mutations gene: frame shift mutation (deletion) · mutations may or may not affect phenotype •...
TRANSCRIPT
Key Point: Some mutations affect a single gene, while others affect an entire chromosome.others affect an entire chromosome.
Ch l M t ti• A mutation is a change in an organism’s DNA:
Gene Mutations
Where: DNA
Chromosomal Mutations
Where: Chromosome
When: during crossingWhen: during replication.
1. Point Mutation
When: during crossing over.
1 Gene Duplication2. Frame Shift Mutation
(deletion or insertion)
1. Gene Duplication
2. Gene Translocation
Gene: Point Mutations
DNA
mRNA
fi d l id i b i d f h
Amino acids
Defined: one nucleotide is substituted for another• Often repaired by spellchecker enzymeM l d t i id h• May lead to amino acid change– See animation
• May not lead to any change (Silent Mutation)• May not lead to any change (Silent Mutation)– Ex: DNA “CCC” is mutated into “CCG”
» Same amino acid is created (glycine)
Gene: Frame Shift Mutation (deletion)
DNA
mRNA
Amino acids
Defined: Insertion/deletion of a nucleotide• Entire sequence of DNA/RNA after the mutation is shiftedEntire sequence of DNA/RNA after the mutation is shifted (see animation)
• Much more serious to the structure/function of the final protein– mRNA sequence may have early or late “stop codons”
Gene: Frame Shift Mutation (insertion)
DNA
mRNA
A iAmino acids
Chromosome: Gene Duplication
Defined: a section of a gene is repeated. • Results from unequal crossing over.• Can affect many genes and the overall chromosome structure.
Chromosome: Gene Translocation
Defined: When a section of a gene is repeatedDefined: When a section of a gene is repeated. • Results from the exchange of DNA segments between non‐homologous chromosomes.g
Mutations May or May Not Affect Phenotype• Some gene mutations change phenotype.
• Some gene mutations do not affect phenotype.
– May cause a premature stop codon.
– May be silent.
– May occur in a noncoding– Can change protein structure.
region.
– May not affect protein structure.
blockage
no blockage
Impact on OffspringS ti ll t ti G ll t ti• Somatic cell mutations– Affect only the individualNot passed on to future
• Germ cell mutations– May be passed to future generations (either– Not passed on to future
generations– Ex: Muscle cell mutation
generations (either harmful or beneficial)
– Ex: Sperm cell mutationEx: Muscle cell mutation p
• Natural selection often removes mutant alleles from a population when they are less adaptive.
Mutation Causes
• Mutagen: agents in the environment that can change DNA– Speed up replication process– Speed up replication process
– Break apart nucleotides
• Ex: UV sunlight breaks hydrogen bond between thymine (T) g y g yand adenine (A)