microevolution

darwins two major points

1. common ancestry: organisms on the earth today descended from ancestral species

2. natural selection: a population of organisms can change over generations if individuals having certain heritable traits leave more offspring than others

what is the result of darwins points?

adaptations: an accumulation of inherited characteristics that enhance an organism’s ability to survive and reproduce in specific environments

evolution

genetic composition of a population changing over time

common ancestry

• all organisms are related, descended from a common ancestor

• as descendants moved into various habitats, they accumulated diverse adaptations that fit their specific ways of life

natural selection

• differential success of reproduction

• occurs through an interaction between the environment and the variation in a population

• the product of natural selection is the adaptation of a population to its environment

how does natural selection occur?

1. all organisms tend to over reproduce

2. environmental factors screen the populations traits, favoring some over others

3. different reproductive success: organisms with favorable traits produce more offspring than those without the traits

4. the favoured trait dominates the next generation

artificial selection

selective breeding of domesticated animals and plants

what evidence is there to support evolution?

• direct observation of evolutionary change

• homology

• fossil record

• biogeography

• math

direct observation of evolutionary change

• insecticide resistance: DDT

• antibiotic resistance

• HIV drug resistance

• response to changing food sources

homology

similarity in characteristics resulting from common ancestry

what are the three types of homology?

1. anatomical homology

2. embryological homology

3. molecular homology

anatomical homology

animals grouped into the same taxonomic level share similar structures

embryological homology

similarities in the embryological development of closely related organisms that will develop into homologous structures

molecular homology

all living things have dna and rna, by comparing the proteins of organisms, we can predict how similar the dna is and how closely related the organisms are

homologous structures

structures with underlying similarities even though they are adapted for different functions

• created by divergent evolution

vestigial organs

structures of little importance to an animals survival

• appendix

convergent evolution

the independent evolution in different lineages due to similar selection pressure → analogous structures

fossil record

natural history of life on earth

how do we date fossils?

• the age of rocks where the fossil was found

• the rate of decay of isotopes including carbon 14

• geographical data

biogeography

scientific study of the geographic distribution of species

• species are more closely related to other species from the same area

endemic species

islands have many endemic species

• species found nowhere else in the world

microevolution

change in the genetic makeup of a population from generation to generation

• individual organisms don’t evolve, populations do

• the characteristics of an individual affect its chances of survival and reproductive success

• in an evolving population, some characteristics become more common while others decline

species

group of organisms that can breed and produce fertile offspring

population

group of individuals in an area belonging to the same species

gene pool

all alleles at all gene loci in all individuals of the population → all alleles available to a population

alleles

alt version of a gene, may be dominant/recessive

genotypes

the genetic makeup of a trait

homozygous

having two identical alleles for a given gene

heterozygous

having two different alleles for a given genes

phenotype

the physical appearance of a trait

allele frequency

number of times that allele occurs in the population/total number of alleles in the population

discrete characters

classified on an either or basis; usually controlled by a single gene

quantitative characters

characters that vary along a continuum; usually controlled by two or more genes

average heterozygosity

the average % of loci that are heterozygous

what are sources of genetic variation?

variation originates when mutation, gene duplication, or other processes produce new alleles and new genes

• new alleles can arise from a mutation

rapid reproduction

even though mutation rates are low in prokaryotic cells (less than 1 in 100,000 genes) their short generation spans allow mutations to quickly generate genetic variation

hardy weinberg equation (genotypic frequency)

p² + 2pq + q² = 1

allele frequency equation

p + q = 1

what are the variables for calculating the hardy weinberg equation?

p = frequency of the dominant allele

q = frequency of the recessive allele

what are the three major factors that alter allele frequencies and cause most evolutionary change?

1. natural selection

2. genetic drift

3. gene flow

natural selection - altering a population’s genetic composition

differential reproductive success will increase the frequency of some alleles while decreasing others

genetic drift - altering a population’s genetic composition

• change in allele frequency simply due to chance

• reduces variation in a population through loss of alleles

• small populations are more likely to feel the effects of genetic drift

what are the two situations that increase the likelihood of genetic drift occuring?

1. bottleneck effect

2. founder effect

3. gene flow

bottleneck effect

occurs when a populations numbers have been greatly reduced by a random event; the new population doesnt have allele frequencies that reflect the original population

founder effect

occurs when a few individuals become separated from a larger population and establish a new population; this new population will not have allele frequencies that reflect the original population

what are the effects of genetic drift?

• genetic drift is significant in small populations

• genetic drift can cause allele frequencies to change at random

• genetic drift can lead to a loss of genetic variation within populations

• genetic drift can cause harmful alleles to become fixed

gene flow

• migration of fertile individuals between populations

• a population may gain or lose alleles this way

• reduces differences between populations

natural selection - adaptive evolution

• favours some alleles over others → natural selection not random

• natural selection consistently increases the frequencies of alleles that provide a reproductive advantage → adaptive evolution

relative fitness

the contribution an individual makes to the gene pool of the next generation relative to the contributions of other individuals

balancing selection

when natural selection maintains stable numbers of two or more phenotypes in a population by preserving variation at some loci

• heterozygote advantage

• frequency dependent selection

heterozygote advantage

individuals that are heterozygous at a particular locus have greater fitness than the individuals that are homozygous

frequency dependent selection

when the fitness of an organism depends on how common it is in the population

sexual selection

individuals with certain inherited characteristics are more likely than other individuals of the same sex to obtain mates

• results in sexual dimorphism: a difference in secondary sex characteristics between males and females of the same species

intrasexual selection

selection within the same sex

intersexual selection

individuals of one sex are choosy when selecting their mates