Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Chapter 19: Gene mutation, DNA repair, and recombination
1
,Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
- Mutation = a heritable change in the genetic material structure of DNA is changed
permanently and can be passed from mother cell to daughter cells, and sometimes even
from parent to offspring
- Can be beneficial, neutral or detrimental
- Random mutations are more likely to disrupt these sequences
- DNA repair systems can reverse damaged DNA
- Homologous recombination = the process whereby identical or similar DNA segments
are exchanged between homologous chromosomes. During crossover in meiosis
19.1: Effects of mutations on gene structure and functions
Gene mutations are molecular changes in the DNA sequence of a gene
- Point mutation = change in a single base pair within the DNA
o Base substitution = one base is substituted for another
Transition = pyrimidine to pyrimidine (C/T)
Transversion = purine and pyrimidine interchanges
Gene mutations can alter the coding sequence within a gene
- Effects of point mutations
o Silent mutations – do not alter the sequence, genetic code is degenerate
o Missense mutations – amino acid change. Example = sickle cell disease
mutation in B-globin gene 6th amino acid from glutamine to valine. Low oxygen
= sickle cell shape
o Nonsense mutations – change from amino acid codon to a stop codon
truncated polypepitde
o Frameshift mutations – addition/deletion of a number of nucleotides not
divisible by 3 other reading frame, completely different polypeptide
o Neutral mutation when a missense mutation has no detectable effect on protein
function. Silent mutations are also neutral mutations
2
, Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Gene mutations can occur outside of a coding sequence and influence gene expression
- Mutation can occur in a non-coding region, affecting gene expression
- May alter the sequence in the core promoter of a gene
o Up promoter mutation – increase the rate of transcription, more like consensus
sequence
o Down promoter mutation – decrease the rate of transcription, less like
consensus sequence
- IRE regulates translation and RNA stability mutations in 5’UTR of ferritin mRNA may
alter the IRE sequence, affecting the translation of the mRNA
- Mutations in eukaryotes can alter splice recognition sequences, affecting the
order/number of exons contained within an mRNA
Gene mutations are also given names that describe how they affect the wild-type genotype
and phenotype
- Wild-type = prevalent genotype
- Mutation may change this genotype by altering the DNA sequence of a gene. Rare
mutation? result = mutant allele
- Reversion = reverse mutation = changes mutant allele back to wild-type allele
- Deleterious mutation – decreases the changes of survival and reproduction lethal
mutation or beneficial mutation
- Sometimes a mutated allele can be deleterious or beneficial sickle cell
- Conditional mutants – phenotype is affected under a defined set of conditions.
Temperature-sensitive ts mutant defective growth at the nonpermissive range
Suppressor mutations reverse the phenotypic effects of another mutation
- A second mutation can affect the expression of a first mutation
- Suppressor/suppressor mutations act to suppress the phenotypic effects of another
mutation
- Differs from reversion, it occurs at a different site in the DNA from the first mutation
o Intragenic suppressors
Second mutation site is within the same gene as the first
Change in protein structure that compensates for an abnormality in
protein structure caused by the first mutation
o Intergenic suppressors
Suppressor mutation occurs in a different gene than the one of the first
mutation
Change in the expression of one gene that compensates for a loss-of-
function mutation
They sometimes have effect on multimeric proteins, in which each subunit
is encoded by a different gene
Mutations in genetic regulatory proteins like transcription factors
mutant transcription factor can activate another gene that can
compensate for the loss-of-function mutation in the first gene
3
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Chapter 19: Gene mutation, DNA repair, and recombination
1
,Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
- Mutation = a heritable change in the genetic material structure of DNA is changed
permanently and can be passed from mother cell to daughter cells, and sometimes even
from parent to offspring
- Can be beneficial, neutral or detrimental
- Random mutations are more likely to disrupt these sequences
- DNA repair systems can reverse damaged DNA
- Homologous recombination = the process whereby identical or similar DNA segments
are exchanged between homologous chromosomes. During crossover in meiosis
19.1: Effects of mutations on gene structure and functions
Gene mutations are molecular changes in the DNA sequence of a gene
- Point mutation = change in a single base pair within the DNA
o Base substitution = one base is substituted for another
Transition = pyrimidine to pyrimidine (C/T)
Transversion = purine and pyrimidine interchanges
Gene mutations can alter the coding sequence within a gene
- Effects of point mutations
o Silent mutations – do not alter the sequence, genetic code is degenerate
o Missense mutations – amino acid change. Example = sickle cell disease
mutation in B-globin gene 6th amino acid from glutamine to valine. Low oxygen
= sickle cell shape
o Nonsense mutations – change from amino acid codon to a stop codon
truncated polypepitde
o Frameshift mutations – addition/deletion of a number of nucleotides not
divisible by 3 other reading frame, completely different polypeptide
o Neutral mutation when a missense mutation has no detectable effect on protein
function. Silent mutations are also neutral mutations
2
, Genetics summary – VU BMS 2020/2021
Simone Zweers
Reference: Brooker, Genetics: Analysis and prinicples, 7th edition
Gene mutations can occur outside of a coding sequence and influence gene expression
- Mutation can occur in a non-coding region, affecting gene expression
- May alter the sequence in the core promoter of a gene
o Up promoter mutation – increase the rate of transcription, more like consensus
sequence
o Down promoter mutation – decrease the rate of transcription, less like
consensus sequence
- IRE regulates translation and RNA stability mutations in 5’UTR of ferritin mRNA may
alter the IRE sequence, affecting the translation of the mRNA
- Mutations in eukaryotes can alter splice recognition sequences, affecting the
order/number of exons contained within an mRNA
Gene mutations are also given names that describe how they affect the wild-type genotype
and phenotype
- Wild-type = prevalent genotype
- Mutation may change this genotype by altering the DNA sequence of a gene. Rare
mutation? result = mutant allele
- Reversion = reverse mutation = changes mutant allele back to wild-type allele
- Deleterious mutation – decreases the changes of survival and reproduction lethal
mutation or beneficial mutation
- Sometimes a mutated allele can be deleterious or beneficial sickle cell
- Conditional mutants – phenotype is affected under a defined set of conditions.
Temperature-sensitive ts mutant defective growth at the nonpermissive range
Suppressor mutations reverse the phenotypic effects of another mutation
- A second mutation can affect the expression of a first mutation
- Suppressor/suppressor mutations act to suppress the phenotypic effects of another
mutation
- Differs from reversion, it occurs at a different site in the DNA from the first mutation
o Intragenic suppressors
Second mutation site is within the same gene as the first
Change in protein structure that compensates for an abnormality in
protein structure caused by the first mutation
o Intergenic suppressors
Suppressor mutation occurs in a different gene than the one of the first
mutation
Change in the expression of one gene that compensates for a loss-of-
function mutation
They sometimes have effect on multimeric proteins, in which each subunit
is encoded by a different gene
Mutations in genetic regulatory proteins like transcription factors
mutant transcription factor can activate another gene that can
compensate for the loss-of-function mutation in the first gene
3
