Unit 1: Human Cells: Chapter 4: Mutations Flashcards
Mutation
A change in the structure of composition of an organisms genome. Varies from tiny change in DNA structure if a gene to large scale alteration in chromosome structure of number.
Mutant
An individual affected by a mutation, when a change in genotype caused by mutation also produces a change in phenotype.
Frequency of mutation
Expressed as number of mutations that occur at that gene site per million gametes.
Without influence of external factors, mutations occur spontaneously, randomly & rarely.
Mutagenic agents
Include certain chemicals (mustard gas), and various types of radiation ( gamma rays, X-rays, Uv light). Resultant mutations are described as INDUCED.
Genetic disorder
A condition or disease that is directly related to an individual’s genotype.
Single gene mutation
Alteration of a nucleotide sequence in a gene’s DNA
- point mutation
- splice site mutation
Point mutation
Type of single gene mutation involving a change in 1 nucleotide in DNA sequence of a gene. There are 3 types of point mutation.
- substitution
- insertion
- deletion
All result on 1+ codons for 1+ amino acids being altered.
Splice site mutation
Alteration of splice site nucleotide sequence on parts of introns which flank exon. Mutation at splice sites may result in introns being left in or exons being left out of mature transcript of mRNA.
Impact on protein structure: Missense
Change on genome caused by mutation where coding for an amino acid still makes sense but not the original sense.
See case studies on Sickle Cell disease & PKU
Impact on protein structure: Nonsense
Codon that used to code for an amino acid is substituted for one that acts as a premature stop codon. Protein synthesis is halted early, resulting in formation of shorter polypeptide chain which is unable to function.
Impact on protein structure: splice-site mutation
One or more introns retained in mature mRNA transcript, creating an altered protein that cannot function properly.
See case study on beta thalassaemia
Impact on protein structure: frameshift
mRNA read as series of triplets ( codons) during transcription. If a base pair is inserted or deleted, the reading frame (triplet grouping) of the genetic code is shifted in a way that alters every subsequent codon & amino acid coded along the remaining length of the gene. Protein formed will almost certainly be non functional.
Allele
Variations of a specific gene
Homozygous
Individual is said to be homozygous for a gene if he/she receives 2 identical copies of a gene, 1 from each parent.
Heterozygous
Individual is said to be heterozygous for a gene if he/she receives 2 different alleles of a gene, 1 from each parent.
Chromosome structure mutations
Involve the breakage of one or more chromosomes. Broken end of chromosome is sticky & can join to another broken end.
Chromosome structure mutations: deletion
Occurs when chromosome breaks in 2 places. Segment in between becomes detached, 2 broken ends join to form a shortened chromosome which lacks certain genes. Usually has drastic effect on organism concerned.
Chromosome structure mutations: duplication
Segment of genes becomes attached to one end of the first chromosome or inserted somewhere along its length. Results on a set of genes being repeated.
Cancer is common cause of duplication.
Chromosome structure mutations: translocation
Section of chromosome breaks off f becomes attached to different chromosome i.e. NOT it’s homologous partner. Most common type of mutation associated with cancer.
See case study on CML
Chromosome structure mutations: inversion
A chromosome breaks in 2 places. The segment in between flips over before rejoining the broken chromosome again. This causes a reversal of normal gene sequence & is often fatal.
See case study on Haemophilia A
