Mutations. Mutation- a change in the DNA nucleotide sequence Mutations can be silent, cause subtle, or dramatic effects on observed traits in individuals. Observed trait. DNA. mRNA. protein. translation. protein function (enzyme activity). transcription.
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Mutations Mutation- a change in the DNA nucleotide sequence Mutations can be silent, cause subtle, or dramatic effects on observed traits in individuals
Observed trait DNA mRNA protein translation protein function (enzyme activity) transcription How does your DNA determine your traits? • Remember: • Traits are determined by the functions of proteins • Protein function is determined by protein shape • Protein shape is determined by amino acid sequence
Mutations can change the amino acid sequences of proteins DNA sequence: T A C C G A G A T T C A mRNA sequence: A U GG C UC U AA G U amino acid sequence: Met -- Ala -- Leu -- Ser DNA sequence: T A C C G A G A T T C A mRNA sequence: A U GG C UA U AA G U amino acid sequence: Met -- Ala -- Iso -- Ser T
How does this mutation change the amino acid sequence? (Original) DNA sequence: A A T G C A T A T G C A mRNA sequence: U U AC G UA U AC G U amino acid sequence: Leu -- Arg -- Ile -- Arg (Mutated) DNA sequence: A A T T C A T A T G C A mRNA sequence: U U AA G UA U AC G U amino acid sequence: Leu -- Ser -- Ile -- Arg
3 types of mutations Substitution Insertion Deletion T T A C C G A G A T T C A Substituting one nucleotide for another. T A C C G A T G A T T C A Inserting one or more nucleotides T A C C G A G A T T C A Deleting one or more nucleotides
Your Turn • Complete the “Mutations practice” worksheet. You will learn how some mutations can affect the amino acid sequence of proteins • Consider how severe of an effect each mutation would have on the ability of the protein to function.
Question: • We’ve studied transcription, translation, and replication. A mistake in which of these processes would result in a permanent mutation?
Which type of mutations had the biggest effect on the protein sequence? WHY? • Which type of mutations had the smallest effect on the protein sequence? WHY? • Which examples would you predict to have the biggest effects on a trait? WHY? • Which examples would you predict to have the smallest effects on a trait? WHY?
Different types of mutations happen Substitution Insertion Deletion T T A C C G A G A T T C A T A C C G A T G A T T C A T A C C G A G A T T C A
Frameshift mutations • One or more than one nucleotide can be added or deleted with insertion and deletion mutations. • If the number of nucleotides is not a multiple of 3, it is called a frameshift mutation. • Why do we call this a frameshift mutation? • Can substitution mutations cause frameshifts? Explain why or why not.
Consequences of mutations… • If a mutation in sperm or egg DNA is not corrected, the new sequence of DNA is passed on to offspring. • Over generations, more mutations accumulate. • As a result, differences occur between people’s DNA sequences!
How much variation in DNA exists between 2 people? Hemoglobin (beta) gene sequence from person A
How much variation in DNA exists between 2 people? Hemoglobin (beta) gene sequence from person B
How much variation in DNA exists between 2 people? • About 1 in every 1,000 nucleotides is different between 2 people • (0.1% difference means 99.9% identical) • We have about 3 billion nucleotides in all, so that means there are about 3 million nucleotide differences between 2 people
What is the observed effect of mutations? • No Effect (think about it: are there 3 million differences between 2 people?) • Why? • Some mutations code for the same amino acid • Most mutations are in sequences of DNA between genes. • Variation – there are a variety of traits in a population.
Genetic diseases • Many alleles are harmless, but some can cause specific diseases. • To determine whether a disease is genetic, we trace the family history of a disease by creating a type of family tree called a pedigree. • One disease caused by a specific mutation is sickle cell anemia