DNA Mutations

Question 1

Explain ‘gene mutation’.

Answer 1

Change in sequence of bases in DNA of a gene

Question 2

Explain ‘ chromosomal aberration’.

Answer 2

Change to chromosome structure or change to chromosome number

Question 3

Transition mutation

Answer 3

Replacement of purine/pyrimidine base with another purine/pyrimidine base

Question 4

Transversion mutation

Answer 4

Replacement of purine/pyrimidine base with pyrimidine/purine base

Question 5

Missense mutation

Answer 5

• results in codon encoding different amino acid

- polypeptide produced is altered in structure and function

Question 6

Silent mutation

Answer 6

• alteration of one codon to another, that still encodes for the same amino acid (due to degeneracy of geentic code)
• no observable effect on phenotype

Question 7

Neutral mutation

Answer 7

• alteration of one codon to another, that encodes for a different amino acid
• no effect on phenotype, no detectable change in protein
• could have occured in part that is non-essential to protein structure and function, or replacement with amino acid with another having similar properties

Question 8

Nonsense mutation

Answer 8

• change codon to a stop codon

- production of truncated polypeptide and thus non-functional protein

Question 9

Frameshift mutation

Answer 9

• nucleotide-pair insertion or deletion causes shift in reading frame; codons downstream improperly grouped into triplets, altering amino acid sequence
• may cause generation of premature stop codon
• non-functional proteins unless it occurs at/near end of gene

Question 10

Define: Aneuploidy

Answer 10

Chromosomal abberation in which one or more chromosomes are present in extra copies or deficient in number

Question 11

Define: Polyploidy

Answer 11

Condition of the nucleus where there are 3 or more complete sets of chromosomes

Question 12

Types of polyploidy

Answer 12

• Autopolyploidy

- Allopolyploidy

Question 13

Define: Autopolyploid

Answer 13

Contains more than 2 chromosome sets derived from SINGLE species

Question 14

Define: Allopolyploid

Answer 14

Contains multiple sets of chromosome sets derived from TWO OR MORE species, forming a hybrid

Question 15

Explain how gene mutations result in sickle cell anaemia.

Answer 15

• single nucleotide substitution in 6th DNA triplet on non-coding DNA strand for β chain of haemoglobin, changing CTT to CAT
• when transcribed, mRNA’s 6th codon altered from GAA to GUA; GAA encodes glutamic acid while GUA encodes valine
• thus, polypeptide of resultant β-globin chain has non-polar, hydrophobic valine instead of polar glutamic acid
• presence of valine makes HbS less soluble; at low O2 concentrations, when O2 is released, valine forms hydrophobic patch that fits into hydrophobic pocket in other haemoglobin molecules
• haemoglobin containing the abnormal β-globin HbS has altered quaternary structure that causes haemoglobin molecules to polymerise and form rigid rod-like fibres that distort red blood cells, making them sickle-shaped