Week 7 Flashcards
how many mutations cause adaptation?
Only a few mutations will be beneficial and contribute to adaptation
Only a few change proteins
Only a few proteins change phenotype
Only a few phenotypes increase fitness
what are mutations?
Existing difference in the DNA sequence present in a population
Or can be the verb of DNA changing
Mutant vs wildtype
Some are inherited (in germ line) some are only in individual (soma)
what causes mutation?
Genome replication and repair - errors
Mutagens - UV light, cigarettes etc. repair of this damage causes mutations
types of replication error
Non-synonymous substitution (new amino acid coded for by swapping one nucleotide)
Synonymous substitution (does not change amino acid - most likely if change is to third position of the codon)
Insertion or deletion - causes reading frameshift
evolution
the change in frequencies of alleles/mutations/genetic variants in a population over time.
Can’t happen without mutation
how do new genes evolve?
Large duplication or deletion
Evolutionary benefit - gene dosage: can result in making more of a gene product
Can lead to evolution of new genes
subfunctionalisation
one gene that had two functions evolves into two genes, each with a single function
neofunctionalisation
one gene evolves into two genes, at least one of which evolves a new function with a single function. One gene gets a totally different function.
where new alleles come from
Mutations can arise as a result of alterations to DNA that escape repair before or during replication or because of errors that occur during replication itself and escape repair afterward
Spontaneous deamination - cytosines can read with water to become thymines
Mutation by misalignment - the template and DNA strand can slip out of register at repeat sites, resulting in duplications and deletions
how do mutations alter protein function?
Point mutations
Transitions and transversions
Substitutions
Insertions and deletions (together called indels)
When introns are not spliced out
where do new genes come from
Unequal crossing over - one chromosome ends up with a deletion and the other with a duplication
Retroposition or retroduplication - when a DNA segment formed by reverse transcriptase is inserted into the cell’s DNA
evolution of DDT resistance
Insecticide resistance in drosophila and other insects
Change in DDT resistance by modifying cytochrome P450
Insecticide resistance did not emerge until 1950s because insecticides were not wildly used
evolution can happen by deleting genes
Fish that live in caves losing eyes
how do we detect duplication events?
Sequence alignment
Can see how long ago a duplication happened by looking at the similarity in nucleotide sequences
fitness effects of mutations
Beneficial - lactase persistence after the age of 5
Neutral
Deleterious
selection coefficients
Measures the strength of selection acting on a genotype
Time to fixation is proportional to strength of selection
We can calculate fitness by measuring the change in frequency over a number of generations
