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Evolution: is the charge over time in the proportion of individual in population differing in one or more inherited traits

it can occur through processes :

random e.g. genetic drift

non-random e.g. nature and sexual election

Mutations:

variation is a result of mutations

it is the the original source of new alleles

mutation is a change in the genetic composition of a cell

and is divided into two main groups:

gene mutations

chromosomal mutations

mutations have low frequency and occur randomly

Frequency of mutations:

-environmental factors can increase the frequency of mutations. these factors are known as ----> mutagens agents/mutagens.

mutagens can be classed as:

physical: mechanical damage to DNA, ionising radiation ,high temperature

chemical - alter or remove base.

enzymatic: free radicals, mistakes in DNA replication, mistakes in recombination and repair

occurrence of mutation:

DNA replicating machinery makes mistakes that go uncorrected .

Bases shift to alternative tautomeric form that paris incorrectly.

too many or too few bases inserted.

bases may de-aminate, altering base pairing.

Gene Mutations:

Germline mutation: affects gametes and so can be transmitted to the next generation.

Somatic Mutation: affect the somatic cells.

morphological mutation: causes visible change in an affected organism.

nutritional mutation: renders organism dependent on added nutrient.

Lethal mutation: occurs in indispensable genes.

conditional mutation: affects mutant organism only under certain circumstances.

silent mutation: affects genotype but not phenotype.

reversion:

occur in two ways:

mutated base changes back to its original identity(true reversion)

Another change can occur that compensates fior the mutation.

TYPES OF MUTAIONS 1 :

insertion: an additional base is inserted

deletion: base is deleted

insertions and deletion affect the codons following the mutation and therefore the reading frame

substitution: a base is substituted for another <-- affect one codon and do not change the reading frame.

TYPES OF POINT MUTATION:

silent: has no effect on the protein sequence.

missense: results in an amino acid substitution.

sense: substitutes a stop codon for an amino acid.

FRAME SHIFT:

insertion or deletion nucleotides may result in a shift in the reading frame or insertion of a stop codon.

SELECTION:

can be:

density-dependent

density independent

density-dependent pressures are affected by population size. e.g

-avaliability of resources- food, water etc.

-biological factors , predators , disease

density independent:

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