Chapter 12 : Variation part 2

Question 1

Types of mutation :

Answer 1

gene mutation / chromosomal mutation

Question 2

Definition of gene mutation :

Answer 2

Change in the structure of gene

Question 3

Definition of chromosomal mutation:

Answer 3

Change in the structure of chromosome / change in the chromosome number

Question 4

What does gene mutation alters?
(base sequence/genetic code/amino acid)

Answer 4

Gene mutation alters the base sequence of a gene in the DNA, hence altering the genetic code in the mRNA to synthesise amino acid for protein sysnthesis.

Question 5

Ways of changing the base sequence:

Answer 5

Base substitution / Base deletion / Base insertion

Question 6

Base substitution:
Explain?
What happened to amino acid and sequence?

Answer 6

A base is replaced by another base in the DNA.
This will change on codon, thus only changing one amino acid.
The rest of the amino acids remain unchanged.
Hence the sequence of the amino acid is changed and a non-functional protein is produced.

Question 7

Base insertion:

Answer 7

A new base is inserted into the DNA.
This changes the sequence of the codon starting from the point of insertion, thus changing the sequence of amino acid and a non-functional protein is produced.

Question 8

Base deletion:

Answer 8

A base is deleted from the DNA.
This changes the sequence of codon starting from the point of deletion , thus changing the sequence of amino acid and a non-functional protein is produced.

Question 9

Examples of genetic disorders caused by gene mutation:

Answer 9

Sickle cell anaemia, albinism, haemophilia 血友病

Question 10

Explain sickle cell anaemia:
(caused by what?)
(result)
(effect)

Answer 10

It is cause by a change in the gene responsible for producing haoeglobin .
It is also due to gene mutation by base subtitution.
As a result, abnormal haemoglobin is formed.
The abnormal haemoglobin can crystallise and transport less oxygen.
In low oxygen concentration, the red blood cells are distorted to become sickle-shaped.
The individual suffers anaemia as the haemoglobin cannot transfer enough oxygen as well as weakness,aching joints and poor blood circulation.

Question 11

Explain albinism:
(changes what?)
(becomes what?)
(result)
(lack of what?)
(albinos have what?)
(skin what?)

Answer 11

Albinism is caused by a change in the gene that controls the formation of the melanin pigment.
The gene becomes defective, cannot carry out its function and is recessive.
As a result, melanin pigment cannot be produced.
There is a lack of melanin or pigmentation in the skin,hair and eyes.
Albinos will have white hair, pinkish eyes and skin.
The skin is also very sensitive to sunlight because there is a lack of melanin pigment to absorb ultraviolet rays.

Question 12

Explain haemophilia:
(caused by?)
(result)
(__bleeding and injury)

Answer 12

It is caused by a defective recessive allele on the X chromosome.
Hence, the blood clotting factor VIII cannot be synthesised, causing blood to clot very slowly.
Thus, there may be prolonged bleeding following an injury.