Mutations (la mayoría es de triple)

Mutation

They are rare, random changes in the sequence of DNA bases in a gene or a chromosome that can be inherited

Mutations can be _____

They occur ____

Inherited

Continuously

What is the POSSIBLE effect of a mutation?

Mutations in a gene may lead to a gene coding for the wrong amino acid(s) and as a result, the wrong protein.

• Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed

TRIPLE:

How does a change in DNA (a mutation) affect the phenotype?

Altering the sequence of amino acids in a protein

Whar are the main ways that a mutation can occur (sequence of bases changed)?

• Insertion

• Deletion

• Substitution

What is insertion? How will this affect the sequence of bases?

A new base in randomly inserted

• It changes the amino acid that would have been coded for by the original codon

• Also will have a knock-on effect by changing the codons for the rest of the DNA sequence (codes for an entirely new protein)

What is deletion? How will deletion affect the sequence of bases?

A base is randomly deleted

• It changes the amino acid that would have been coded by the original codon

• Also will have a knock-on effect by changing the codons for the rest of the DNA sequence (codes for an entirely new protein)

What is substitution? How will deletion affect the sequence of bases?

A base in the DNA sequence is randomly swapped for a different base

• Unlike an insertion or deletion, a substitution mutation will only change the amino acid for the group of three bases in which the mutation occurs.

• There is NO knock-on effect

What are inversions?

The sequence of bases in a triplet is reversed.

The effects are similar to substitution: no knock on effect, only one triplet affected and this may or may not result in a diff amino acid and altered protein structure

Hay que tener en cuenta de que mutations may or not have an effect on the phenotype (function or appearance) porque por ejemplo, podrías tener un substitution mutation y el nuevo codon vaya a code for the same amino acid que antes.

Most genetic mutations have zero/small/big effect on the phenotype

Some genetic mutations have zero/small/big effect on the phenotype

Rarely genetic mutations have zero/small/big effect on the phenotype

Zero

small

big

Occasionally, what can mutations create?

New alleles, resulting in new phenotypes

Remember that mutations can be advantageous or harmful.

If the mutation is very harmful, the cell will die and the mutation will be ___

Lost

When the organism dies and it doesn’t reproduce (or the offspring doesn’t inherit the allele), the mutation is lost

A scientist discovers a mutation in the skin cells of a lizard that causes its scales to glow dark. Over several generations, none of the lizard’s offspring show this trait.

Why does the glowing scale mutation not appear in the offspring, even though the original lizard lived long and reproduced successfully?

Because the mutation occurred in body (somatic) cells (skin), not in the gametes. Somatic mutations affect only the individual and are not passed to offspring

Body cells include heart, intestines, skin

Remember that only mutations in the gametes (sex cells) or in the cells that divide to form gametes can be passed on to the next generation — gametes contain DNA that will be passed on to the next generation

This is how genetic diseases begin

How can the incidence/frequency of mutations increase?

• Exposure to ionising radiation (gamma rays, x-rays and UV rays): they damage bonds and cause changes in base sequences

• Chemical mutagens (mustard gas and nitrous oxide, chemicals in cigarette tar and smoke)

• Increased rates of mutation can cause cells to become cancerous, which is why the above are linked to increased incidence of different types of cancer