GENETIC MUTATION 4X EXAMPLES

Question 1

The TYR GENE, tyrosinase and albinism

Question 2

Describe albinism
Reference melanin and symptoms

Answer 2

The relationship between gene, enzyme and human phenotype

The dark pigment melanin is partially missing from the eyes, skin and hair

In humans this results in pale blue or pink irises, very pale skin and hair.
The eye colour is accompanied by poor vision and rapid or jerky movement of the eyes.

Question 3

Where is the TYR gene found

Answer 3

Long arm of chromosome 11

Question 4

What type of allele results in albinism

Answer 4

A faulty recessive one

Question 5

Melanin metabolic pathway production

Answer 5

Tyrosine —> DOPA by tryosinase —> dopaquinone —> melanin

Question 6

How the metabolic pathway is disrupted and albinism occurs

Answer 6

The recessive allele of the gene for the enzyme tryosinase results in absence or inactive presence.
Tyrosine (amino acid) cannot be converted to melanin.

Question 7

THE HBB GENE, haemoglobin and sickle cell anaemia

Question 8

What does HBB code for

Answer 8

The amino acid sequence in B-globin polypeptide in haemoglobin

Question 9

Where is HBB found

Answer 9

Short arm of chromosome 11

Question 10

How does the DNA sequence change for people with an abnormal form of the allele
How does the mRNA sequence change
What amino acid is changed

Answer 10

DNA = CTC —> CAC
mRNA = GCG —> GUG
Amino acid = Glutamic acid —> Valine

Question 11

How does this affect haemoglobin and oxygen
What can it lead to

Answer 11

When combined to oxygen there is a difference to the molecule

When not combined the mutated b-globin polypeptide makes the haemoglobin molecule much less soluble.
The molecules stick to each other, forming long fibres inside red blood cells.
The red cells are pulled out of have into a half-moon or sickle shape.
The distorted cells become useless at transporting oxygen and get stick in small capillaries, stopping unaffected cells from getting through.
Causes anaemia (lack of oxygen transported to the cells) and may die.

Question 12

What does a person with a normal HBB gene and a mutated one have

Answer 12

They make normal haemoglobin and sickle haemoglobin. They generally show no symptoms.

Question 13

Symptoms of sickle cell

Answer 13

Fatigue
Weakness
Pale or yellowish skin

Question 14

Where is the sickle cell trait more common and why

Answer 14

More prevalent in people who are of African-descent.
HbS carriers have been naturally selected as sickle cell anaemia is advantageous through offering resistance against malaria.

Question 15

THE HTT GENE, Huntington and huntingtin disease

Question 16

Where is the HTT gene found

Answer 16

Locus on chromosome 4

Question 17

What does HTT code for and why is that important

Answer 17

Codes for the production of huntingtin protein.

Important in the development of neurone particularly in the brain.

Question 18

How the mutation occurs HTT

Answer 18

If the nucleotide sequence of this green contains over 40 recreated CAG then neurone development is abnormal and the disease occurs.
(Repetition is called a stutter)

If repeats are between 36-39 the disease may or may not develop.

Question 19

When do symptoms show and what are they
HTT

Answer 19

Condition develops as the person ages.
Often no symptoms till 30-40 so people have children who may have the disease passed on before knowing they have it.

Begin to lose the ability to control movements and to walk, talk or think clearly.
Is fatal with death occurring within 15-20 years after symptoms first appear.

Question 20

What is the allele like for HTT?
What does this mean about the chances of inheriting?

Answer 20

Faulty dominant allele
1 in 2 chances that a person with a parent with the allele will inherit the condition

Question 21

THE F8 GENE, factor VIII and haemophilia

Question 22

What does F8 code for

Answer 22

The protein called coagulation factor VIII

Question 23

Where is factor VIII synthesised and moved to
What does it do

Answer 23

Synthesised in the liver cells and is secreted into the blood plasma to help blood clot.

Question 24

Where is F8 found
What does this mean

Answer 24

On a non-homologous region of the X chromosome.

Means it is sex linked

Males cannot mask the effect of the fault allele with a normal one where as females can be heterozygous and not show symptoms

Question 25

How does haemophilia this occur?

Answer 25

Abnormal alleles of this gene result in the production less or no factor VIII. Meaning that blood does not clot normally and excessive bleeding can occur - haemophilia

Question 26

How many normal genes are needed to make enough factor VIII

Answer 26

1

Question 27

THE Le GENE, gibberellin and stem elongation

Question 28

What are the dominant and recessive Le genes

Answer 28

Le = grown tall
le = shorter

Question 29

What does the dominant Le gene regulate

Answer 29

the synthesis of the last enzyme in a pathway that produced an active form of giberellin, GA1 which stimulates cell elongation and growth.

Question 30

What changes cause this to occur?
Le Gene

Answer 30

A recessive allele of this gene has one nucleotide that differed. This allele codes for alanine instead of threonine at one position in the primary structure of the enzyme near its active site, producing a non-functional enzyme.

Question 31

What does it mean if a plant is lele homozygous

Answer 31

It is genetically dwarf