Mutations And Variation

What is a mutation?

A change in the sequence of bases in DNA.

What might happen if a mutation occurs within a gene?

Protein synthesis may be stopped.

What is the change in sequence caused by?

The substitution, deletion, or insertion of one of more nucleotide (or base pairs) within a gene.

What is it called if only one nucleotide is affected by the mutation?

A point mutation.

What does the substitution of a single nucleotide change?

The codon in which it occurs. If the new codon codes for different amino acid, this will lead to a change in the primary structure of the protein.

What does the degenerate nature of the genetic code mean for substitution mutations?

That the new codon may still code for the same amino acid, leading to no change in the protein synthesised.

In a substitution mutation, what determines the impact of the new amino acid on the function of the protein?

The position and involvement of the amino acid in R group interactions within the protein. For example, if the protein is an enzyme and the amino acid plays an important role in the active site, the protein may no longer act as a biological catalyst.

What does the insertion or deletion of a nucleotide lead to?

A frameshift mutation. The triplet code means that base sequences are transcribed consecutively in non-overlapping groups of three. The addition or deletion of a nucleotide moves or shifts the reading frame of the sequence of bases. This changes every successive codon from the point of mutation.

What are the different effects of mutation?

• No effect.

• Damaging.

• Beneficial.

What does it mean if a mutation has no effect?

There is no effect on the phenotype of the organism because normally functioning proteins are still synthesised.

What does it mean if a mutation is damaging?

The phenotype of an organism is affected in a negative way because proteins are no longer synthesised or proteins synthesised are non-functional.

What does it mean if a mutation is beneficial?

Very rarely, a protein is synthesised that results in a new and useful characteristic in the phenotype.

How do mutations usually occur?

Mutations can occur spontaneously, often during DNA replication.

What is the rate of mutation increased by?

Mutagens.

What are mutagens?

A chemical, physical, or biological agent which casues mutations.

How does the loss of a purine base (depurification) often occur?

Spontaneously.

What can the absence of a base lead to?

The insertion of an incorrect base through complimentary base pairing and during DNA replication.

What can free radicals (oxidising agents) affect?

The structures of nucleotides and also disrupt the base pairing during DNA replication.

What is the ability to digest lactose, present in milk, thought to be?

The result of a relatively recent mutation.

When do the majority of mammals become lactose intolerant?

After they cease to suckle.

Where is the ability to digest lactose primarily found?

In European populations who are more likely to farm cattle. The ability to drink milk as an adult helps prevent diseases like osteoporosis. This could also have prevented individuals with the mutation from starving.

Where do gene mutations occur?

In single genes or sections of DNA.

What do chromosome mutations affect?

The whole chromosome or a number of chromosomes within a cell. They can also be caused my mutagens and normally occur during meiosis.

What do changes in chromosome structure include?

• Deletion.

• Duplication.

• Translocation.

• Inversion.

What is deletion in a chromosome?

When a section of chromosome breaks off and is lost within the cell.

What is duplication in a chromosome?

When sections get duplicated on a chromosome.

What is translocation on a chromosome?

When a section of one chromosome breaks off and joins with another non-homologous chromosome,

What is inversion on a chromosome?

When a section of chromosome breaks off, is reversed, and then joins back onto the chromosome,