Specific Mutations

Biology: Cambridge International A Level, topic 16.2.7

There are some specific mutations you need to know for the exam:

Albinism is a recessive condition where individuals are unable to produce the pigment melanin.
This is due to mutations in the TYR gene. The TYR gene codes for a tyrosinase enzyme.
Tyrosinase is responsible for catalysing the production of melanin in pigment-producing cells called melanocytes.
Melanin is the pigment which gives skin, hair, and the iris of the eye colour.
Individuals with albinism have light-coloured skin & hair. They may also have vision problems due to melanin's role in the eye.

Sickle cell anaemia is a recessive condition where individuals have sickle-shaped red blood cells.
It is caused by a mutation in the gene which codes for the beta chain of haemoglobin. It is a missense mutation.
The change of shape to sickled means that red blood cells are able to carry less oxygen.
Individuals with sickle-celled anaemia can suffer from anaemia, pain, and increased risks of stroke.

Haemophilia is an X-linked recessive condition in which individuals blood does not colour correctly.
Individuals with haemophilia have difficulty clotting blood. This means they bleed for longer than they should. This can be a problem following trauma.
Blood clotting is controlled by multiple factors. Haemophilia results due to mutations in clotting factor VIII or IX.
The genes for these factors are located on the X-chromosome. So, we say this condition is "X-linked".

Huntingdon's disease is a dominant condition due to a mutation in the HTT gene. The HTT codes dor the huntingtin protein.
Mutations in the huntingtin protein cause premature degeneration of brain nerve cells. This degeneration leads to a variety of symptoms:
In the early stages of the disease, individuals develop jerky, uncontrollable movements called chorea.
Neuropsychiatric symptoms such as anxiety, depression, and irritability.
Cognitive abilities such as planning are also impacted.

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