1.3 Mutations and Gene Editing

Substitution mutation (point mutation)

A mutation that occurs when a nucleotide base in the DNA sequence is randomly swapped for a different base

Insertion mutation (frameshift mutation)

A mutation that occurs when a nucleotide is randomly inserted into the DNA sequence

Deletion mutation (frameshift mutation)

A mutation that occurs when a nucleotide is randomly deleted from the DNA sequence

Causes of gene mutations

Mutagenic agents such as radiation from UV light, gamma rays, or X-rays, and chemical substances such as carcinogens or processed foods and preservatives

Silent base substitution

When the DNA change does not alter the amino acid sequence of the polypeptide

Missense base substitution

When the DNA change alters a single amino acid in the polypeptide chain

Nonsense base substitution

When the DNA change creates a premature stop codon which shortens the polypeptide

Randomness of mutations

Mutations can occur anywhere in the base sequence of a genome, however some locations are more likely to mutate than others

Is there a natural mechanism for making a deliberate change?

No

Single nucleotide polymorphisms (SNPs)

A germline substitution of a nucleotide at a specific position in the genome. They are found in non-coding regions of DNA. They act as biological markers, helping to locate genes associated with disease

Consequences of insertions and deletions

Frameshift mutations can change the entire amino acid sequence of a polypeptide, causing it to cease to function

Mutations in germ cells

Germ cells are cells used in reproduction, so if a mutation occurs in a germ cell it is passed on to offspring

Mutations in somatic cells

Somatic cell mutations are not inherited by offspring, instead these mutations are associated with cancers

What is the source of genetic variation?

Mutation. It results in the generation of new alleles, which can influence the evolution of a species by natural selection, leading to variation

Genome

The complete set of genetic information in an organism

Gene knockout

The use of genetic engineering to remove or inactivate a specific gene and study the effects to understand the gene’s function

Common knockout organisms

Mice

Steps of CRISPR

1. A specific gene is identified and a guide RNA is designed to match its sequence

2. The guide RNA is added to the cell along with the Cas9 enzyme

3. The guide RNA binds to the target sequence and Cas9 cuts the DNA

4. Another piece of DNA is added, which replaces the removed segment

Conserved sequences

A sequence that is identical or very similar across all members of a species or a group of species

Highly conserved sequences

Sequences that are identical or similar over long periods of evolution

Hypotheses for conserved sequences and highly conserved sequences

1. The functional requirements of the gene are those that the organism cannot survive without

2. Some sequences of DNA are subject to slower mutation rates