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Biology 2B lec 10
Mendelian Genetics
| Question | Answer |
|---|---|
| 1. Genes = ? 2. Gene Products ----> ? | 1. instructions for gene products 2. organism's phenotype |
| mitosis (begin with one diploid cell and end with 2 diploid cells) | - before prophase chromosome has duplicated forming 2 sister-chromatids. -metaphase, duplicated sister-chromatids line up in the middle & in the next stage they pull the pairs apart so one sister chromatid moves to the left & one to the right of the cell |
| what is the purpose of meiosis? | sexual reproduction and variation |
| what is the process of meiosis? | -chromosomes duplicate & instead has homologous pairs of chromosomes( 4 sisters) in the midline in meiosis. also can have crossing over occur in meiosis which doesn't occur in mitosis. |
| Mendel's 1st law of heredity: Law of segregation | -when any individual produces gametes, 2 copies of a gene separated/segregated so each gamete receives only 1 copy (a haploid 1N) -thus from every parent of the P generation, every individual of the F1 gen recieves one gene copy chosen randomly |
| why was Mendel so clever? | mendel knew that to study heredity, he had to study organisms that could interbreed (not usually possible w/ different species) -traits that varied w/i species -traits classified as 2 discrete classes -knew he needed to count frequencies. |
| how did Mendel extend Dalton's atomic theory of chemistry to inheritance? | dalton never saw an atom but reasoned that atoms must exist b/c of the fixed and simple proportions in which elements combine to form compounds |
| Mendel's inference from results of the monohybrid crosses | -each gamete(pollen/sperm/egg) contains only 1 facto, but the zygote contains 2-b/c it produces from the fusion of 2 gametes. -"factors" calles genes |
| Mendel's 2nd law of Heredity: Independent Assortment | cross peas differing in 2 characters, a dihybrid cross. 1. alleles of diff genes assort independently during gamete formation if they are on diff chromosomes 2. genes on the same chromosomes are physically linked & generally don't assort independently. |
| simple rules of probability theory | -multiplication rule: probability of 2 independent events happening together. -addition rule: probability of an event that can occur in 2 different ways. |
| moving on to greater genetic complexity phenotype not equal to genotype | 1. simple traits: dominance 2. co-dominance, incomplete, and partial 3. multiple traits @ single locus (pleiotropy) 4. Epistasis: interactions among loci in trait expression 5. multiple loci for a single trait (polygenic traits) 6. environmental eff |
| co-dominance | P: red x White F1: pink F2: .25(red), .50(pink), .25(white) |
| multiple alleles/traits | ex: ABO blood system |
| Epistasis | def: phenotypic expression of one gene is influenced by another gene -ex: 2-locus of coat color in labrador retrievers |
| did mendelian genetics solve the inheritance problem? | 1. biometricians vs. mendelians -bio. held darwin right & all evolution proceed by graduallly -thought mend. traits w/ large phenotypic effects, were special cases 2. mendelians thought NS ineffective & never produce new types. 3. quantitative genet |
| Nilsson-Ehle (1909) | effects of multiple loci on wheat chaff color polygenic traits |
| multiple loci lead to continuous/quantitative variation | -when a large enough number of genes influence a character, have a continuous, normal frequency distribution -mendel's characters discrete and qualitative -for most traits phenotypes vary cont. over a range (quantitative) |
| moving from individual genotypes to characteristics of pop | -NS acts on individual to create changes in the distribution of characters in the pop. |
| population genetics | p+q=1 |
| pop genetics: the hardy wienberg equilibrium | H-W eq: a fundamental theorem of pop genetics -makes set of null predictions about expected allelic & genotypic frequencies -H-W assumes a large pop, closed pop, random mating, = mating opp, & = survivorship if observed geno DNE expected at H-W->evoluti |
| things that follow from the H-W equilibrium | 1. @ H-W eq, genotypic frequencies will be determined exclusively by allele frequency 2. note that when 2 alleles & p=q=.5, expected ratio of homozygotes and heter is 1:2:1 as it was for mendelian genetics . |
| Hardy-Weinberg Theorem | in diploid organisms, allele frequencies & genotypic ratios in large biparental pop reach eq. in 1 gen and remain constant thereafter unless disturbed by: 1. mutations 2. genetic drift 3. genetic flow 4. non random mating 5. natural selection |
| causes of evolution: A.mutation | mutations occur randomly w/ respect to what might be adaptively beneficial in a particular selective regime. - must mutations are harmful or neutral, but if conditions change could become advantageous. |
| kinds of mutations | 1. point mutations - substituents ~silent (synonymous) ~missense (nonsynonymous) ~nonsense (nonsynonymous) - frameshift mutations ~basepair insertion/ deletion 2. chromosomal: duplications, deletions, inversions, translocations, transp |
| causes of evolution: A.mutation, 1. point mutations | alter a single point in base sequence a) substitution: replacement of single base nucleotide w/ another nucleotide ~silent: have no effect on sequence due to redundancy in DNA code ~missense:a change in DNA code causes change in sequence ~nonsense:ST |
| example of point mutation is sickle cell anemia: | a missense mutation a recessive character |
| point mutation ~frameshift mutation | occurs when basepair insertion or deletion causes sequence of codons to be read incorrectly |
| causes of evolution: A.mutation, 2. chromosomal mutations | large-scale mutations of whole genes or parts of chromosomes. ~gene duplication: happens during un= crossing over, maybe beneficial ~deletion: also un= crossing over, usually bad ~inversion: reduce recombination allowing genes to be transmitted as a un |
| causes of evolution: A.mutation, 3. mutation rates | -mutation can generate substantial variation across genome & in pop -however, b/c PER LOCUS mutation is low, mutations alone produce small deviations from H-W eq at locus. -if large deviations from H-W other evolution processes dominating. |
| spectacular exceptions | chromosomes form rings leading to high rates of reciprocal translocations & not independently assorting properly. major radiations of species w/ different ring forming attributes. ex: camissonia campestris |
| causes of evolution: B. Gene flow | -results from the migration of individuals & gametes( or other propagules like seeds/larvae) from 1 pop to another, & the incorporation (by successful interbreeding) of genes carrying into the novel gene pools |
| causes of evolution: B. Gene flow allele frequencies may be changed by: | -immigration (large effect if recipient pop is small) or -emigration (has a large effect if the source pop is small |
| gene flow has 2 important effects on evolutionary change at 2 levels: | 1. pops (microevolutionary consequences) -gene flow introduce new alleles to pop increasing genetic variation of pop and change allele frequencies. 2. among pops (macroevolutionary) -the less gene flow between 2 pop, more likely they will diverge & evo |
| causes of evolution C. genetic drift | -random change in allele frequencies & loss of alleles due to change -larger pops, LESS importance of drift -smaller pops, GREATER importance -2 demographic processes making drift strong & important: 1. founder effect 2. pop bottlenecks |
| founder's effect | if a new habitat is colonized w/ few individuals. allele frequencies will likely be changed simply by chance events that change rare alleles likely to be lost. ex: european starlings |
| pop bottlenecks | -similar to founder effects but occur when pop greatly reduced in size, happens through natural processes or humans -ex: fur seals -bottlenecks occur when species overharvested by humans, or when their habitat are reduced or fragmented extensively. |
| causes of evolution D. non-random mating | -occurs when individuals choose mates w/ particular genotypes/phenotypes, there are 2 types: 1. inbreeding 2. outbreeding 3. sexual selection 4. strong disparity |
| inbreeding | -called POSITIVE ASSORTATIVE MATING, occurs when individuals preferentially mate w/ same genotype as themselves -allele frequencies remain the same but HETEROZYGOSITY declines dramatically per generation |
| outbreeding | -called NEGATIVE ASSORTATIVE MATING, occurs when individuals avoid mating w/ similar genotypes (close relatives) -consequences: over-representation of heterozygosity ex: pin and thrum type flowers get pollinated between the species. |
| strong disparity | in mating opportunity. social dominance |
| genetic load | -the frequency of rare, deleterious alleles found in a pop that only express in a homozygous condition (recessive) -inbreeding depression -small pops b/x of increased relatedness & purge on deleterious alleles. |
| types of natural selection include: | 1. stabilizing 2. directional 3. disruptive 4. balancing 5. frequency-dependent 6. sexual 7. kin selection |
| the consequences of evolution | Natural selection increases, the frequency, across generations, of individuals w/ more advantageous alleles (or genotypes) relative to individuals w/ less advantageous alleles |
| causes of evolution E. Natural Selection | -if trait favored by selection is discrete & controlled by 1 or few alleles then examine evolution by studying change in allele frequencies over time. -many traits quantitative & controlled by many genes & environment -change in phenotypic distribution |
| causes of evolution E. Natural Selection heuristics graph | -human height a polygenic & quantitative trait |
| 3 common types of Natural Selection based on directionality w/ quantitative traits | - stabilizing selection: favors average phenotype -directional selection: favors individuals that are EITHER above or below average phenotype -disruptive/diversifying: favors individuals BOTH above AND below average. |
| stabilizing selection | 1. favors individuals w/ average phenotypes 2. reduces phenotypic variance for that trait -does not significantly change the mean ex: human birth weight |
| Directional selection | 1. shifts the mean value of trait 2. usually reduces phenotypic variance for that trait -directional selection favors more diverse individuals & leads to change in mean -ex: peppered moths |
| disruptive/diversifying selection | 1.has little effect on the mean of trait 2.INCREASES phenotypic variance for that trait 3.maintains genetic variation in a pop(form of balancing selection) ex:black-bellied seed crackers results in a bimodal phenotypic distribution & genetic variatio |
| character displacement in mustelids | mustellids appear to have communities structured by competition. diameter of upper canine predicts more regular distribution than expected by chance. |
| balancing selection | -heterozygote advantage/heterosis warfarin resistance in norway rats WsWs=susceptible WsWr=resistant (higher fitness) WrWr=resistant |
| frequency-dependent selection | ex: scale-eating cichlids -left/right mouthed fish increase in density when the the other has decreased b/c it has limited its resources and cycle cont. |
| positive frequency dependence | -more common a particular trait, more trait favored ex: snails & opp chirality could drive one or the other extinct by initial event of events |
| negative frequency dependence | -less common a particular trait, the more trait is favored. (gameotophytic self-incompatibility genes) ex: almonds |
| heritability | -proportion of phenotypic variability that is attributable to genetic variation |
| male zebra finches experiment | had colored feathers glued to their heads and selection for females choosing males acted swiftly on white feathers even though no heritability |
| density (frequency) independent selection | changes in allele frequencies driven by differential mortality set against a backdrop of non-selective mortality -ex: lethal recessive alleles |
| density (frequency) dependent selection | the density or frequencies of a character determines its relative success. includes differential reproductive contribution to next generation. allows alleles to spread in pop much faster than DIS |
| frequency dependent selection based on... | traits that confer mating advantages(disproportionate contribution to gene pool of next generation) can drive selection on quantitative characters over a brief period time |
| causes of evolution, N.S. sexual selection | differences in reproductive succes generated by differential success in competition for mates |
| unbalanced investment | -ANISOGAMY: un= gamete size between sexes difference in parental investment |
| beyond gamete production: more female investment bias | -differential gamete investment -differential cost of maturing fertilized eggs -differential investment in rearing young |
| sex roles | -bateman's curve -NS favors: ~low investors: seek many mates ~high investors: seek few, high quality mates ex: manakins w/ males making elaborate signals ex: female pipefish fight and ornamented for men |
| sex roles: males | males have LOWER parental investment in each offspring & have much to gain from multiple mating. hence males should mate as often as possible. if 1:1 sex ratio means competing for females by fighting or signaling |
| sex roles: females | have HIGH reproductive investment & low reproductive potential should mate more rarely & be selective, favoring males that have resources that benefit them or offspring |
| sexual selection 2 classic types | 1. intrasexual selection: direct competition among males for access to females. ex: elephant seal 2. intersexual selection: indirect competition among males to attract females; involves female choice |
| intrasexual selection | direct competition among males for access to females (weapons elephant seals & blue damselfly |
| intersexual selection | indirect competition among males to attract females, female choice |
| the 3 primary models of sexual selection by female choice: | 1. direct benefit 2. good genes 3) runaway sexual selection |
| 1. direct benefits | direct benefits: -access to male's territory -male parental investment -protection -help in raising offspring -avoidance of parasites ex: female willow warblers prefer males that sing @ high rate to obtain good territories |
| 2. good genes | females in many birds receive no direct benefits from males, so good genes or runaway sexual selection could each be benefits to mate choice |
| good genes vs runaway selection | 2 options: 1. genes for sexy males spread since the bearers preferred by choosy females-runaway selection 2. genes for quality spread b/c provide bearer a fitness advantage. -main evidence for runaway selection is extravagance of male traits |
| classic runaway selection argument | -costs: a) energy to build peacock mating display b) predator vulnerability -benefit: females choose on basis of signal reinforcing signal. -some evidence for female preference for arbitrary male traits that could allow runaway to get started |
| predicting behavior | -parental investment is a continuum -more similar the PI between sexes, more similar sex roles |
| phylogenetic tree | a schematic that portrays relatedness, divergence, and time |
| ancestral trait | trai common among the groups in a clade and found in the common ancestor |
| derived traits | traits that differ from ancestral group that help distinguish among different groups w/i clade |
| synapomorphy | shared derived trait among a group of organisms |
| homoplasies | convergent evolution to result in shared traits among groups that have independent histories. |
| use of half a wing? | 1. gliding down from trees 2. hopping up from ground 3. inclined running & climbing |
| phylogenic hypothesis | based on an assumption of parsimony ( simplest explanation is the one that is most likely true) |
| if interspecific interactions as agents of N.S. | then they favor traits that provide defense ex: peppered moths |
| parasites and disease can also function as "predators" to limit prey population | myxomatosis- disease caused by myxoma and introduced to australia to limit rabbit population b/c it give rabbits tumors through the virus |
| predator-prey interactions | victim: dV/Dt= rV-pVp predator/parasite= dP/dt= cpVP- d(p)P |
| when predator growth rate depends on prey pop and prey pop growth rate depends on predator pop | -an increase in prey pop followed by an increase in predator pop -increase in predator births causing an increase death rate in pry pop -w/ fewer prey available, predator pop decrease due to low birth rates. -cycle begins again |
| prey death due to predators density dependent | # of prey consumed per predator increases with prey density (functional response) |
| functional response | how # of prey consumed per predator changes with prey density -increase predator efficiency affect pop dynamics cycles b/c it would drive prey to extinction and predator's exponential growth to decrease. |
| prey has 2 kinds of density dependent mortality | 1. intraspecific competition for resources 2. predation |
| intraspecific competition | 1. slows rate of prey pop growth as it approaches K and stabilize 2. prevents predator explosions and resulting prey pop crashes. |
| lynx-hare pop cylces | 1. food limitations- prey overshoot K and periodically crash. 2. pure predator- predators increase in response to rising prey density and reduce prey density and cause predator starvation |
| evolution can play a big role in enemy-victim interactions b/c of strong selection | -rabbits evolved to resist virus (myxoma) - virus evolved in decreasing lethality b/c that way by not immediately killing the rabbit it can interact with other rabbits and pass on the virus before dying. |
| abiotic stresses | cold, drought, heat, wind, physical environment |
| biotic stresses | from organisms in environment much of selection comes biotic |
| strong selection can also drive predator-prey cycles | -chlorella, a tradeoff between predator resistance & competitive ability to reproduce. -predator @ high density when prey @ low density -prey @ high density when predator @ low density |
| competition (-,-) intraspecific | individuals sharing resources that is in short supply resulting in decreases rates of growth, survival/reproduction that alters growth rates. |
| competitive exclusion principle | 2 species that use the same resources in the same way cant coexist. one will drive the other to extinction (gause) -comp BETWEEN species works in the same way except that 2 species may have very different competitive abilities. |
| competition among barnacles on the scottish coast | B+r coexist with living in lower intertidal(B) and upper (r) -experiment where B placed in upper w/ r and they died out b/c couldn't tolerate being hot and dry. -r placed in lower w/ B in place where B moved & r happy and survived but when B regrew r di |
| mechanisms of competition 1. exploitative | resource depletion. ex: competition for food/nutrients |
| mechanisms of competition 2. interference | competitors confront each other to prohibit others from using resources ex: competition for space, territoriality |
| what we know about competition | 1. organisms compete for limiting resources 2. competitive exclusion principle if using same resources in same way at the same time & place 3. however species an coexist |
| resource partitioning | major way competitors coexist and a divergence of resource use. |
| eco-evolutionary processes -character displacement | process toward niche divergence as a result of interspecific competition -sympatry: comparing pop living in same location as another species -allopatry: living in an area w/o other species |
| species packing | adding new species shrinks the niche width of all species. to compensate species often become more specialized and efficient @ using narrower range of resources |
| species can also coexist a # of ways due to trade-offs | -strong competitors susceptible to predators -good colonizers often poor competitors |
| general features of competition | chipmunk species in SW U.S. live in mountain forests. Paterson found that when a chipmunks species lived alone on mountain range it occupied broader range of habitats & elevations than when competitor species lived with them |
| lotka-volterra equation what is a in the equation | measures the extent to which the use of resources by an individual of species 2 decreases the per capita growth rate of species 1 -when a=1, individuals of 2 species using identical in their effects. |
| 1. a12 2. a21 | 1. effect of species 2 on species 1 2. effect of species 1 on species 2 |
| what does it mean when 1. a=0 2. a=1 3. a close to one but less 4. a<<1 5. a>1 | 1. no niche overlap, in inter comp 2. complete niche overlap, strong inter comp 3. high niche overlap, strong inter comp 4. low niche overlap, weak inter comp 5. complete niche overlap and competition exclusion principle |
| coexistence occurs when | a12< (K1/K2) < a/a21 |
| altering outcome of competition | by environmental conditions, species interactions, disturbance, and evolution. -environmental conditions can result in competitive reversal (species that was the inferior competitor in one habitat becomes the superior competitor in another ex: beetles |
Created by:
dhgomez
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