D3.1 Mutation and Gene Editing

Question 1

Gene mutation

Answer 1

A permanent, random, and structural change in the base sequences of the DNA.

Question 1

Define point mutation

Answer 1

A single base substitution resulting in a change in the codon of the mRNA.

Question 1

What happens in the mutation of the HOX gene of a fruit fly?

Answer 1

Legs sprout on the foreheads instead of antennas.

Question 2

What are the consequences of point mutations?

Answer 2

If a mutation occurs in the non-coding region, then it is unlikely to have any effect.

Question 3

Silent base substitution

Answer 3

Base substitution that does not change the AA sequence due to the degeneracy of the code (multiple codons can code for the same AA)

Question 4

Missense mutations

Answer 4

• Causes the expression of a different AA.
• The AA is either functional or dysfunctional depending on its type.

Question 5

Nonsense mutation

Answer 5

• Substituted base is a stop codon hence, it results into a shortened polypeptide
• Either functional or dysfunctional.

Question 5

Frameshift mutation

Answer 5

• The deletion and insertion of nucleotides in the gene sequences.
• Resulting in a completely different AA sequence.
• Results in a dysfunctional polypeptide

Question 6

Define insertion

Answer 6

Insertion of a nucleotide –> extra base sequence in the gene.

Question 7

Define deletion

Answer 7

removal of a nucleotide –> one less base sequence in the gene.

Question 8

CCR5 gene & Delta 32: HIV infection resistant

Answer 8

• To enter cells, the HIV-1 virus must bind to the CCR5 receptor on the surface of the WBC.
• Homozygous carriers of Delta 32 become resistant to HIV infection.
• Delta 32 causes the deletion of a portion of the CCR5 gene, making it dysfunctional.
• Therefore, it makes the person resistant to the HIV infection.

Question 8

Reasons for the randomness of genetic mutation

Answer 8

• They can occur anywhere in the base sequences of a gene.
• Some bases have a higher chance of mutating.
• The position of a base within a gene.

Question 8

Huntington’s disease

Answer 8

• The HTT gene on chromosome 4 that codes for the Huntingtin protein experiences frameshift mutation.
• Normal huntingtin gene: has several repeats of CAG.
• Mutated huntingtin gene: one or several insertions of additional CAG sequences.
• Results in neural degeneration in the brain hence, causes neurological dysfunctions.

Question 9

What are the two causes of gene mutations?

Answer 9

1. Errors in DNA replication
2. Mutagens:

• Radiation (UV and X-rays)
• Chemicals: cosmetics, carcinogens.
• Infectious agents: bacteria & viruses.

Question 10

How does mutation affect GERMLINE cells?

Answer 10

Definition: reproductive cells where one haploid cell becomes gametes.

• These mutations are heritable and can be passed on.
• They appear in all body cells within the organism.

Question 10

How does gene mutation result in genetic variation?

Answer 10

• It increases the number of different alleles of genes in a population.
• Original source of all GV and are essential for the continuity of the population despite, it being potentially harmful.

Question 10

How does mutation affect SOMATIC cells?

Answer 10

• Definition: diploid body cells used to produce specialized cells.
• These mutations have limited consequences.
• Mutation is eliminated when the individual dies. (does not get passed on)

Question 11

Single nucleotide polymorphism (SNPs)

Answer 11

• They are found in both coding and non-coding regions.
• A type of allele that differs by only one nucleotide.
• Due to degeneracy of the code –> may or may not change the AA sequence in a polypeptide.