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Chapter 4

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Larry Moran

BCH 447 lecture 4 Mutation or the creation of new alleles is the underlying cause of evolution. The minimal definition of evolution is the fixation of an allele within the population. But in the long run mutation is important. And therefore mutation rates are important. Human beings are a good model organism for understanding mutation rates. Biochemically... What is the mutation rate. In that, how many mutations does a new born child have that are different from its parents. Ultimately all mutations come from an error in DNA replication. What would be the mutation rate in humans with fundemental information. So, sperm, from zygote to maturity divide 400 times. While eggs multiply about 30. So at the end we have 430 replication cycles before we are made. Now there is 3.2x10^9 nucleotides per haploid The replication machinery makes a mistakes at 1x10^-10... This is 1x10^-6 for the polymerase. 1x10^-2 proof reading. And 1x10^-2 repair. As such the answer is. # of nucleotides x mistakes per run x 430 divisions. This gives us about 138 mutations. The percent of the mutations that are deleterious is extremely low. This is because 97% of the genome is noncoding. For protein coding genes. 1/3 of all mutations that occur in a protein coding gene are deleterious. If we have 130 mutations and we are running 1/3 of the mutations are deleterious we are looking at 42 deleterious mutations. This means that every time we have progeny the progeny would carry 42 deleterious and lethal mutations. This is called genetic load... It is the number of deleterious mutations that occur i
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