Readings 5 notes

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University of Toronto Scarborough
Biological Sciences
Maydianne Andrade

Readings 5 Pgs.143-166 -meoisis reshuffles existing alleles into new combinations -mutation is the only process that creates new alleles and new genes (source of genetic variation) -adenine and guanine are purines (two) while cytosine and thymine are pyrimidines (one) -a single strand of DNA consists of a sequence of bases attached to sugar-phosphate groups that form a backbone -purine-pyrimidine combinations are called complementary base pairs -because 20 amino acids need to be specified by 64 codons of the genetic code, the genetic code is redundant in that the same amino acid can be specified by more than one codon -genes are defined as stretches of DNA that code for RNA or a protein -alleles are defined as versions of the same gene that differ in their base sequence -mutations are defined as any type of change in base sequence of DNA -altering a single point in the base sequence of a gene is called a point mutation -point mutations are caused by random errors in DNA synthesis or random errors in the repairing of sites damaged by chemical mutagens or radiation -if DNA polymerase mistakenly substitutes a purine for another purine, the point mutation is called transition (most common) -if a purine is substituted for a pyrimidine or a pyrimidine for a purine, the point mutation is called transversion -changes in the first or second position of a codon almost always lead to a change in the amino acid specified by the resulting mRNA -point mutati
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