D1.3 Flashcards
Mutations and Gene Editing
Define gene mutations
Structural changes or alterations in the DNA sequence of an organism.
List the causes of gene mutations
Proofreading errors in DNA replication or transcription.
Physical- UV radiation
Chemical- Cigarette smoke, Nitrate preservatives
Infectious agent- HPV
Distinguish between substitutions, insertions and deletions
Substitution- of one nucleotide with another
Insertion- of one or more nucleotides into a DNA sequence
Deletion- of one or more nucleotides from a sequence
Define single nucleotide polymorphism
An SNP represents a variation at a single base-pair position in the DNA sequence of an individual. It occurs when a single nucleotide (A, T, C, or G) is substituted by another. These changes can manifest within both coding (gene-containing) and non-coding regions of the genome.
Describe the consequences of base substitutions
Single-nucleotide polymorphisms (SNPs) are the result of base substitution mutations and that because of the degeneracy of the genetic code they may or may not change a single amino acid in a polypeptide.
Describe the consequences of insertions and deletions
Include the likelihood of polypeptides ceasing to function, either through frameshift changes or through major insertions or deletions.
Outline the impact of genetic code degeneracy on the effect of mutations
Due to the genetic code’s degeneracy, multiple codons can encode for a single amino acid. Thus, a change in one codon might still produce the same amino acid. In such cases, even though a substitution has occurred, it doesn’t alter the amino acid or the protein’s function, hence termed as a ‘silent’ mutation.
Distinguish between same sense, nonsense and mis sense base substitution mutations
Mis-sense: change alters a single amino acid in a protein change (sickle cell anemia)
Nonsense: Change creates a premature STOP codon which leads to shorter polypetide (Cystic Fibrosis)
Define frameshift mutation:
A frameshift mutation in a gene refers to the insertion or deletion of nucleotide bases in numbers that are not multiples of three
Outline the consequences of insertions and deletions on polypeptide structure and function
The change in reading frame alters every amino acid after the point of the mutation and results in a nonfunctional protein.
Define mutagen
A mutagen is an agent that induces a permanent change to the genetic material of an organism
Discuss the impact of randomness of gene mutations
Mutations can occur anywhere although some bases have a higher probability of mutating than others. No natural mechanism is known for making a deliberate change to a particular base with the purpose of changing a trait.
Distinguish between germ cells and somatic cells
Germ cells are the cells responsible for the sexual reproduction of new organisms. Regular body cells that repair and reproduce tissues are known as somatic cells.
Compare the consequences of a germ cell versus somatic cell mutation
Germline mutations can be transmitted to offspring and every cell in the offspring will have the mutations meaning they are inheritable. Somatic mutations have little effect on the organism because they are confined to one cell and its daughter cells.
Define genetic variation.
Variation results from small differences in DNA base sequences between individual organisms within a population.
Discuss gene mutation as the original source of all genetic variation.
Although most mutations are either harmful or neutral for an individual organism, in a species they are in the long term essential for evolution by natural selection.
State the source of new alleles of a gene
Mutation is a source of new alleles in a population.
Distinguish between beneficial, neutral, and harmful gene mutations
The ‘good’ or advantageous that increase fitness, the ‘bad’ or deleterious that decrease it and the ‘indifferent’ or neutral that are not affected by selection because their effects are too small.
State the function of gene knockout studies.
Investigating the function of a gene by changing it to make it inoperative.
Outline the method scientists use to knockout genes
designing a guide RNA (gRNA) that targets a specific location in the genome,
delivering the gRNA and a Cas9 enzyme (which acts as a molecular scissors) to the target cell, and then allowing the cell to repair the cut in the DNA.
Describe the process of gene editing using CRISPR Cas9
Uses a guide RNA to match a desired target gene, and Cas9 (CRISPR-associated protein 9)—an endonuclease which causes a double-stranded DNA break, allowing modifications to the genome
Outline the ethical implications of gene editing
Some of the ethical dilemmas of genome editing in the germline arise from the fact that changes in the genome can be transferred to the next generations.
Define conserved sequence of DNA
Identical or similar sequences across a species or a group of species.
List common examples of the products coded for by conserved sequences of DNA
Examples of such sequences include those that lead to DNA replication, transcription and translation, and proteins involved in cellular respiration
State two hypotheses that account for conserved sequences between species
One is that the functional requirements of the gene are those that the organism cannot survive without
The other is that some sequences of DNA are subject to slower mutation rates
