D1.3 Mutations and Gene editing

Gene knockout

A genetic engineering technique used for investigating the function of a gene by making it inoperative

Knockout organism

An organism whose genes have been knocked out

Mutation

A random, rare change in genetic material

Substitution mutation

A mutation that results in a single nucleotide base in DNA is swapped for a different base

Single Nucleotide Polymorphism

When a gene sequence is altered by one nucleotide base (via insertion, deletion, or substitution)

Missense mutation

Mutation that alters a single amino acid in the polypeptide chain

Nonsense mutation

A substitution mutation that results in a premature STOP codon, creating a non-functional protein

Same-sense mutation

a mutation that does not alter the amino acid sequence of the polypeptide

Insertion mutation

When a nucleotide (with a new base) is randomly inserted into the DNA sequence

Deletion mutation

When a nucleotide (and therefore its base) is randomly deleted from the DNA sequence

Frameshift mutation

When an insertion of deletion occurs in non-multiples of three

Mutagens

Chemicals that can cause a genetic mutation

Mutagenic agents

Environmental factors that increase the mutation rate of cells

Mutation hotspots

Regions where mutations are more frequent

CpG site

Locations where the nucleotide cytosine is followed by guanine

• If methylated, C mutates into Thymine (T) in a substitution mutation

• A CpG island is where this occurs frequently, and is associated with colorectal cancer

Outline the consequences of mutations in germ cells

• Mutations in germ cells can be passed onto offspring and the next generation since they are involved in the germ line

• Mutation in sperm cells can affect the zygote, and all cells developed from that zygote will contain the mutation

• A female who has inherited a mutation will contain the mutation in the germ cells of their ovaries which are passed onto future offspring

Outline the consequences of mutations in somatic cells

• Mutations in somatic cells are associated with cancer and tumours, but are not passed down

• Will affect the organ that the mutated cell is found

• All cells in the tumour will have the mutation, and may metastasis

Genome

The entire set of genetic material of an organism

Gene therapy

The treatment of a genetic disease by altering the person’s genotype

Explain the process of CRSIPR-Cas9

CRISPR Cas9 is a gene-editing technique that allows for precise modifications of a genome

• DNA double helix with mutation

• Guide RNA is created to match the mutated DNA

• Cas9 is added to guide RNA mixture and injected into cells

• Guide RNA identifies mutated DNA

• PAM sequence is required for Cas9 to bind to mutated DNA, where it then cuts out mutated sequence

• This causes a break in the target DNA

• If the cell effectively repairs the break, the targeted gene is silenced

• Faulty gene replaced by correct DNA or new sequence

Gene drive

Mechanism that increases the chances of a gene being passed on to the next generation

Conserved sequences

Gene sequences in DNA or RNA that show minimal mutations over time

Highly conserved sequences

Genetic sequences in DNA or DNA that show no or almost no changes over long periods of evolution

• sequences for DNA replication, transcription, translation, proteins involved in cellular respiration

State two hypothesises for highly conserved sequences

1. Functional requirements - highly conserved sequences exist in genes that code for proteins vital for an organisms survival. Without such processes, the cell would cease to survive. Natural selection maintains highly conserved sequences by necessity via purifying selection

2. Slower mutation rates- some zones of gene sequences are less prone to mutations and the mutation rate is slower than in other sequences. Locations with fewer mutation rates have mutations that are spotted and corrected more frequently hence do not appear in sequenced DNA

Mutation rate

How many changes there is to the DNA sequence over time

• Number of base pairs changing in a single gene at each generation/ cell division

• Number of base pairs changing in whole genome per generation