D1.3 Mutation and gene editing Flashcards
gene mutation
a change in the sequence of bases of a particular gene
when do mutations occur
all the time and at random
inheritance of mutations
Mutations present in normal body cells are not inherited, they are eliminated from the population once those cells die
Mutations within gametes are inherited by offspring, possibly causing genetic disease
what is a mutation
the process of dna replication is complex and mistakes occur sometimes
point mutation
change in one base in the gene sequence
can be the result of
substitution mutation
insertion
deletion
substitution mutations
where one nucleotide is replaced by a different nucleotide
caused by DNA being copied incorrectly
insertion mutations
addition of one or more nucleotides into a segment of dna
deletion
the loss of one or more nucleotides from a segment of DNA
Frameshift Mutations
A mutation in a DNA chain that occurs when the number of nucleotides inserted or deleted is not a multiple of three, so that every codon beyond the point of insertion or deletion is ready incorrectly during translation
what can frameshift mutations be caused by
insertions or deletion as these processes alter the reading Frame of codons
same sense mutation
change one codon for an amino acid into another codon for the same amino acid
AGC becomes AGT
nonsense mutation
change a codon that codes for an amino acid into a stop codon
translation is therefore terminated before a polypeptide has been completed
stop codons - UAA, UAG, UGA
mis sense mutation
alter one amino acid in the sequence of amino acid in a polypeptide
eg, sickle cell disease
SNPs full form
single nucleotide polymorphisms
what are SNPs
silent mutations which does not alter the amino acid sequence
when DNA from individuals humans is sequenced, large numbers of base substitutions are found that have happened at some time in the past
where can SNPs occur
in noncoding regions of DNA
Insertions can result in
repeating base sequences of 3 nucleotides expanding tri nucleotide repeat sequences
tri nucleotide repeat disorders
caused due to an abnormal number of triplet repeat sequences
Huntingtons Disease - HTT
caused by an abnormality in HTT gene
Mutated dominant allele
Deletion example
delta 32 mutation of CCR5 gene
what does deletion prevent
functional expression of CCR5 protein co-receptor normally used by HIV -1 to enter CDU + T-cells
HIV can no longer bind to this co-receptor and so cannot efficiently enter checks
Mutagenic agents
environmental factors that increase the mutation rate of cells
Radiation
can cause chemical changes in DNA, this includes:
High-energy radiation such as UV light
Ionising radiation such as X-rays, gamma rays and alpha particles
Chemical substances effect and example
can cause changes to DNA, examples include
nitrosamines found in tobacco smoke
Mustard gas used as a chemical weapon in World War I
ionising radiation examples
gamma rays, x rays, alpha particles
non-ionising radiation examples
UV radiation
random mutation
more likely to occur at certain times in cell cycle such as during DNA replication
can occur anywhere in base sequences of a genome
Transition substitution mutation
swaps between bases of similar shape
between 2 ringed purines and 2 ringed pyridines
Transversions substitution mutation
Swaps between a purine and pyramidine base
why are Transition substitution mutation more common
they keep same ring shape and structure
less likely to occur in amino acid substitutions
what is the most common mutation
sequence CG because both involve 3 hydrogen bonds to pair with the base on the opposite strand
when happens if there is a mutation in germ cells
if a mutation occurs in a germ cell it can be passed on to the offspring and next generation
what are germ lines
Cells involved in inheritance of genetic information, eggs, sperm and zygote
what could A mutation that occurs in sperm cells do
potentially affect the zygote of that offspring and all cells developed from that zygote will contain the mutation
somatic cell
any biological cell forming the body of a multicellular organism other than a gamete
what does cancer arise due to
Cancers demonstrate how important it is that cell division is precisely controlled, as cancers arise due to uncontrolled mitosis
are mutations harmful
most mutations are either harmful or neutral
use of mutation
without mutation genetic variation would decline over time
used for genetic variation so species can evolve
