3.4.3 Genetic diversity can arise as a result of mutation or during meiosis

Question 1

Gene mutations

Answer 1

A change in the DNA base sequence of chromosomes - any change to one or more nucleotide bases or any rearrangement of bases in DNA

Question 2

What stage of the cell cycle do gene mutations arise spontaneously?

Answer 2

DNA replication –> Synthesis Phase of Interphase

Question 3

Why might a mutation not lead to change in the amino acid sequence?

Answer 3

• Genetic code is degenerate: mutation may end up coding for the same amino acid as the original triplet
• Mutation may occur in intron (non-coding for polypeptides)

Question 4

What are the factors that contribute to the likelihood of mutations?

Answer 4

• High energy radiation (X-rays, gamma rays)
• High energy particles (ionized and radioactive energy particles)
• Mutagenic agents/carcinogens (e.g tar in cigarette smoke)

Question 5

What is a substitution mutation?

Answer 5

When a nucleotide in the DNA sequence is replaced by another.

Question 6

In regards to substitution mutation, what are the three types of mutations as a consequence?

Answer 6

• Silent mutation
• Mis-sense mutation
• Nonsense mutation

Question 7

What is a silent mutation?

Answer 7

No change in the amino acid (same amino acid as the original triplet)

Question 8

What is a nonsense mutation?

Answer 8

A stop codon is produced

Question 9

What is a mis-sense mutation?

Answer 9

A different amino acid is produced.

Question 10

Describe the effect that a mis-sense mutation has on the formation of a protein?

Answer 10

• Different amino acids —> different protein produced
• Primary structure is affected
• Secondary structure is affected: different R-groups/H-bonds/ionic bonds/disulphide bridges.
• Tertiary structure is affected – folding of protein

Question 11

What is a deletion mutation?

Answer 11

When a nucleotide is lost from the original DNA sequence

Question 12

What is a frame shift?

Answer 12

When ALL the amino acids after the point of mutation will be in the wrong triplet

Question 13

Why is a deletion mutation more harmful and significant than a substitution mutation?

Answer 13

Frame shift means the entire amino acid sequence will be different

Question 14

What is an addition mutation?

Answer 14

When a nucleotide is added to the original DNA sequence –> frame shift changing the entire amino acid sequence after the point of mutation

Question 15

What are mutagenic agents?

Answer 15

Factor that increase the rate of gene mutation

Question 16

What are chromosome mutations?

Answer 16

Errors during meiosis with the gametes produced containing variations in the numbers of whole chromosomes or parts of chromosomes

Question 17

What is chromosome non-disjunction?

Answer 17

Pairs of chromatids that do not separate in meiosis, resulting in gametes with one more or one less chromosome than normal

Question 18

What are the examples of non-disjunction disorders?

Answer 18

• Down syndrome: extra chromosome 21
• Patau’s syndrome: extra chromosome 13
• Edward’s syndrome: extra chromosome 18
• Kleinfelters
• Turners