B1 Mutations And Genetic Variants

Question 1

What happens when DNA mutate?

Answer 1

A random change occurs in the DNA, which alters the sequence of bases within the molecule.

Question 2

How are all genetic variants formed?

Answer 2

By mutations

Question 3

Name 3 ways the mutations can change the DNA base sequence.

Answer 3

Insertion
Deletion
Substitution

Question 4

What happens when a DNA base sequence is changed by insertion?

Answer 4

A new base is inserted into the DNA sequence where it shouldn’t be.

Question 5

Insertions can change more than one amino acid, what effect does this have on the sequence?

Answer 5

There is a knock on effect on the bases further on in the sequence.

Question 6

What does an insertion change?

Answer 6

The way the triplets are read, which can change the amino acids they code for.

Question 7

What happens when a DNA sequence is changed by deletion?

Answer 7

A random base is deleted from the DNA base sequence.

Question 8

How does deletion affect the base sequence ?

Answer 8

It changes the way the base sequence is read and has a knock on effect further down the sequence.

Question 9

What happens in a substitution?

Answer 9

A random base in the DNA base sequence is changed to a different base.

Question 10

What effect does substitution have on the amino acids?

Answer 10

Some amino acids are coded for by more than one triplet, so substitution mutations don’t always change the amino acids in a protein.

(Eg tyrosine is coded for by TAT and TAC

Question 11

If a mutation leads to a change in the amino acid sequence coded for by a gene, what could this change?

Answer 11

The structure and function of the final protein

Question 12

What does a change in the structure and function of the final protein mean?

Answer 12

The protein might work differently or it may stop working altogether.

Question 13

What are enzymes?

Answer 13

Proteins that speed up chemical reactions in an organism

Question 14

How might a mutation affect how an enzyme works?

Answer 14

A mutation in the gene that codes for an enzyme might result in the enzymes shape changing so that it is no longer able to perform its function.
(Enzymes have to be a specific shape to work properly)

Question 15

How can the change in the function of a single protein effect a phenotype?

Answer 15

Occasionally the change cases a big effect such as the genetic disorder cystic fibrosis.

Question 16

How is the genetic disorder cystic fibrosis caused?

Answer 16

Can be caused by the deletion of just three bases.

The gene codes for a protein that controls the movement of salt and water into and out of cells. In the protein produced by the cystic fibrosis genetic variant doesn’t work properly.

This leads to excess mucus production in the lungs and digestive system.

Question 17

What are the difficulties associated with the excess mucus production for a person with cystic fibrosis genetic variant?

Answer 17

Difficulty breathing and digesting food.

Question 18

What happens if a mutation in coding DNA doesn’t change the amino acid sequence?

Answer 18

The mutation will have no effect on the protein structure or function and no effect on the phenotype.

Question 19

Some mutations only slightly alter protein function, what does this do to the phenotype?

Answer 19

This leads to a very small effect on the phenotype.

Question 20

What is non coding DNA?

Answer 20

DNA that doesn’t code for any amino acids.

Question 21

What do non coding DNA do?

Answer 21

Some non coding DNA parts switch genes on and off, so they control whether a gene is expressed (used to make a protein)

Question 22

What happens if there is a mutation in non coding DNA?

Answer 22

Non coding DNA may prevent a protein from being produced, which may affect the organisms phenotype.

Question 23

Explain why a gene mutation may affect the phenotype of an organism (3 marks)

Answer 23

A gene mutation alters the base sequence of DNA in a gene (1 mark)
Which may affect the order of the amino acids in the protein produced (1 mark)
This may lead to changes in the structure and function of the protein, which may alter the phenotype (1 mark)