BSCI 1511 Final Exam
mutations can be
beneficial, harmful (deleterious), or neutral
hierarchical classification
Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
extinction
cessation of existence of a species or group of taxa
postzygotic barriers
hybrid inviability hybrid sterility hybrid breakdown
inbreeding depression
reduces fitness by generating offspring homozygous for deleterious alleles
mutation as an evolutionary force
- mutation is common on a per gamete (or per genome) basis but is rare on a per gene basis - most mutations with phenotypic effects are deleterious and recessive - mutation alone has little effect on HW equilibrium, but provides the raw material for selection and evolution
artificial selection analogous to natural selection because
- of the artificial component of selecting for the desired traits - reduction of population size down to only individuals with those traits
positive assortative mating
(mating with LIKE genotypes) - decreases heterozygosity for the genes affecting the trait on average, heterozygotes decrease if similar genotypes are pairing, but only for the loci affecting the trait (decreased by half with each generation that adheres to complete positive assortative mating)
negative assortative mating
(mating with UNLIKE genotypes) - increases heterozygosity for the gene(s) affecting the trait On average, heterozygotes increase if dissimilar genotypes are pairing
sympatric speciation via autopolyploidy
- both chromosome sets are derived from the same species
limitations of the biological species concept
- cannot be applied to fossils - cannot be applied to asexual organisms - some organisms are morphologically and ecologically distinct, yet interbreed
possible outcomes of hybrid zones over time
- reinforcement: reproductive barriers where hybrids cease --> strengthened repro barriers - fusion: weakening of reproductive barriers and increase in hybrids - stability: continued production of hybrid individuals
natural selection does not imply perfection
1. can only act on existing variation 2. limited by historical constraints/aka raw materials 3. adaptations are often compromises 4. chance, natural selection, and the environment all interact
Darwin's postulates of natural selection
1. variation 2. inheritance 3. some leave more progeny than others 4. survival/reproduction are NOT random --> based on heritable trait variation
interval between speciation events can be
4,000 years to 40 million years, with an average of 6.5 million years - can require a change in few or many genes
bottleneck effect
A change in allele frequency following a dramatic reduction in the size of a population
genetic drift
A change in the allele frequency of a population as a result of chance events rather than natural selection.`
macroevolution
Evolutionary change above the species level. results from microevolution
coelacanths
Example of stasis "living fossils" - thought to have gone extinct 80 MYA, thus ~80 million years of stasis
hybrid sterility
F1 hybrid is viable, but has reduced fertility
effects of genetic drift (sampling error)
are stronger on smaller populations
variation in rates of mutation based on generation time, environment, and stress
GT: single-celled organisms and viruses have many more generations per unit of time than do larger ones ENV: many environmental conditions can directly increase the mutation rate Stress: under some conditions, increased mutation rates appear adaptive
two ways to not have random mating
assortative mating inbreeding
sympatric speciation
The formation of a new species as a result of a genetic change that produces a reproductive barrier between the changed population (mutants) and the parent population. No geographic barrier is present.
allopatric speciation
The formation of new species in populations that are geographically isolated from one another.
vicariance
The physical splitting of a population into smaller, isolated populations by the formation of a geographic barrier
Some populations evolve so slowly (for certain alleles) that
This slow evolution is indistinguishable from the non-evolving HW condition
members of a species are reproductively compatible
at least potentially. they cannot interbreed with other populations
in rare cases, mutations may be
beneficial
over time, directional selection causes
a change in the mean value of a character in a population that is either higher or lower than its current mean value, resulting in a shift in the plot of trait frequency
speciation
a lineage-splitting event that produces two or more separate species
Selection coefficient (s)
a measure of the relative intensity of selection against a given genotype (S = 1 - W)
cladistics
a way of organizing information according to similarities, in biology it is used to assess what organisms are more similar to each other (we then assume this correlates with ancestry)
stasis
absence of evolutionary change in one or more characters for some period of evolutionary time
selection is a blend of chance and sorting
chance: new genetic variations arise by chance through mutation and recombination sorting: beneficial alleles are favored by natural selection, whereas deleterious ones are removed
Founder effect
change in allele frequencies as a result of the migration of a small subgroup of a population - newly founded populations don't always represent the genetic diversity in their sources
nonsynonymous mutation
changes in nucleotides that change amino acids
Character change
changes in the characteristics of organisms over time can occur quickly or slowly, in a single direction (such as evolving additional segments) or in reverse (gaining segments then losing them), and can occur within a single lineage or across several lineages
mutations
changes in the nucleotide sequence of DNA and can involve changes of one or many nucleotides cause new genes and alleles to arise
the morphological species concept
characterizes a species by body shape and other structural features
the ecological species concept
characterizes species in terms of their ecological niches
natural selection drives adaptive evolution by
consistently increasing the frequency of alleles that provide reproductive advantage
mechanical isolation
copulation occurs but no gametes transfer ex. mismatched snails
industrial melanism
darkening of populations of organisms over time in response to industrial pollution in the peppered moth
over time, stabilizing selection
decreases variation and stabilizes the mean of a trait in population around a particular, usually optimal value
the phylogenetic species concept
defines a species as the smallest group of individuals that share a common ancestor, forming one branch of the tree of life
chromosomal mutations that delete, disrupt or rearrange many loci are typically
deleterious
intrasexual selection
direct competition among individuals of one sex (often males) for mates of the opposite sex
synonymous mutation
do not change the encoded amino acid
male showiness
due to mate choice can increase chances of attracting a female while also decreasing his chances of survival ex. tail length negative survival value but positive attractiveness to females
natural selection increases the frequency of the alleles that
enhance survival and reproduction
cladistics allow us to identify cases of convergent evolution
ex. snakes and glass lizards
HW as a functional null
example of PKU alleles
directional selection
favors individual at one end of the phenotypic range (Ex. tusklessness) homozygote advantage
disruptive selection
favors individuals at both extremes of the phenotypic range heterozygote disadvantage
stabilizing selection
favors intermediate variants and acts against extreme phenotypes heterozygote advantage
hybrid inviability
fertilization occurs, but F1 hybrid has reduced viability
incompatibility
gametes are transferred, no fertilization
inbreeding and assortative mating can only affect
genotype frequencies, not allele frequencies so their effects may be quite ephemeral and may be reversed within one generation of random mating
sympatric speciation can occur via
habitat differentiation, polyploidy, sexual selection
heterozygote advantage (overdominance)
heterozygote has greater fitness than either homozygote; results in balanced polymorphism
heterozygote disadvantage (underdominance)
heterozygote has lower fitness than either homozygote
sex-based variability in rates of mutations
in humans, the rate of point mutations is 5X higher in sperm than in eggs, so fathers contribute most harmful mutations
disruptive selection over time
increases variation by favoring extreme phenotypic values, even if the mean of the distribution does not change
2 types of sexual selection
intrasexual and intersexual
speciation, the origin of new species,
is the key point where microevolution and macroevolution intersect
assortative mating
like genotypes either mate with each other or avoid each other
macroevolution is the cumulative effect of
many speciation and extinction events
inbreeding
mating among individuals that are more closely related than those drawn by chance from the population changes genotype frequencies by increasing the proportion of homozygotes and reducing heterozygotes across the entire genome (loss of heterozygosity across genome = loss of diversity)
postmating barriers
mechanical isolation incompatibility hybrid inviability hybrid sterility hybrid breakdown
much of the variation in natural populations is maintained by
mutation and genetic drift, as well as diploidy (in the form of recessive alleles hidden from selection in heterozygotes) some variation is maintained due to the action of selection
two processes produce the variation in gene pools that contributes to differences among individuals
mutation and sexual recombination natural selection then acts upon this variability
Max delbruck
mutation is a random process with no foresight
sexual selection
natural selection for mating success can result in sexual dimorphism, marked differences between the sexes in secondary sexual characteristics
when genes are left intact my a mutation that mutations is typically
neutral
balancing selection
occurs when natural selection maintains stable frequencies of two or more phenotypic forms in a population (balanced polymorphism) includes: heterozygote advantage, and frequency-dependent selection
The relative fitness W
of the most fit genotype in a population is, by definition, W=1 all other genotypes are scaled as a fraction of the most fit genotype
intersexual selection
often called mate choice; occurs when an individual of one sex is choosy in selecting their mate
selection has a very hard time acting on
people who are carriers of recessive diseases
temporal or habitat isolation
potential mates do not meet
ethological, behavioral, or sexual isolation
potential mates meet but do not mate - Ex. mate at diff times of year
hybrid breakdown
reduced viability/fertility in F2 or backcross hybrids
hybrid zones
regions in which members of different species with incomplete reproductive barriers meet and mate, producing at least some hybrid offspring
a classic example of heterozygote advantage
sickle cell allele maintenance in areas where malaria is endemic
the biological species model
species are groups of actually or potentially interbreeding populations, which are reproductively isolated from other such groups
premating barriers
temporal or habitat isolation ethological, behavioral, or sexual isolation
prezygotic barriers
temporal or habitat isolation ethological, behavioral, or sexual isolation mechanical isolation incompatibility
sympatric speciation via allopolyploidy
the chromosome sets are derived from different species
fitness
the contribution an individual makes to the gene pool of the next generation
relative fitness
the contribution of a genotype to the next generation, compared with the contributions of alternative genotypes for the same locus
reproductive isolation
the existence of biological factors (barriers) that impede two species from producing viable, fertile hybrids the reduction of gene flow between populations, so that populations diverge in allele frequencies (by genetic drift or by natural selection) and become reproductively isolated
frequency-dependent selection
the fitness of any morph declines if it becomes too common in the population ex. left-mouthed vs right-mouthed fish
selfing
the most extreme form of inbreeding - has effects just like positive assortative mating, but across the whole genome
dispersal
the movement of organisms from one place to another place that is not yet inhabited
gene flow
the transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes (can also change allele frequencies) tends to reduce variation among populations over time
good genes hypothesis
theory of sexual selection that argues individuals develop impressive ornaments to show off their efficient metabolism or ability to fight disease - if a trait is related to male genetic quality or health, both the male trait and the female preference for that trait should increase in frequency
adaptations
traits that have evolved through the mechanism of natural selection
point mutation rates are generally
very low about one mutation in every 10,000 genes per generation MUTATION ALONE IS A WEAK EVOLUTIONARY FORCE
If you have a dominant phenotype/genotype, then
you would assume that the W of the homozygous dom = heterozygous > W of the homozygous rec fitness of first two is equal since they are the same phenotype
If you have an incomplete dominant phenotype/genotype, then
you would assume that the W of the homozygous dom > heterozygous > homozygous rec