Wright 11 - Mutations and Phenotype

Question 1

What is a mutation?

Answer 1

A permanent change in the hereditary material (ie. DNA)

Question 2

What two types of cells can mutations occur in?

Answer 2

• Somatic cells of multicellular organisms

- Germ-line cells, eg. sperm or eggs

Question 3

What is a translocation mutation?

Answer 3

A type of chromosomal rearrangement where a portion of genes switch in heterologous chromosomes

Question 4

What two types of point mutations are there?

Answer 4

• Base substitutions

- Insertion or deletion of nucleotides

Question 5

What is a transition base substitution?

Answer 5

A purine to a purine or a pyrimidine to a pyrimdine

Question 6

What is a transversion base-substitution?

Answer 6

A purine to a pyrimidine or a pyrimidine to a purine

Question 7

What is a silent point mutation?

Answer 7

No effet on amino acid sequence

Question 8

What is a missense point mutation?

Answer 8

Where one amino acid is changed

Question 9

What is a nonsense point mutation?

Answer 9

Where an early stop codon is coded for, resulting in a truncated polypeptide

Question 10

What are three consequences that could come out of a missense mutation?

Answer 10

1. Neutral (no affect on function of the polypeptide)
2. Radical loss of function
3. Radical gain-of-function

Question 11

What is an intragenic supressor mutation?

Answer 11

Where a first mutation is suppressed by a second mutation in the same gene.

Question 12

What is an intergenic supressor mutation?

Answer 12

Where a first mutation is suppressed by a second mutation in a different gene.

Eg. a first mutation causes an enzyme to have an active site that won’t bind to its substrate. A second mutation causes the substrate to be complementary to the mutated enzyme, and therefore function is restored. Obviously, this is rare, but it does and has happened.

A second mutation can also occur for the transfer RNA, where the anticodon loop is altered so that is uses the original amino acid that was coded for (but changed in the first mutation).

Question 13

Can mutations be spontaneous with no chemical or physical agents?

Answer 13

Yes

Question 14

What are three types of spontaneous mutations?

Answer 14

• Tautomeric shifts during DNA replication (eg. a proton shift leading to non-standard base pairing arrangements)
• DNA strand-slippage during DNA replication
• Misalignment of homologous chromosomes during crossing over (recombination) at meiosis I

Question 15

What are anomalous base-pairing arrangements?

Answer 15

Where the rare, tautomerized forms of base pairs pair with common forms. Eg. rare form cytosine with common form adenine.

Question 16

How does a slipped-strand mispairing cause an insertion in DNA synthesis?

Answer 16

A newly synthesized strand loops out resulting in the addition of one extra nucleotide on the new strand.

Key is that the new strand loops out for an insertion

Question 17

How does a slipped-strand mispairing cause a deletion in DNA synthesis?

Answer 17

A template strand loops out resulting in the omission of one nucleotide on the new strand.

Key is that the template strand loops out for a deletion

Question 18

What does misalignment of homologous chromosomes during crossing over at meiosis cause?

Answer 18

One crossover product with an insertion and one with a deletion