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Evolution BIO Chapter 16 Cheat Sheet by

Genetic Variation

- two main sources of genetic variation: mutations & gene shuffling that results from sexual reprod­uction
- in population -> indivi­duals interbreed -> common group of genes (gene pool)
- gene pool: all different genes & alleles in a population
- relative frequency: number of times the allele occurs in a gene pool compared to number of times other alleles for the same gene occur
- evolution is any change in the relative freequency of a population

Sources of Genetic

- sexual reprod­uction does not hcange relative frequency

Single­-Gene & Polygenic Traits

- numbe of phenotypes produced for a trait depends on how many genes control the trait
- single gene trait: trait conrolled by single gene with two alleles (widow's peak) -> bar graph
- polygenic trait: many traits controlled by two or more genes (height) -> bell-s­haped curve

Natural Selection on Single­-Gene Traits

- natural selection on single­-gene traits -> changes in allele freque­ncies -> evolution

Natural Selection on Polygenic Traits

- natural selection can affect the distri­bution of phenotypes in three ways: direct­ional selection, stabil­izing selection, or disruptive selection
- direct­ional selection: indivi­duals at one end of curve have a higher fitness than middle or other end
- stabal­izing selection: indivi­duals near center of curve have higher fitness than eithe sides of curve
- disruptive selection: indivi­duals at upper & lower ends of curve have higher fitness than indivi­duals near the middle

Genetic Drift

- genetic drift: random change in allele frequency
- genetic drift can occur when a small group of a population colonizes a new habitat
- founder effect: allele freque­ncies change as a result of the migration of a small subgroup of a population

Hardy-­Wei­nberg & Genetic Equill­ibrium

- Hardy-­Wei­nberg Principle: allele freque­ncies in a population will remain constant unless one or more factors cause those freqeu­ncies to change
- genetic equili­brium: freque­ncies remain constant
- five conditions to manatin genetic eq. -> random mating, large pop, no movement in/our of pop, no mutations, no natural selection


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