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causes of mutations in DNA? watch

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    hello could someone please tell me 2 possible causes of mutation in DNA and chromosomes. thank you!
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    Are you looking for factors which increase the chance of a mutation occuring?
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    errr yes
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    1. Viruses. Some viruses can change the base sequence in DNA causing genetic disease and cancer.

    2. Chemicals that react with the DNA bases such as benzene, nitrous acid and tar in cigarette smoke.
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    thank you!
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    Gamma Rays!!!!!!!!!!!!!!!!!!!!!!!
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    Uv radiation, gamma radiation, mutagenic chemicals, viruses
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    A gene mutation occurs when there is a change in the sequence of bases in the dna formming the coding part of the gene.

    There are 3 different types of gene mutation-:

    -Addition & Deletion- These both have a drastic affect on organism
    When one base is added or lost from the sequence of bases. This causes a frameshift and all the triplet codes (codons) after the mutation are changed and so different amino acids will be used to make the polypeptide.

    -Substitution- This usually has the least affect on the organism
    This is changing/swapping one base for another. It doesnt have as much affect as addition and deletion do. Changing one base means that only one codon is affected. Sometimes this change has little or no affect on the organism. Because the dna code is degenerate.


    You've also got other sources of variation like-

    Polygenic inheritance- This is when there are several genes that code for the same characteristic,

    Meiosis generates genetic variation-
    Crossing over - occurs at prophase I. This is when homologous chromsones associate. They may cross over. This produces a new mixture of genetic material.
    Independant Assortment - occurs at metaphase I & II. Bivalents and chromsones line up at the equator of the spindle randomly. Depending on how they lines up different combinations end up at the poles. This results in a different mixture of maternal and paternal chromsones/chromatids in daughter cells.
 
 
 
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