9.1 Gene mutation

Question 1

What is a mutation?

Answer 1

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

Question 2

What is a gene mutation?

Answer 2

Any change to the nucleotide bases or the sequence of bases.

Question 3

What is substitution?

Answer 3

A type of gene mutation where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base.

Question 4

What is the effect of a substitution mutation?

Answer 4

• if the substitution changes the amino acid that a triplet codes for, then the polypeptide produced will differ in a single amino acid.
• the significance of the depends on the role of the AA
• if it is involved in forming bonds that determine the tertiary structure of the protein, then the replacement may not form the same bonds and the structure will be entirely different
• if the substitution does not change the amino acid (can occur as the genetic code is degenerate) then the mutation will have no effect.

Question 5

What is deletion?

Answer 5

When a nucleotide is lost from the normal DNA sequence

Question 6

What is the effect of deletion?

Answer 6

• the polypeptide structure is different and so it cannot function properly
• as the sequence is read in units of three, it will be read differently because each has been shifted to the left.

Question 7

What is a chromosome mutation?

Answer 7

Changes in the structure or number of whole chromosomes.

Question 8

Describe the two forms of chromosome mutation.

Answer 8

1) CHANGES IN WHOLE SETS OF CHROMOSOMES: occur when organisms have 3+ sets of chromosomes rather than the usual 2. this is called polyploidy (usually occurs in plants)
2) CHANGES IN THE NUMBER OF INDIVIDUAL CHROMOSOMES: if individual homologous pairs of chromosomes don’t separate during meiosis, non-disjunction occurs and the individual has either one more or one fewer chromosomes.