Mutations Flashcards
(21 cards)
What is a mutation (definition)?
When a change occurs to the sequence of bases in DNA. A mutation may involve a change to a single base, a group of bases, part of a chromosome or and entire chromosome. These changes to DNA sequences can occur during DNA replication, protein synthesis and DNA repair. OR changes to chromosomes occur during mitosis or meiosis.
Point Mutations
Involve changes to a single nucleotide base in the DNA sequence
Point Mutations (substitution)
One base is replaced by another. There are three types of substitutions:
- Silent Mutation
- Missense Mutation
- Nonsense Mutation
Silent Mutation
The change does not affect the protein because the new codon codes for the same amino acid.
Missense Mutation
The change results in the substition of one amino acid for another in the protein.
Nonsense Mutation
The change results in a premature stop codon, which truncates the protein.
Insertion Mutations
A nucleotide or a sequence of nucleotides is added to the DNA sequence. This can shift the reading frame (frame-shift mutation), potentially altering the entire protein after the mutation.
Deletion Mutations
A nucleotide or a sequence of nucleotides is removed from the DNA sequence. Like insertions, deletions can cause frame-shift mutations if the number of nucleotides removed is not a multiple of three.
3 Answers
Effects of Frameshift Mutations
- Can drastically alter the amino acid sequence after the mutation site.
- Often results in a nonfunctional protein or an early stop codon.
- More severe than substitution mutations since they disrupt the entire coding sequence.
Duplication Mutations
A segment of the DNA sequence is duplicated, leading to multiple copies of that segment in the genome. This can alter the function of genes and proteins.
Inversion Mutations
A segment of the DNA sequence is reversed, meaning that the order of the nucleotides in that section is flipped. This can disrupt the function of genes within that segment.
Chromosomal Mutations
These affect the structure or number of chromosomes.
Types of chromosomal mutations
Deletion: Loss of a chromosome segment (e.g. Cri-du-chat syndrome)
Duplication: Segment is copied and inserted (e.g. Charcot-Marie-Tooth disease)
Inversion: Segment is reversed within the chromosome
Translocation: Segment moves to a different, non-homologous chromosome
Nondisjunction: Chromosomes fail to separate during meiosis → results in extra or missing chromosomes (e.g. Down syndrome, Turner syndrome)
Frameshift Mutations
These occur when the insertion or deletion of nucleotides shifts the reading frame of the codons in the mRNA. It often leads to a completely altered protein that might not function correctly.
Why do genetic mutations often occur during cell division?
- DNA Replication errors
- Crossing over during mitosis
- Chromosomal segregation errors
- DNA damage from environmental factors
DNA Replication Errors
Cell Division Mutations
DNA polymerase can make mistakes during replication, such as adding the wrong base or skipping a base (while proofreading mechanisms often correct these errors, they sometimes slip through).
If these errors occur in a gene or a regulatory region of DNA, they can cause a mutation.
Crossing over during Meiosis
Cell Division Mutations
In meiosis, the process that produces reproductive cells, homologous chromosomes exchange genetic material during a process called crossing over.
- Sometimes, the chromosomes don’t align properly during crossing over, which can lead to deletions, duplications or inversions in the DNA. These changes can cause mutations.
Chromosomal Segregation Errors
Cell Division Mutations
During Cell Division, chromosomes must seperate properly to ensure that each daughter cell gets the correct number of chromosomes.
- Errors in this process, known as nondisjunction, can result in cells with too many or too few chromosomes.
- This can lead to aneuploidy, where a cell has an abnormal number of chromosomes (e.g. down syndrome).
Non-disjunction
Cell Division Mutations
The failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
DNA Damage from environmental factors
Cell Division Mutations
External factors like radiation (e.g. UV light or X-rays), chemicals (e.g. carcinogens), or certain viruses can cause DNA damage.
- The DNA damage may not always be repaired correctly, leading to mutations. For example, UV light can cause thymine dimers (when two adjacent thymine bases bond together), which, if not repaired can result in mutations.
- High temperatures can destabilize DNA and increase the chances of errors during replication.
Block Mutations
A segment of a chromosome is changed (the same as a chromosomal mutation)
