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How do the fossil record, homologous structures and vestigial structures
provide support for evolution? Be able to name examples of each from class.
- Fossil Record: shows structures of organisms with a time record. More similar organisms are more recent than more similar with older.
- Vestigial Structures: natural selection does not act because they have a neutral function (ex: human appendix does not affect reproduction or survival)
- Homologous Structures: different organisms have similar structures due to a common ancestor- common ancestors part of the evolution theory
What are some reasons that deleterious alleles are not lost from populations
due to adaptive evolution?
- because of heterozygote advantage- recessive allele hidden
- also because of balancing selection- least common trait is selected for
Explain why genetic drift tends to reduce genetic variability in a population over time
while gene flow tends to increase variability.
- Variability is reduced because in the bottleneck effect many individuals wiped out so traits of the population are lost and founder effect only a few individuals starting off the population so less variability
- Gene flow increases variability because members of the same species with new traits bring these traits into the population when they reproduce with the population that was there before
In a population of 1,000 individuals, would you expect genetic drift to affect allele frequencies? Why or why not?
No because they only affect small populations. 1,000 too large
Would the following statement be considered Lamarckian or Darwinian? Why? “A body-builder’s offspring are likely to be more muscular than the average person because the big muscles acquired by the body-builder are passed on to his/her offspring.”
Lamarckian because the muscles are an acquired trait- cant be passed on
For each of the following conditions that would lead to speciation, note if
the mechanism is allopatric or sympatric, prezygotic or postzygotic, and the
specific type of pre or post-zygotic isolation:
a. Two populations of stickleback fish evolve different courtship behaviors though they live in the same lake
b. Two populations of beetles are separated by a large body of water and gene flow is not observed between these population in the wild. Mating can occur between these two populations as observed in the laboratory,
but the offspring do not develop or die shortly after hatching.
A: Prezygotic barrier- behavioral isolation
B:Post zygotic barrier: reduced hybrid viability
What is microevolution?
a change in allele frequencies in a population over generations
How can evolution occur?
- Natural Selection
- Genetic Drift
- Gene Flow
Is evolution occuring if allele frequencies are changing? stay the same?
- changing? yes
- stay the same? no
What is a cline?
change in a trait you can see and measure
What is fitness?
survival in reproduction
What is average heterozygosity?
a way to measure the variation in a population. Measures the average percent of genes that are heterozygous
What is nucleotide variability?
measured by comparing the DNA sequences of pairs of individuals
What happens if a population has little variation instead of a lot?
less evolutionary potential
What generates genetic variation?
- sexual reproduction
What are mutations?
- changes in the nucleotide sequence of DNA
- cause new genes and alleles to arise
- can be benneficial or harmful
can all mutations be passed on?
no, only mutations in the cells that produce gametes
Why do mutations occur?
- mistakes during DNA replication and meiosis
- proofreader problem (some viruses)
What are types of mutations?
- point mutations: change of a single neucleotide
- Altering gene number or position: genes are duplicated (ex: our ancestor only had genes to sense some smells but they duplicated and today we can smell many different smells)
How does sexual reproduction generate genetic variation?
- sexual reproduction can shuffle existing alleles into new combinations
- recombination produces genetic differences
What is a population?
a localized group of individuals capable of interbreeding and producing fertile viable offspring
What is a gene pool?
- consists of all the alleles for all loci in a population
- a locus is fixed if all the individuals in a population are homozygous for the same allele
What is an example of a selective pressure?
What is genetic drift?
- Chance events that cause allele frequencies to fluctuate in an unpredictable way
- most common in small populations
- 2 Types: bottleneck effect and founder effect
Why is genetic drift more common in small populations?
bc random chance events affect small populations more than large ones
What is the founder effect?
- occurs when a few individuals move or become isolated from a larger population and start over as their own population
- allele frequencies in the smaller population can be different and with less variability than large pop
What is the bottleneck effect?
- a sudden reduction in pop size due to a change in the environment, usually natural disaster
- resulting gene pool may no longer have all the traits that it once did
- if the pop remains small, it may further be affected by genetic drift
example of founder effect and bottleneck?
- founder: population of finches in brazil- 3 get blosn to galapagos. Those 3 are the start of the population there
- bottleneck: natural disaster 10 mice survive, they are the gene pool
What is a deleterious allele?
and allele that causes damage
Can decrease in variability lead to less viable offspring?
yes because of inbreeding
What is gene flow
- new alleles are transferred into or out of a population by movement of fertile individuals
- ex: mating of green beetles that move into a pop of yellow beetles in a yellow environment would be worse adapted bc more green in a yellow environment- counters the effects of adaptive evolution
What is adaptive evolution?
evolution that is due to natural selection making organisms more adapted to the environment
What are the modes of selection?
- Directional selection
- Disruptive selection
- Stabilizing selection
What is directional selection?
- one of the extremes is selected for
- ex: volcano errupts and environment suddenly dark. dark mice selected for not middle or light
What is disruptive selection?
- both extremes selected for, no middle
- ex: earthquake and 2 extremes separated
What is balancing selection
middle selected for
Why is natural selection key to adaptive evolution?
because the environment can change, adaptive evolution is a continuous process
Do genetic drift and gene flow consistantly lead to adaptive evolution?
- no because adaptive evolution generates/selects traits that are favorable and gene flow and genetic drift can generate either
- genetic drift and gene flow contribute to evolution but not adaptive evolution.
What is sexual selection?
- selection of who to reproduce with based on traits
- 2 types: intersexual and intrasexual
What is intersexual selection?
- Mate choice
- The ones who have the favorable trait will be selected by the gender who selects to reproduce and pass on that trait
What is intrasexual selection?
Competition among individuals of one sex (usually male) to reproduce with mates of the opposite sex
What is sexual dimorphism?
ex: elephant seals fight for females- sexual dimorphism here because as a result of intrasexual selection has led to 30% larger males because they are winning the fights and passing on genes for largness
Why arent unfavorable alleles removed from the population?
- Diploidy (heterozygous) maintains genetic variation because the recessive allele is hidden but still there
- Balancing selection
What is balancing selection?
- occurs when natural selection maintains stable frequencies of 2 or more phenotypic forms in a population; active selection for big and little alleles
- 2 types: Heterozygote advantage and Frequency dependent selection
What is heterozygote advantage?
- The individual with both alleles bennefits most
- ex: sickle cell anemia
What is Frequency dependent solution?
- the allele that is less frequent in a population is selected for
- ex: right and left mouthed fish
- ex: flies choose the males with the less common eye color to reproduce with so when that becomes common it switches
What is neutral variation?
- genetic variation that appears to confer no selective advantage or disadvantage
- variation not positive or negative.
- ex:variation in non coding regions of DNA or variation in proteins that have little effect on protein function or reproduction
Why cant natural selection fashion perfect organisms?
- selection can only act on a trait if there is variation
- only if something already exists can it be selected for (ex: humans cant be selected to have more arms bc that trait doesnt exist)
- adaptations are compromises- ex seals often on rocks so could use legs, but dont need them bc flippers can swim and move
- Change, natural selection and the environment interact- what is benneficial is always changing and the long evolution process cant always keep up with the same speed that the environment changes at
What is reproductive isolation?
- barriers that prevent 2 species from producing viable fertile offspring
- prezygotic and postzygotic barriers
What are prezygotic barriers?
- Barriers not allowing 2 species to come together to even attempt to reproduce
- habitat isolation- organisms never cross paths
- behavioral isolation- organisms have different mating rituals and dont understand eachother
What are post zygotic barriers?
- 2 species attempt to reproduce, but there is a problem after
- Reduced hybrid viability-offspring never hatches or dies early
- Reduced hybrid fertility- offspring cant reproduce to make more
What is a hybrid?
- offspring of classes of different species
- ex: mule (infertile)= horse +donkey
What is the biological species concept?
- 2 organisms are in the same species if they can reproduce to create viable fertile offspring
- limited to sexual organisms only
- fossils and asexual (Prokaryote) organisms this rule does not apply
How can we tell if prokaryotes are related?
- morphological species concept: look for similarities in structural features
- --> works for sexual and asexual species but some similarites could be falsely seen as related when actually due to convergent evolution
- compare DNA sequences (best way)
What is convergent evolution?
- organisms are not closely related but have similar traits bc they live in similar environments
- analogous structures- structures due to convergent evolution that form because of an environment
What is the ecological species concept?
- views a species in terms of their ecological niche (2 species in same environment cannot have the same niche)
- applies to sexual and asexual populations and emphasizes the role of disruptive selection
What is the phylogenic species concept?
- defines a species as the smallest group of individuals on a phylogenic tree
- but can be difficult to determine the degree of difference required for seperate species
What is allopatric speciation?
- gene flow is interrupted or reduced population geographically separated and isolated from eachother - become sub populations
- these seperate populations may evolve independently through mutation, natural selection and genetic drift
- Reproductive isolation between pops generally increases as distance increases
- --> this is why regions with more geographic barriers have more species
What is sympatric speciation?
- takes place in geographically overlapping populations
- less common
What are the causes of sympatric speciation?
- habitat differentiation: appearence of new ecological niches (ex: some maggot flies prefer to live and eat apple trees than the others who want hawthorne trees, apple tree flies are different over time)
- Polyplody: extra sets of chromosomes due to errors in cell division
- Sexual selection:selection of mates of different colors
What holds species together?
- Gene flow
- no gene flow --> 2 seperate species
What are the longterm effects of allopatric speciation?
- geographic isolation restricts gene flow between pops
- reproductive isolation may then arise by natural selection, genetic drift, or sexual selection in the isolated populations
- eventually they are different species and can no longer interbreed
What are the effects of sympatric speciation?
- a reproductive barrier (non geographic) isolates a piece of the population in the same area as the popultion
- can result from polyploidy, habitat differentiation followed by natural selection, or sexual selection
What is the order of classification?
What are sister taxa?
share an immediate common ancestor
Why are phylogenic trees like hypotheses?
bc its not definite whos most related were still collecting evidence.