How can populations evolve to form new species or to eliminate a species?

What causes a population’s gene pool to change?

Evolution Karen A. Robinson

Evolution Topics Covered: Genes and evolution Genes and evolution Changes in a population’s gene pool Changes in a population’s gene pool Formation of new species Formation of new species Genes tell evolutionary history Genes tell evolutionary history

What is evolution Evolution is defined as a change in the frequency of alleles in a population over time. Evolution is defined as a change in the frequency of alleles in a population over time.

I.Genes and Evolution Heredity is controlled by genes Heredity is controlled by genes Genes are carried on the chromosomes Genes are carried on the chromosomes Changes in genes or chromosomes create variation Changes in genes or chromosomes create variation Genetic variation is the cause for evolution Genetic variation is the cause for evolution Evidence shows how evolution occurs Evidence shows how evolution occurs Evidence shows why evolution occurs Evidence shows why evolution occurs

II.Populations and Gene Pools Genetic variation and evolution studied Genetic variation and evolution studied Population: a group of species that interbreed Population: a group of species that interbreed Interbreeding produces a common gene pool Interbreeding produces a common gene pool Genes can have different alleles or versions of that gene Genes can have different alleles or versions of that gene Dominant and recessive alleles Dominant and recessive alleles Allelic frequency is studied Allelic frequency is studied

Evolution and Allelic Frequency Evolution has occurred if change in allelic frequency occurs. Evolution has occurred if change in allelic frequency occurs. Example- population contains: Example- population contains: 48% heterozygous black mice Bb 48% heterozygous black mice Bb 36% homozygous brown mice bb 36% homozygous brown mice bb 16% homozygous black mice BB 16% homozygous black mice BB B is the dominant allele (black) and is shown more frequently (36% + 16%= 52%) B is the dominant allele (black) and is shown more frequently (36% + 16%= 52%) If the B allele drops to 30%, the population is evolving. If the B allele drops to 30%, the population is evolving.

How can we predict evolution will occur? Hardy-Weinberg Principle states: Hardy-Weinberg Principle states: Allele frequencies in a population should remain constant Allele frequencies in a population should remain constant Factors cause those frequencies to change Factors cause those frequencies to change Makes predictions for populations Makes predictions for populations p squared + 2pq + q squared=1 p squared + 2pq + q squared=1 Ex: p is dominant and q is recessive Ex: p is dominant and q is recessive will give more information regarding the Hardy-Weinberg Principle will give more information regarding the Hardy-Weinberg Principle

III. Formation of a New Species Speciation: formation of a new species Speciation: formation of a new species Typically speciation is due to reproductive isolation Typically speciation is due to reproductive isolation

Reproductive Isolation Population will evolve into two separate species Population will evolve into two separate species Due to: Due to: Behavioral Isolation Ex: differences in mating rituals Behavioral Isolation Ex: differences in mating rituals Geographic Isolation: two populations separated by geographic barriers Geographic Isolation: two populations separated by geographic barriers Temporal Isolation: Two or more species reproduce at different times Temporal Isolation: Two or more species reproduce at different times

Evolution in a Nutshell Evolution is a continuous process Evolution is a continuous process Evolutions is evident through fossil records Evolutions is evident through fossil records Evolution can be calculated using the Hardy- Weinberg Principle Evolution can be calculated using the Hardy- Weinberg Principle Evolution is typically caused by environmental factors Evolution is typically caused by environmental factors choose evolution for information regarding evolution choose evolution for information regarding evolution

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