Mutations

Question 1

Description of gene mutation

Answer 1

• definition: involves a (1) permanent heritable change
  (2) in one or a few bases in the nucleotide/base sequence
  (3) of one gene
• could be the substitution of one nucleotide pair with another
• resulting in missense / neutral / silent / nonsense mutation
• could also be the addition or deletion of one or more nucleotide pair
• which if not in multiples of 3, will result in a frame shift mutation
• where all nucleotides downstream of insertion/deletion site will be improperly grouped into codons
• resulting in extensive missense mutation
• which if in multiples of 3, will result in missense / nonsense mutation

Question 2

elaboration of missense mutation (in nucleotide sub)

Answer 2

• results in a different mRNA codon
• causing the translation of a different amino acid
• leads to a change in aq seq
• leads to change in 3d conformation
• thus leads to change in protein function

Question 3

elaboration of missense mutation (in nucleotide insertion or deletion)

Answer 3

• results in mRNA codon being added or deleted
• causing the polypeptide to have an amino acid added or deleted
• leads to a change in aq seq
• leads to change in 3d conformation
• thus leads to change in protein function

Question 4

elaboration of nonsense mutation (in nucleotide sub)

Answer 4

• results in a stop codon
• causing premature termination of translation
• truncated protein -> non-functional

Question 5

elaboration of silent mutation (in nucleotide sub)

Answer 5

• results in a different mRNA codon
• causing the translation of the same aa
• leads to same aa seq
• leads to same 3d conformation
• thus no change in protein function

Question 6

elaboration of nonsense mutation (in nucleotide insertion or deletion)

Answer 6

• results in stop codon being added
• causing a truncated protein
• truncated protein -> non-functional

Question 7

Description of chromosomal aberration (structure)

Answer 7

• definition: change in the structure of a chromosome
• which results in reshuffling of alleles on chromosome

Deletion:
- when chromosome breaks in one or more places,
and a portion of it lost
- missing part is referred to as a deletion

Duplication:
- when any part of the genetic material, be it a single locus or a large piece of chromosome,
is present more than once in the genome
- due to unequal crossing over between synapses chromosomes during meiosis /
through a replication error prior to meiosis

Inversion:
- when a segment of a chromosome is turned around 180º within a chromosome

Translocation:
- is the movement of a chromosomal segment to a new location in the genome

Question 8

Description of chromosomal aberration (no.)

Answer 8

• definition: a change in the number of chromosomes

aneuploidy:
- where there is addition or loss of one or more chromosomes

polyploidy:
- where there is addition of one or more haploid sets of chromosomes
- resulting in autopolyploidy if additional sets of chromosomes come from same species
- or resulting in allopolyploidy if additional sets of chromosomes come from different species
- due to non-disjunction / failure of chromosomes or chromatids
to disjoin and move to opp poles during division

Question 9

How chromosomal aberration results in Down syndrome

Answer 9

• gain of an extra chromosome 21 (X chromosome)
• but not a complete set
• due to non-disjunction / failure of chromosomes or chromatids to disjoin and move to opp poles
• during anaphase I of meiosis I or anaphase II of meiosis II
• disrupting normal distribution of chromosomes into gametes
• forming abnormal gametes containing two members of the affected chromosome
• fertilising these with a normal haploid gamete produces a zygote with 3 members of this chromosome

Question 10

Symptoms of Down syndrome

Answer 10

• characteristically short
• stocky bodies / thick necks
• low intelligence level
• short life expectancy

Question 11

elaboration on how mutation may change structure and function of protein

Answer 11

• change in 3d conformation of protein
• change in R grp interactions (HI or hydrogen bonds)
• change in the binding/interaction of protein with other molecules

Question 12

differences between GOF mutation and LOF mutation

Answer 12

• no of mutations (needed for effect on phenotype)
  
  • GOF: single mutation
  • LOF: 2 mutations
• type of allele
  
  • GOF: dominant allele
  • LOF: recessive allele
• effect
  
  • GOF: activates/stimulates process
  • LOF: inactivates process
• example
  
  • GOF: oncogene
  • LOF: tumour suppressor gene

Question 13

differences between chromosomal and gene mutations

Answer 13

• extent
  
  • chromosomal: may involve transfer of whole genes
  • gene: change in base
• effect
  
  • chromosomal: changes regulation / control of expression of gene
  • gene: changes protein produced

Question 14

when does mutations have no effect on activity of enzyme

Answer 14

• silent mutations which result in no change in aa seq
  OR neutral mutation where change in aa is to another with similar properties
• mutations that could result in a change in aa in a region away from binding site of enzyme
• thus does not affect conformation / binding properties of binding site