BI111 Lecture Notes - Lecture 1: Frameshift Mutation, Nonsense Mutation, Silent Mutation

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9 Feb 2017
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Read units 36-39, 32, 45, 46 and 48 for this week
DNA as repository of genetic information
DNA is a language, every cell contains info how they build, copy, prepare themselves
Encoded in a polynucleotide chain in a "language" with 4 "letters
Linked by a sugar phosphate backbone, adenine with thymine, guanine with cytosine
DNA replication is quite accurate- instructions aren't corrupted from one sequence to another
Mutations are not necessarily a bad thing
Mutation Rates
Vary within and between taxa
Vary with environmental conditions
o In some environments mutation rates are higher
Higher in RNA viruses (10-3 to 10-5 mutation base -1 generation01) than in DNA viruses (10-6 to 10-8)
Higher in mitochondrial DNA (3x10-6 to 2.7x10-5) than in genomic DNA (2.5x10-8)
Higher in asexual species than sexual species
In humans 1.1x10-8 mutations, per site per generation
On the Road to the Phenotype
Introns removed from Pre-mRNA before translation
Alternate mRNA transcripts created by selective slicing/arrangement of exons
Translation involves taking particular string of letters and reading them 3 letters at a time
The genetic code has both specificity and redundancy
Genetic code was established very early in the evolution of life and has remained unchanged
Nonsense mutation means a mutation occurs that results in a stop codon being prematurely called
upon(missing a big part of sequence)
Silent mutation codons call for the same amino acid and switching one letter does not change the
amino acid being called for
Frameshift mutation which involves the deletion or addition of one or more base pairs into a
particular sequence
Mutations can affect phenotypes
Sometimes even a very simple mutation can have a huge impact on a phenotype
In hemoglobin which is made up of many proteins, single mutation is responsible for sickle celled
Many alleles, varying affects on phenotype
Two copies of the same allele, mother and father both donated either big a or little a and are
Homo(same)zygous(sperm or egg)
Two copies of different alleles, small a and big A are Heterozygous because there is a mismatch
between the two matches
Manx cats
Mutation originated in populations of cats on the Isle of Mann
Tailless mutation is dominant and homozygous lethal
Different Types of Genes
1)All white fur controlled by "White Masking" gene
W-dominant all white hair
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