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Summary Genetics Chapter 19
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Chapter 19Mutation Heritable change in the genetic material and also used for the genetic changes in somatic cells, think of
mutations in cancer cells. Provide allelic variation:
On the positive side, mutations are the foundation for evolutionary change needed for a
species to adapt to changes in the environment
On the negative side, new mutations are much more likely to be harmful than beneficial to
the individual and often are the cause of diseases
Since mutations can be quite harmful, organisms have developed ways to repair damaged DNA.
Three main 1. Chromosome mutations: Changes in chromosome structure (deletions, duplications, inversions,
types translocations,)
2. Genome mutations: Changes in chromosome number (aneuploidy, euploidy)
3. “small’ mutations: 1 up to a few bases: Relatively small changes in a DNA sequence (base order)
that occur within a particular gene or its promoter.
Mutations Indels: insertions, deletions
change DNA Mutations may also involve the addition or deletion of short
sequence sequences of DNA.
Point mutations = change in a single base pair -> involves base substitution.
- A transition is a change of a pyrimidine (C, T) to another pyrimidine or a purine (A, G) to another
purine
- A transversion is a change of a pyrimidine to a purine or vice versa
Transitions are more common than transversions
Gene silent mutation:
mutations can genetic code is
alter the degenerate (third
coding base).
sequence
within a gene Neutral mutation:
when missense
mutation has no
detectable effect
on protein
function (or/and
silent mutations).
Missense
mutation: sickle
cell disease.
Glutamic acid -> valine. Single substitution has profound effect on phenotype of cell and even causes
serious disease.
Mutation in Can still effect gene expression:
noncoding 1. A mutation, may alter the sequence within a
sequences promoter
- Up promoter mutations make the promoter
more like the consensus sequence. They may
increase the rate of transcription
- Down promoter mutations make the promoter
less like the consensus sequence. They may
decrease the rate of transcription
Mutation can alter splice junctions in eukaryotes.
Example mutation in operator: lacOc -> prevented
binding of lac repressor, causes lac operon to always be expressed even if lactose is not present. Energy
, waste.
Gene In a natural population, the wild-type is the relatively prevalent genotype.
mutations - A forward mutation changes the wild-type genotype into some new variation
and their - A reverse mutation changes a mutant allele back to the wild-type: It is also termed a reversion
effect on (rare)
genotype and
phenotype Mutation can also be described based on their effects on the wild-type phenotype: when a mutation alters
an organism’s phenotypic characteristics, it is said to be a variant or mutant. Variants are often
characterized by their differential ability to ‘survive’, but it is not only survival.
- Deleterious mutations decrease the chances of survival -> The most extreme are lethal mutations
- Beneficial mutations enhance the survival or reproductive success of an organism
>> Some mutations are called conditional mutants
They affect the phenotype only under a defined set of conditions -> An example is a temperature-sensitive
mutation
Mutations in Germ-line mutations: mutations in
germ-line cells: cells that give rise to
gametes such as eggs and sperm: occur
directly in a sperm or egg cell, or in one
of their precursor cells.
Somatic mutations: mutations in
somatic cells (all other cells): occur
directly in a body cell, or in one of its
precursor cells.
Genetic mosaic.
Random Mutations can occur spontaneously or be induced.
nature of Spontaneous mutations: Result from abnormalities in cellular/biological processes. Errors in DNA
mutations replication during ‘cell division’ and DNA repair.
Induced mutations: Caused by environmental agents: Agents that are known to alter DNA structure
Rates of are termed mutagens: These can be chemical or physical agents
spontaneous
mutation per
cell
generation
typically
range from
10-5 to 10-9.
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