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