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Genetic Diversity and Adaptation (Gene Mutation (Base substitution is when…
Genetic Diversity and Adaptation
Gene Mutation
A mutation is a change in the base sequence of DNA
Base substitution is when a DNA nucleotide is replaced by another nucleotide with a different base
This may have no impact due to the degenerate nature of genetic code
A different amino acid is coded for, which impacts the primary, secondary, tertiary and quaternary structures of the protein
Base deletion is when a DNA nucleotide is removed from the original DNA sequence
This causes a frame shift, which alters the amino acids coded for due to the non-overlapping qualities of genetic code
Base insertion is when a DNA nucleotide is added to the original sequence
This causes a frame shift, which alters the amino acids coded for due to the non-overlapping qualities of genetic code
A nonsense mutation is one which causes the introduction of a stop codon
A missense mutation is one which introduces a different amino acid
Changes in whole sets of chromosomes occur when organisms have 3 or more sets of chromosomes (polyploidy)
Non-disjunction is when homologous chromosomes fail to separate during meiosis, causing offspring to have more or fewer chromosomes in their body cells
eg. Down's Syndrome
Meiosis & Genetic Variation
Meiosis produces 4 diploid daughter cells (gametes) which are used in sexual reproduction
Meiosis is important because it maintains a constant number of chromosomes between generations, as when haploid gametes fuse, the normal number of chromosomes is restored
Genetic Diversity and Adaptation
Types of Selection
Selection is the process by which organisms which are better adapted survive and breed, and those which are less well adapted do not.
Stabilising selection is when the phenotypic average is favoured over phenotypic extremes
This occurs most when environmental conditions are stable
Eg. in baby birth weights, the mean is favoured, as being too light infant mortality is high, and when babies are too heavy there may be birth complications
Directional selection is when the phenotypic extremes are favoured over the mean
This mostly occurs when environmental conditions change, as the best suited phenotypes to the new conditions are more likely to survive and breed
Eg. antibiotic resistance