BIOL 111 - Midterm #1 Flashcards
What are the three conditions for evolution by natural selection?
Variation in traits (phenotypic variation)
Differential reproduction of variants (Fitness differences)
Heredity - Higher fitness individuals have offspring with the higher fitness traits.
What is the end result of evolution by natural selection?
A population in which more individuals are adapted to the environment.
What is evolution?
A change in the frequency of alleles in a population.
What is selection?
Differential reproduction of phenotypic variants in a population.
Can selection occur without leading to evolution?
Yes, if the phenotypic variation does not have a genetic basis.
Ex: A population becomes smaller due to a lack of food.
Can evolution occur without selection?
Yes, allele frequencies can change for other reasons.
However, only selection leads consistently to higher fitness.
What cause(s) of evolution are non-random?
Selection
What causes of evolution are random?
Genetic drift, gene flow, and mutation.
What must be present before evolution by selection can occur?
Genetic variation.
What is fitness?
Reproductive success.
Individuals with higher fitness contribute more alleles to the gene pool of the next generation.
What three things did Darwin explain in On the Origin of Species?
How evolution by natural selection works.
Provided evidence that evolution by natural selection was common.
Provided evidence that evolution has occurred.
What has lead to the diversity of life today?
Repeated speciation
What is speciation and how does it occur (broad)?
Speciation is how a new kind of plant or animal species is created. Speciation occurs when a group within a species separates from other members of its species and develops its own unique characteristics.
What are homologous characters?
Characteristics that have been inherited from a common ancestor.
Ex: Arm structure in humans, cats, whales and bats.
Humerus -> Radius & Ulna -> Carpals -> Metacarpals -> Phalanges.
Where might you see homologous characters?
Some homologous characters can be seen in embryos but not in adults.
Extinction and replacement
Old species go extinct and are replaced by new species.
Geologic succession
Older species are very different from modern ones, more recent species are more similar to living species.
Where might endemic species be found?
Islands often have unique endemic species that are related to species on the nearest mainland.
How can a population be defined?
A population is a subset of individuals of one species that lives in a certain geographic are and interbreeds.
What is a gene pool?
All of the alleles of every gene in a population
What is allele frequency?
The relative proportion of an allele of a particular gene.
Ranges from 0 to 1.
When would you say an allele is fixed?
When the allele frequency is 1 and thus there is no variation.
What is genotype frequency?
The relative proportion of a genotype of a particular gene.
If there was 3 brown and 1 green beetle the genotype frequency of the brown genotype would be 0.75.
What is micro evolution?
Any change in the allele frequency in a population.
What are the four processes that cause micro evolution?
Selection
Genetic drift
Gene flow
Mutation
What is a potential cause in an increase in allele frequency?
If the allele leads to higher reproductive success or fitness.
What is directional selection?
A shift in the overall makeup of a population by favouring variants that are at one extreme of the distribution.
If dark mice blend in best the makeup of the population will shift to be darker as opposed to lighter.
What is disruptive selection?
Disruptive selection favours variants at both ends of the distribution.
Dark and light mice survive the best compared to a neutral colour even though they are on opposite sides of the distribution.
What is stabilizing selection?
Extreme variants are removed from the population and preserves intermediate types.
Dark mice and light mice are easily spotted whereas neutral coloured mice blend in best and survive.
What does selection typically do to the amount of genetic variation in a population?
Decreases the genetic variation as alleles that are unfavourable are deleted leaving the alleles that lead to higher fitness.
What are two examples of selection maintaining variation?
In areas with malaria people who are heterozygous for sickle cell anemia have higher fitness so variation is maintained.
Frequency-dependent selection - The fitness of a phenotype depends on its frequency in the population.
When population of left-mouthed fish is higher than right mouth, right mouth fish have higher fitness.
What is sexual selection?
Selection due to characters that affect mating success.
Can often favour traits that reduce survival - brightly coloured animals are preferred by mates but easier for predators to spot.
What are the two main forms of sexual selection?
Intersexual - Females choose males with the best display.
Intrasexual - Combat between males for female partners.
Why are females the ones who typically select a mate?
Females have a higher cost of reproduction and have a lower reproductive potential over their lifetime.
What is genetic drift?
Random change in allele frequency.
What is the founder effect?
The founder effect is when a small number of individuals colonize a new area.
The new area is not representative of the old areas allele frequency.
What size of population does drift impact the most?
Drift impacts smaller populations the most.
Larger samples are more likely to be representative of the allele frequency in the population.
In very small populations alleles drift rapidly to fixation or extinction.
What is gene flow?
Movement of alleles between populations due to migration of individuals.
Ex: Brown beetles from the desert move to forest and increase the frequency of brown allele among the green beetle population.
What is the ultimate source of genetic variation?
Mutation
What is a mutation?
A change in the DNA sequence.
Where in the genome can mutations occur?
Anywhere
What are some causes of mutation?
DNA damage that is not accurately repaired
Replication errors
Viruses
Transposable elements
Why do most mutations reduce or not change fitness?
Populations are already adapted to their environment so a mutation that increases fitness is rare.
What is the difference between populations and species?
A species is a group of populations whose members can interbreed.
Populations belong to different species when there is enough genetic difference to inhibit gene flow.
What is a prezygotic barrier and what are some example?
Prezygotic barriers occur before birth and hinder mating.
Temporal isolation - Members of the same species reproduce at different times.
Habitat isolation - Habitats occupied by species differs
Mechanical isolation - Some members physically can not mate with each other.
Behavioural isolation - Individuals have different mating practices.
What are postzygotic barriers?
Postzygotic barriers prevent a hybrid zygote from being a viable/fertile adult.
-Reduced hybrid viability
-Reduced hybrid fertility
-Hybrid breakdown
What is speciation?
The evolution of a new species from an old species on the basis of genetic divergence.
What microevolutionary processes promote speciation?
-Mutation
-Genetic drift
-Selection
What mode of speciation has an initial barrier to gene flow involving geographic isolation?
Allopatric isolation.
How does allopatric isolation occur?
Dispersal - A population disperses to and becomes established in a new area.
Vicariance - A barrier is formed between two populations.
Ex: Snapping shrimp on either side of the Isthmus of panama.
Why has allopatric speciation produced many pairs of western and eastern species?
During the ice ages northern species migrated south to ice-free areas, some going east some west.
What can maintain reproductive isolation between reproductive species?
Sexual selection - females sexually select males of a certain physical appearance even if hybrids are viable.
What is allopolyploidy?
Multiplication of chromosome sets through hybridization.
What is polyploidy and where does it often occur?
Polyploidy refers to having more than two sets of chromosomes and is common in plants.
Two sympatric species having different chromosome numbers or morphologies form a hybrid, and that hybrid produces offspring with a doubled number of chromosomes
What is allopolyploidy?
Multiplication of chromosome sets through hybridization.
What are hybrid zones?
Hybrid zones are where the habitats of two or more species meet and overlap. If the species diverged recently they may still produce viable offspring.
What are the three posible results of the formation of a hybrid zone?
Reinforcement - Reproductive barriers strengthen resulting in hybrids ceasing to be created.
Fusion - Reproductive barriers weaken, fusing the two species.
Stability - Continued production of hybrid individuals as well as individuals from the original populations.
What is introgression?
The incorporation of alleles from one species into the gene pool of the other species through hybridization.
Summarize speciation
A barrier to gene flow isolates two populations.
The populations evolve genetic differences through selection, genetic drift and mutation.
The populations have evolved into different species.
What does each node (branch point) represent in a phylogenetic tree?
A common ancestor
What is phylogeny?
Phylogeny refers to the evolutionary history of a group of organisms
What are sister taxa?
Sister taxa are a group of organisms that share a unique common ancestor not shared with any other taxa.
Glass lizards + monitor lizards are sister taxa.
(Glass lizards + monitor lizards) + Iguanas are sister taxa.
What is the role of an out group in a phylogenetic tree?
The out group allows us to infer the ancestral state for each character. Outgroup is a species that diverged from all in group taxa before they diverged from each other. Proffered way to determine the root of a phylogenetic tree.
What are analogous characters?
Analogous characters are characters that function and appear similar but are not inherited from the same common ancestor.
The result of convergent evolution.
Different structures with similar functions - birds with wings vs insect wings.
Where can homologies be detected?
They can be detected in macro molecular sequences.
At what rate do neutral mutations accumulate?
A constant rate.
Genes for seven proteins in mammals accumulated 30 mutations every 45 million years.
What are some limitations of molecular clocks?
Must be calibrated using an independent estimate of time since divergence.
Different genome pars evolve at diff rates
Same genes may evolve at different rates in different lineages.
What is a monophyletic group(Claude)?
A group that consists of an ancestral species and ALL its descendants.
What is a paraphyletic group?
A group that consists of an ancestral species and some but not all its descendants.
What is a polyphyletic group?
A group that does not include the most recent common ancestor of the group.
What is a crown group?
Living descendants of a common ancestor.
What is a stem group?
An extinct taxa more closely related to the crown group than any other living taxa.
