Topic 8-Genetic mutations Flashcards
What is a gene mutation?
a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide (that the gene codes for)
How do mutations occur?
continuously and spontaneously
When do mutations usually occur?
In DNA replication
Most mutations do not alter the polypeptide or only alter it slightly so that its structure or function is not changed, why is this?
Because the genetic code is degenrate
Mutations in the DNA base sequence can occur due to what? (Nucleotide/gene)
-Insertion, deletion or substitution of a nucleotide
-Inversion, duplication or translocation of a section of a gene
What do insertions and deletions mutations change?
changes the amino acid that would have been coded for by the original base triplet-creates a new, different triplet of bases
Do insertion and deletions mutations have a knock on effect (by changing the triplets further down the DNA sequence)
Yes
What are frameshift mutations? Give some examples of what can cause them?
-Mutations that change the amino acid sequence produced from this gene and therefore the ability of the polypeptide to function
-Insertions, deletions
What is a deletion mutation?
when a nucleotide (and therefore its base) is randomly deleted from the DNA sequence
What is a substitution mutation?
when a base in the DNA sequence is randomly swapped for a different base
What is a difference between deletions +insertions and substituitions?
only change the amino acid for the triplet (group of three bases) in which the mutation occurs; it will not have a knock-on effect
What are the 3 forms of substituition mutations?
Silent mutations – the mutation does not alter the amino acid sequence (because genetic code is degenrate)
Missense mutations-mutation alters a single amino acid
Nonsense mutations-mutation creates a premature stop codon, causing an incomplete polypeptide chain, effecting the final structure and function
When do inversion of a gene section usually occur?
crossing-over in meiosis
What happens during an inversion?
-DNA of a single gene is cut in two places
-cut portion is inverted 180° then rejoined to the same place within the gene
- result= large section of the gene is ‘backwards’ and therefore multiple amino acids are affected
What do inversion mutaions frequently result in?
A non functional protein (sometimes an entirely different protein is produced)
Why are inversion mutations particularly harmful?
he original gene can no longer be expressed from that chromosome (although if another chromosme carries that working gene the effect may be lessend)
What is a duplication of a gene?
A whole gene or section of a gene is duplicated so that two copies of the gene/section appear on the same chromosome
Why are duplication genes not harmful?
original version of the gene remains intact
Overtime, the second copy can undergo 1.______ which enable it to develop new 2._______
1.mutations
2.functions
Why are duplication muations an important?
-source of evolutionary change
What is a translocation of a gene?
-gene is cut in two places
-section of the gene that is cut off attaches to a separate gene
-result= cut gene is now non-functional due to having a section missing and the gene that has gained the translocated section is likely to also be non-functional
What happens if a section of a proto-oncogene is translocated onto a gene controlling cell division?
-Boosts expression and leads to tumors
What happens if a section of a tumour suppressor gene is translocated?
result= a faulty tumour suppressor gene, this could lead to the cell continuing replication when it contains faulty DNA
