Midterm 2 Flashcards
Define character
An observable, physical, heritable factor that varies among individuals (hair color, height)
Define trait
The alternative forms of a character (brown/black hair)
Define true-breeding
Organisms that “breed true” with respect to a particular trait - breeding within only gives rise to offspring with that trait.
*Self-pollination would produce progeny that all have the same phenotype as the parent. e.g. If a plant variety was true breeding for a dominant train, all progengy would have dominant trait
What is the law of segregation?
Two alleles for a heritable character separate from each other during meiosis and end up in different gametes.
What is a test-cross?
A cross between a dominant phenotype (S?) and a homozygous recessive (ss).
What is the law of independent assortment?
Alleles for different traits assort independently of each other during Meiosis
Why did Mendel use pea plants?
- It’s easy to control mating in peas
- Peas have many easily-scored,
true-breeding, heritable traits
- Relatively short
generation times (one year), so
many experiments could be performed
- Peas make lots of offspring
Define qualitative variation
Either-or of alternative traits (red or pink)
Define quantitative variation
Many genes affect a trait and there are alleles at different loci.
Ex. Human height affect by alleles at 180 loci
Define evolution
Changes in allele frequencies in populations over time
Define population
A group of same species organism living in the same area at the same time. Interbreeding occurring
What process forms new alleles?
Mutation
What is a point mutation?
Substitutions of a single base in a gene. There can either be a protein change at higher levels or no protein change (silent point mutation).
What is an insertion/deletion mutation?
Addition/loss of one or more bases.
- Multiple of 3 bases results in loss of amino acid
- Non-multiple of 3 results in ALL amino acids changing (frame-shift)
What is a frame-shift mutation?
When a non-multiple of 3 amount of bases are inserted/deleted resulting in a change of ALL amino acids in that gene.
What is gene duplication?
What organisms are more susceptible to mutations?
Organisms with rapid generations times (divide frequently)
How does a mutation affect the phenotype of an organism?
Mostly negative
Sometimes neutral but RARELY positive
Are mutations goal directed?
No they arise randomly
How do mutation and sexual reproduction generate variation?
Mutation makes new alleles
Sexual reproduction shuffles alleles
A diploid organism can have at most how many different alleles at a particular locus?
2
Define gene pool
The sum of all copies of all alleles at all loci in a population.
What does it mean if a population is monomorphic or fixed at a particular loci?
There is only one allele at this locus
What are the 5 conditions for the Hardy-Weinberg Equilibrium?
- No mutation
- No gene flow
- Large population size
- No natural selection
- Mating is random
What are the 5 mechanisms of evolution?
- Mutation
- Gene flow
- Genetic drift
- Natural selection
- Nonrandom mating
Define gene flow
The movement of genes among populations which introduces new alleles. Tends to make populations more similar to one another
Define genetic drift
Random changes in allele frequencies due to random sampling errors. Small subset of population that do not reflect true allele frequencies reproduces.
*Strongest effect on small populations
What are the two special cases of genetic drift?
- Bottleneck - Population reduced dramatically (killed) resulting in reduced genetic variation
- Founder Effect - Immigrants break off and start new population
Define natural selection
Differential survival/reproduction of individuals in a population based on heritable variation in their phenotypes
What are two requirements of natural selection?
Heritable variation in phenotype and that variation affects survival/reproduction of individuals
Define relative fitness
The contribution an individual organism makes to the gene pool of the next generation relative to the contribution of others in that population
What are adaptations?
Heritable traits that increase survival/reproduction rates
What is Stabilizing Selection?
When the “Average” phenotype is most likely to survive
What is Directional Selection?
Phenotypes at one end of the distribution are most likely to survive (higher relative fitness)
What is Disruptive Selection?
Phenotypes at both ends of the distribution are most likely to survive (highest relative fitness).
*Mean phenotype has lowest relative fitness
Why doesn’t natural selection edit out alleles with least relative fitness?
- Hard to delete out recessive alleles
- Heterozygote advantage - Heterozygote RBC are better when malaria is present
- Frequency-dependent selection - allele frequency fluctuates back and forth. Ex: “left-mouthed” “right-mouthed” fishes
Why doesn’t natural selection create “perfect” organisms?
- It can only act on existing variation in a population
- Has to operate within universal physical/chemical properties
- Limited by historical constraints
- Adaptations usually require trade-offs among different traits
What is non-random mating?
When individuals choose mates with a particular genotype
- Prefferential mating with individuals of a different genotype - heterozygote frequency increase
- Prefferential mating with individuals of the same genotype - homozygote frequency increase
*DOES NOT affect allele frequencies*
What is sexual dimorphism?
Differences in appearance between male and females of the same species
What is sexual selection?
Reproductive success resulting from competition for fertilization
*DOES affect allele frequencies*
Compare intrasexual and intersexual selection
Intrasexual - competition between 2 males for the female (No female interaction)
Intersexual - Where female chooses the male based on a physical trait
What is the good genes hypothesis?
Females choose males since phenotype may be a reliable indicator of good traits so her offspring will be high quality
What is the sexy son hypothesis?
Female selects best phenotype becuase her offspring will be more likely to get a mate
What are the only evolutionary mechanisms that produce adaptation?
Selection (natural and sexual)
Does selection (natural and sexual) favor traits that are good for the population or the individual?
Individual
Define immutable
Not changing over time.
e.g. Early in science, biologists thought species were immutable
What is the morphological species concept and why do most biologists not use it?
States that organisms that look alike are of the same species.
This is problematic because some different species look very similar (cryptic species)
or
Some times males/females/juveniles of the same species look different
What is the biological species concept (BSC)?
Species are groups of actually/potentially interbreeding populations that are reproductively isolated from other such groups
Compare prezygotic and postzygotic reproductive barriers
Prezygotic - Before fertilization
Postzygotic - After fertilization
What are the 5 prezygotic reporductive barriers? Explain them.
- Habitat isolation - different habitat (land and water)
- Temporal isolation - different mating times during the year
- Behavioral isolation - individuals reject potential mates because of their behavior (breeding calls of frogs)
- Mechanical isolation - Genitalias don’t work together (shape, size, position)
- Gametic isolation - sperm and eggs don’t bind successfully
What are the 3 postzygotic reproductive barriers? Explain them.
- Reduced hybrid viability - hybrid offspring have developmental problems
- Reduced hybrid fertility - hybrid offspring have low fertility or are completely sterile
- Hybrid breakdown - F1 generation is fine but F2 generation has survival/reproducing problems
What was Lamarck’s hypothesis? Who disproved it?
Traits change by use or disuse and these changed traits are heritable (inheritance of aquired traits).
August Weisman disproved by cutting off the tails of mice and breeding them with one another and DISPROVED the inheritance of aquired traits hypothesis.
What 4 factors did Darwin base his hypothesis on?
- Voyage of The Beagle
- Knowlegde of “artificial selection”
- Knowledge of variation in nature
- Knowlege that all species have potential for rapid growth but rapid grown is rarely seen in nature - so some individuals die off
What is the Dobzhansky-Muller model?
When a single ancestral population dets divided into two separte populations and they evolve independetly
What is allopatric speciation?
“allo” = different; “patric” = fatherland
Population are initially separated geographically
What is a founder event?
When a group of individuals from a population cross a barrier to form a new isolated population.
Will probably lead to a founder effect - reduced genetic variablitly
What is sympatric speciation?
“sym” = together with; “patric” = fatherland
Reproductive isolation WITHOUT physical barrier
What are the 3 types of sympatric speciation? Explain them
- Disruptive selection on habitat preferenced - mating happens on preferred habitat only and speciation occurs over time ( flies on hawthorn fruit and flies on apples)
- Sexual selection - Females choice of males to mate with based on male triats like coloration
- Polyploidy - whole sets of chromosomes are duplicated
Compare autopolyploidy and allopolyploidy
Autopolyploidy - duplication within species
Allopolyploidy - combining chromosomes of two different species
*Happens via errors in mitosis or meiosis
What is autopolyploidy and in what organisms does it often happen?
Mitotic error leading to tetraploid cell which undergoes meiosis producing diploid gametes. If diploid sperm fertilized diploid egg - offspring is tetraploid
Often happens in organisms that can self-fertilize (plants)
Why does polyploidy lead to speciation?
When a tetraploid mates with a normal diploid, BAD things happen. Tetraploids become isolated from diploids
What is allopolyploidy?
Two different species mate forming a hybrid. (mule)
What is hybridization? Does hybridizaion occur in allopatric or sympatric speciation?
When populations that are becoming reproductively isolated begin to interbreed
Sympatric ONLY
What are the 3 outcomes for hybridization?
- Fusion - if substantial gene flow occurs, they fuse back into one
- Stability - Hybrid zone remains constant but hybrids are less-fit than pure-breds
- Reinforcement - natural selection strengthens prezygotic barriers. Mating is favored within species and hybridization is avoided
Reinforcement only occurs in ________
Zones of sympatry (where two species overlap)
Define evolutionary radiation
Rapid diversification of many species from a single ancestral species
What 4 factors determine the rate of speciation?
- Limited movement/dispersal
- Specialized diets; speciation in herbivore bugs higher than predatory bugs
- Speciation rate higher in animal-pollinated plants vs. wind pollinated
- Strong sexual selection
What are different alleles?
Different DNA sequences (version of the same gene) found at the same locus on homologous chromosomes
If each parent can produce 100 genetically distinct gametes, how many genetically distinct offspring can two parents produce?
100 X 100 = 10,000
What are two important observations Darwin made that helped shape his theory?
- Organisms within a populaiton vary
- Organisms produce more offspring that can be supported by the environment
What is artificial selection?
The breeding of plants and animals for particular traits by humans.
e.g. One example is the breeding of cows to produce offspring with higher milk yields
The smallest unit that can evolve is a __________
population
What is convergent evolution?
The independent evolution of similar traits in different lineages
If a new species of plant is to be produced by means of allopolyploidy from two parental species that are 2n = 4 and 2n = 8, how many chromosomes would you expect in the somatic cells of the new species?
12
The two gametes would be n = 2 and n = 4. They would combine for a total of 6, which after doubling would be 12.
A new species can arise in a single generation by __________.
Polyploidy - The diploid chromosome number changes
In a hybrid zone, what could lead to reinforcement?
- Reduced hybrid fertility/viability
- Sexual selection
- Hybrid breakdown
According to the punctuated equilibrium model of evolution, __________.
The tempo of evolution consists of abrupt episodes of speciation followed by long periods of equilibrium.
What is a polytomy?
Where a common ancestor has more than 2 sister taxa
*Node 5 below*
What is a clade?
A taxon that includes a common ancestor and ALL of its descendants
What is an ancestral trait?
A trait present in a common ancestor
What is a derived trait?
A trait that has changed from the ancestral version to something new
Define homologous trait
Similar traits shared between 2 or more taxa inherited from common ancestor
Define analogous trait
Similar traits shared by two or more taxa for reasons other than ancestry. Evolved via convergent evolution
Why are shared derived traits more useful than shared ancestral traits?
Because they are homologous traits that are found in two or more members of the ingroup, but not in the outgroup. These help us identify subgroups within the ingroup.
What are monophyletic groups?
Groups that consist of a common ancestor and all of its descendants – aka, a clade. This is good!
What are paraphyletic groups?
Groups that consist of a common ancestor and some (but not all) of its descendants. Bad!
*Group in Pink*
What are polyphyletic groups?
Groups that don’t include the most recent common ancestor of the group. Bad!
*Group in yellow*
