9.1 Gene Mutations

Question 1

What is a mutation?

Answer 1

Any change to the quantity or the base sequence of the DNA of an organism

Question 2

What is a gene mutation?

Answer 2

Any change to one or more nucleotide bases or a change in the sequence of bases in DNA

Question 3

What are the 2 types of gene mutations?

Answer 3

• base substitution
• base deletion

Question 4

What is base substitution? Give an example

Answer 4

• the replacement of one nucleotide with a different nucleotide
  Eg. T -> A

Question 5

Why is it that not all base substitution mutations lead to a change in the amino acid sequence?

Answer 5

• degenerate nature of the genetic code means that some amino acids are coded for more than one DNA triplet
• not all substitution mutations will result in a change in the amino acid sequence of the protein as some will still code for the same amino acid

Question 6

What is a mutagenic agent?

Answer 6

An outside factor that increases the rate of mutations

Question 7

Give three examples of a mutagenic agent and its effect on a mutation

Answer 7

1. High ionising radiation - disrupts the DNA sequence
2. Nitrogen dioxide - disrupts the structure of DNA and interferes with transcription
3. Benzopyrene - inactivates a tumour suppressor gene TP53 and causes cancer

Question 8

What is a chromosome mutation?

Answer 8

Change in the structure or number of whole chromosomes

Question 9

What are the two forms of chromosome mutation?

Answer 9

• polyploidy
• non-disjunction

Question 10

What is polyploidy?

Answer 10

• changes in whole sets of chromosomes
• occurs when organisms have 3 or more sets of chromosomes rather than 2
• mostly happens in plants

Question 11

What is non-disjunction?

Answer 11

• changes in individual numbers of chromosomes
• homologous pairs will fail to separate during meiosis
• results in a gamete having either one more of one fewer chromosome
• individuals could have an additional chromosome number 21 resulting in Down Syndrome