GENETIC MUTATION 4X EXAMPLES Flashcards
The TYR GENE, tyrosinase and albinism
Describe albinism
Reference melanin and symptoms
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.
Where is the TYR gene found
Long arm of chromosome 11
What type of allele results in albinism
A faulty recessive one
Melanin metabolic pathway production
Tyrosine —> DOPA by tryosinase —> dopaquinone —> melanin
How the metabolic pathway is disrupted and albinism occurs
The recessive allele of the gene for the enzyme tryosinase results in absence or inactive presence.
Tyrosine (amino acid) cannot be converted to melanin.
THE HBB GENE, haemoglobin and sickle cell anaemia
What does HBB code for
The amino acid sequence in B-globin polypeptide in haemoglobin
Where is HBB found
Short arm of chromosome 11
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
DNA = CTC —> CAC
mRNA = GCG —> GUG
Amino acid = Glutamic acid —> Valine
How does this affect haemoglobin and oxygen
What can it lead to
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.
What does a person with a normal HBB gene and a mutated one have
They make normal haemoglobin and sickle haemoglobin. They generally show no symptoms.
Symptoms of sickle cell
Fatigue
Weakness
Pale or yellowish skin
Where is the sickle cell trait more common and why
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.
THE HTT GENE, Huntington and huntingtin disease
Where is the HTT gene found
Locus on chromosome 4
What does HTT code for and why is that important
Codes for the production of huntingtin protein.
Important in the development of neurone particularly in the brain.
How the mutation occurs HTT
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.
When do symptoms show and what are they
HTT
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.
What is the allele like for HTT?
What does this mean about the chances of inheriting?
Faulty dominant allele
1 in 2 chances that a person with a parent with the allele will inherit the condition
THE F8 GENE, factor VIII and haemophilia
What does F8 code for
The protein called coagulation factor VIII
Where is factor VIII synthesised and moved to
What does it do
Synthesised in the liver cells and is secreted into the blood plasma to help blood clot.
Where is F8 found
What does this mean
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
How does haemophilia this occur?
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
How many normal genes are needed to make enough factor VIII
1
THE Le GENE, gibberellin and stem elongation
What are the dominant and recessive Le genes
Le = grown tall
le = shorter
What does the dominant Le gene regulate
the synthesis of the last enzyme in a pathway that produced an active form of giberellin, GA1 which stimulates cell elongation and growth.
What changes cause this to occur?
Le Gene
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.
What does it mean if a plant is lele homozygous
It is genetically dwarf
