Variation and mutation

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About 104 to 105 base pairs

So, about one mutation per replication!

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HIV-AIDS Video

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Rates of mutation

Rates of mutation generally high

Leads to a high load of deleterious (harmful) mutations

Sex may be a way to eliminate or reduce the load of deleterious mutations!

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Types of mutations

Point mutations

Base-pair substitutions

Caused by chance errors during synthesis or repair of DNA

Leads to new alleles (may or may not change phenotypes)

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Types of mutations

Gene duplication

Result of unequal crossing over during meiosis

Leads to redundant genes

Which may mutate freely

And may thus gain new functions

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Types of mutations

Chromosome duplication

Caused by errors in meiosis (mitosis in plants)

Common in plants

Leads to polyploidy

Can lead to new species of plants

Due to inability to interbreed

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Effects of mutations

Relatively speaking…

Most mutations have little effect

Many are actually harmful

Few are beneficial

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How can mutations lead to big changes?

Accumulation of many small mutations, each with a small effect

Accumulation of several small mutations, each with a large effect

One large mutation with a large effect

Mutation in a regulatory sequence (affects regulation of development)

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Normal fly head

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Antennapedia fly

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Random mating

Under random mating, the chance of any individual in a population mating is exactly the same as for any other individual in the population

Generally, hard to find in nature

But, can approximate in many large populations over short periods of time

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Non-random mating

Violations of random mating lead to changes in genotypic frequencies, not allele frequencies

But, can lead to changes in effective population size…

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