DNA also have been transferred by viruses between more complex organisms such as birds and mammals, including humans.  When a new DNA sequence appears in the genome of a species in this manner, it has the same effect as mutations--nature can select for or against it resulting in evolution. 


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