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  • Created by: Megan
  • Created on: 07-03-14 14:01

DNA Mutations

Mutation - a random change to genetic material before nuclear division

Chromosome mutations - changes to parts of or to the whole chromosomse (deletion, inversion or translocation)

Somatic Mutations - mutations that occur in mitosis so are not passed on to offspring - they contribute to ageing and cancer

Point Mutations/Substitution - one base pair replaces another

Insertion/Deletion - one or more nulceotide pairs are inserted or deleted from alengt of DNA, causing a frameshift, where evrey triplet after the frst to be changed is also changed

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Mutations & Genetic Diseases

Cystic Fibrosis - 70% of cases are due to the deletion of a triplet of base pairs, deleting an amino acide fromth e 1480 in the normal sequence

Sickle-cell Anaemia - a point mutation on codon 6 for the beta polypeptide chains of hamoglobin. This cuases the amino acid valine to be inserted in place of glutamic acid

Tumours - Growth - promoting genes called protooncogenes changed into oncogenes by a point mutation which alters the ability of the protooncogenes to be switched off. THe oncogenes promtoes unregulated cell division, creating a tumour

Huntington's Disease - results from an expanded triplet nucleotide repeat or a stutter. The normal gene has repeating CAG sequences and if these expand above a threshold number, the protein is altered enough to cause Huntington's Disease

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Neutral Effects

An allele is an alternative version of a gene with the same locus on the chromosome and codes for the same polypeptide but the alteration to the DNA base sequence may alter the protein's structure

An allele ma produce no change to the organism if:

  • the mutation is in a non coding region of DNA
  • it is a silent mutation - although the base triplet has changed, it still codes for the same amino acid so the protein is unchanged
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Harmful and Beneficial Effects

Early humans is Africa almost certainly had dark skin. Melanin protected them from the harmful effects of UV light yet could still synthesise vitamin D from the action o fthe inense sunlight on their skin - this is an importnant source of Vitamin D as we eat food that contains very little Vitamin D.

  • Humans with mutations of the genes determining skin colour, producing paler skin, would have burned and suffered from skin cancer

As human migrated to more temperate climes, the sunlight was not intense enough to cause Vitamin D to be made by those with darker skins. Humans with mutations producing paler skin or lack of pigmenwould have an advantage over those with darker skin as they could synthesise more vitamin D.

  • Lack of vitamin D = rickets and a narrow pelvis, producing difficulties in childbirth Vitamin D helps protect against cancer and heart disease

The inuit people have not lost all their skin pigments, although they do not live in an environment that has intense sunlight because they eat a lot of fish and seal meat, both rich sources of dietary Vitamin D

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