Science - Mutations
DNA
- DNA stands for DeoxyriboNucleic Acid
- DNA has the shape of a double helix (like a twisted ladder)
- The DNA molecule is made up of repeating components called NUCLEOTIDES
- Nucleotides consist of three components:
- A Sugar
- A Phosphate
- One of 4 Nitrogenous Bases:
- Adenine (A)
- Thymine (T)
- Guanine (G)
- Cytosine (C)
- NOTE: You only need to know the letters, not the full names
- Adenine can only pair with Thymine, while Guanine can only pair with Cytosine
- Nitrogenous bases pair through Hydrogen bonds
- DNA contains all the instructions to create an organism
- Key term: POLYPEPTIDE, also known as a protein
- DNA is read in groups of three, called a CODON or a triplet
Mutations
- A MUTATION is the alteration of the nucleotide sequence in the genome of an organism
- A MUTAGEN is a physical or chemical agent that changes the genetic material of an organism, increasing the frequency of mutations in an organism
- Most mutations are harmless (NEUTRAL)
- Mutations that improve survivability are called BENEFICIAL mutations
- Mutations that decrease survivability are called DETRIMENTAL mutations
Examples of mutations
Beneficial:
- Name: CCR-5 HIV Immunity
- How does it occur?: Homozygous allele Δ32 (Delta-32) at the CCR-5 gene locus
- The CCR-5 gene has the Δ32 allele on both chromosomes. Δ32 is a RECESSIVE gene.
- What is the benefit?: People with this mutation are completely immune to HIV.
Detrimental:
- Name: Sickle Cell Anaemia
- How does it occur?: recessive allele in the Beta Globin gene
- The Beta Globin gene has the recessive allele on both chromosomes.
- What is the detriment?: Sickle Cell Anaemia causes the hemoglobin protein, which carries oxygen in red blood cells, to be malformed. This means that the red blood cell has a significantly lower oxygen capacity, resulting in lack of oxygen to muscles and organs. This also results in the blood cells taking on a sickle shape rather than the normal torus (doughnut) shape. However, Sickle Cell Anaemia provides immunity to malaria, which may explain why it is quite common in Sub-Saharan Africa.
