gladiatrix
Card-carrying EAC member
Wrong! Random mutations are the key to the creation of new alleles. All other methods merely rearrange the existing alleles in the gene pool. During meiosis this rearrangement of alleles is due to crossing-over between the arms of non-sister chromatids during tetrad formation of Prophase I of Meiosis I (there are two parts to meiosis).mark kennedy said:New alleles are produced as a result of meiosis and represent changes of the existing gene pool.
For a really good explanation of crossing-over:
DNA from the Beginning:Genes Get Shuffled when chromosomes exchange pieces (CLICK on the ANIMATION icon)
Shuffling genes usually doesn't result in an alteration to any of the genes involved in the crossing-over events. Errors can and do happen and it is the ERRORS that can result in mutations IF the sequence of the gene or genes involved is altered by the crossing-over. Swapping genes around results in genetic diversity, but that is not the same thing a creating new alleles. One may get a new phenotype as the result of a particular new combination of alleles, but the alleles themselves usually have not changed.
Animated Meiosis Tutorial
WHAT IS A MUTATION?
Mutations are any permanent, heritable alterations in DNA. These alterations can be simple as a single base change (most common), insertions/deletions/rearrangements of segments of varying lengths, or can involve large pieces of DNA (visible pieces of chromosomes or whole chromosomes)
Chromosomes Carry Genes
Mutations are changes in genetic information
Mutations (categories with examples)
MUTATIONS HAVE BEEN OBSERVED.....
1. First, there may be an observable change (one that you can actually see) in the phenotype of the individual. For instance, a seed from a plant whose progeny are tall (phenotype or physical manifestation of gene expression) now has some offspring that are short as well as tall.
2. Second, if one can isolate the gene responsible for height, it is possible to take the "height gene" from the tall plant and the one from the short plant and compare the sequence to find the change. How this kind of thing is done and it's history, explained in the following animation:
A gene is a discrete sequence of DNA nucleotides
This is an image of a sequence, showing the individual bases for a gene. (left) If there was a mutation, then one can compare the sequence of the mutant gene to that of the "wild type" gene to find the difference or differences between them. An example of a case where as single base change can result in a dramatic change is sickle-cell anemia.(right).


3. Some mutations involve large segments of DNA (pieces of chromosome, even whole chromosomes)...............
An example of such an extensive mutation is Down's syndrome. The most common reason for this is that the person is born with 3 copies of chromsome 21 instead of just 2 (normal). That is why Down's syndrome is also called Trisomy 21 (tri- means 3).
Here is a picture of the karyotype of a male Down's sufferer showing this:

4. Some types of cancer are the result of unfortunate rearrangements between chromosomes called translocations (2 chromosomes exchange parts). A classic case is Burkitt's lymphoma. Here is a karyotype of a cancer cell showing the translocation between chromosome 8 and chromosome 14 (click on the link for an explanation)

5. Many cancers are the result of many different kinds of mutations (point mutations, deletions, insertions, translocations). Read about that HERE (pdf).
WHAT WOULD CAUSE MUTATIONS?
A. Any number of things can damage DNA in such a way as to cause mutations. They are called mutagens. If the resulting mutations cause cancer, these mutagens are also regarded as carcinogens:
- Many mutations result from copying errors by the molecules that make new copies of the DNA (also mechanisms in place that prevents or repairs most of these)
- Mutations can be the outcome of spontaneous degradation of the DNA due to the fact that it resides in a salty, aqueous environment (conditions inside the cell itself) like the deamination of cytosine mentioned later in this message. Think of it as cellular "wear and tear" on the DNA (repair mechanisms in place that fix the vast majority of these)
- many chemicals
- UV (ultra-violet) light (why tanning is bad for you)
- X-ray
- ionizing radiation
- DNA Repair Proteins
- DNA repair in the bacterium E. coli (these mechanisms were first discovered in bacteria)
- DNA repair gene in humans
D. The fact that HIV mutates rapidly was used to convict a killer. Dr. Richard Schmidt was convicted of purposely injecting Janice Trayhan, a former lover, with blood tainted with HIV and hepatitis C after she called off their affair. The blood was believed to have been drawn from an HIV- and HCV-positive patient around the time of the breakup. The state's expert witnesses established that PCR-based analysis of human HIV can be used to identify HIV strains
Although the DNA sequences used to establish the source of the infections were not identical with the sequences in the infected individuals, HIV is known to mutate rapidly. Even within an infected individual, the virus changes over time. The biological or statistical question, therefore, is how the viral sequence variation in individuals infected from a common source compares to the extent of variation among individuals infected from disparate sources. For a full explanation click on the following link:
1. Guilty Sequence (or Evolution via Phylogenetic Analysis gets its day in court)
2. Gretchen Vogel, Phylogenetic Analysis: Getting Its Day in Court, 275 Science 1559 (1997) (NOTE: this case cited in 29+ Evidences for Macroevolution
3.Ancient Remnants of Viral Infection Demonstrate Evolution Beyond a Reasonable Doubt
A mutation a rare transcription error?? Wrong again!mark kennedy said:Now if a mutation could produce a new gene then it might be considered an allele but most often a mutation is nothing more then a rare transcription error.
Think of DNA as an instruction book. When you need information about something you make a copy of the pages (genes) you're interested in, returning the book to the library. This way you don't have to risk losing or destroying the book. Transcription is a cell's way of simply copying the gene (instruction) of interest into a DISPOSABLE RNA copy (known as a "messenger"-RNA or m-RNA). The cytoplasm is a dangerous environment for the DNA and the daily transcription of genes to proteins would be very harmful to the DNA, which has to stay intact in order to maintain life. Therefore, RNA works as a sort of throw-away version of DNA (like the copies from the reference book) - good for limited work but not for long-term storage.
Here's an overview(click on link for an outline of the process of transcription)

The fact is that mutations usually DO NOT occur during transcription. DNA can become damaged during transcription, but DNA damage is NOT the same thing as a mutation, rather it is a "pre-mutational event". For instance a cytosine (C) may be deaminated (an amino group removed and as a result, becomes a uracil (U). Uracil is not "tolerated" in DNA and is quickly repaired.
If the repair machinery doesn't remove the uracil (U, found in RNA instead of thymine, T), it will be "read" by the DNA polymerase of replication machinery as a "thymine (T)". The DNA polymerase will put an adenine (A) in the new daughter strand and THEN you would have a mutation. Remember that if the cytosine(C) were there, a guanine (G) would be put into the new strand by the DNA polymerase like it should be. What you would get if the uracil is not repaired is a G ==>A, a type of point mutation known as a transition mutation.
The effect the mutation has depends on whether the mutation occurs in a somatic cell or in a germline cell
Helpful sites that explain these mechanism:The significance of mutations is profoundly influenced by the distinction between germline and soma. Mutations that occur in a somatic cell, in the bone marrow or liver for example, may
* damage the cell
* make the cell cancerous
* kill the cell
Whatever the effect, the ultimate fate of that somatic mutation is to disappear when the cell in which it occurred, or its owner, dies.
Germline mutations, in contrast, will be found in every cell descended from the zygote to which that mutant gamete contributed. If an adult is successfully produced, every one of its cells will contain the mutation. Included among these will be the next generation of gametes, so if the owner is able to become a parent, that mutation will pass down to yet another generation
Types of Mutations
DNA Repair Mechanisms
DNA Replication
Well, finally a true statement, however, mutations are the result of transcription errors, either. The end results of a transcription error may be no product (protein, r-RNA or t-RNA), but more usually just a faulty protein, r-RNA or t-RNA.mark kennedy said:An allele is not a transcription error.
There are beneficial mutations, but do continue to bury your head in the sand and deny that they happen, despite repeated examples being shown to you on that subject. There is no need for a drastic change to occur in the gene pool for a radical alteration to occur in a phenotype.mark kennedy said:and a mutation is not an improvement of the existing gene pool
Mutations and Evolution
If your remarks above weren't so totally off the mark, I'd laugh at the profound irony of the hubris of the above remark. In other words,you certainly have NOT "diserned" one iota of the facts about genetics or how DNA, RNA function.mark kennedy said:I don't know what is so confusing about this since it's all readily disernable.
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