- Gene- A length of DNA which codes for the production of a polypeptide.
- Allele- One of the different forms of a gene that occupy the same locus on homologous chromosomes.
- Locus- The position of a gene on a chromosome.
- Phenotype- A person's observable characteristics.
- Genotype- The genetic make-up of a person.
- Dominant- A dominant allele always shows its effect on the phenotype.
- Recessive- A recessive allele only shows its effect on the phenotype when the dominant allele is absent.
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Phenylketonuria & Huntington's Disease
- Recessive gene mutation on chromosome 12.
- Lack of phenylalanine hydroxylase.
- Results in high levels of phenylalanine.
- Toxic to young children.
- Autosomal dominant gene mutation on chromosome 4.
- CAG codes for glutamine.
- Mutation causes a repetition of CAG so a series of them produces Huntington's proteins.
- People with Huntington's have 40 or more repeats.
- memory loss
- changes in personality & mood
- uncontrolled muscle movements
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- Recessive gene mutation on chromosome 7.
- Deletion of three base pairs results in loss of an amino acids.
- Makes the cystic fibrosis transmembrane regulator protein (CFTR).
- Blocks the movement of chloride ions and water across membranes.
- Causes the secretion of abnormally thick mucus.
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When both alleles affect the phenotype.
- Sickle cell anaemia and ABO blood groups caused by co-dominance.
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Malaria & Sickle-Cell Anaemia
In areas where malaria is endemic, sickle cell anaemia has a heterozygous advantage.
- HbA HbA
- Malaria affects the person normally
- HbA HbS
- Causes malaria infection to stay in body longer
- Immune system has longer to react
- Composition of RBC changed, parasite can't reproduce as much.
- HbS HbS
- Person has sickle cell anaemia
Causes an increase in frequency of HbA HbS.
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