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Biology 102, Week 1 Notes

by: Cambria Revsine

Biology 102, Week 1 Notes BIOL 102,

Marketplace > University of Pennsylvania > Biology > BIOL 102, > Biology 102 Week 1 Notes
Cambria Revsine
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These notes cover material from our first full week of class, chapter 21, Life: The Science of Biology
Biological Principles II
Dr. Sniegowski
Class Notes
Science, Biology




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This 6 page Class Notes was uploaded by Cambria Revsine on Sunday February 7, 2016. The Class Notes belongs to BIOL 102, at University of Pennsylvania taught by Dr. Sniegowski in Spring 2016. Since its upload, it has received 17 views. For similar materials see Biological Principles II in Biology at University of Pennsylvania.

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Date Created: 02/07/16
Biology 102—Week 1—Chapter 21 Lecture 1:   All species lines have evolved to this point because of adaptations that make organisms  more fit for survival:  Adaptation: changes to more successful traits in a population over time o Camouflage, mimicry, makeup of cells etc.  Diversity and unity: balance between differences that set species apart, and the concept  that all species, and smaller subgroups of species, share certain similarities  o Why similar organisms tend to live closer than non­similar organisms  Natural Selection discovered by Charles Darwin during his Beagle voyage from Britain  to Galapagos Islands and around the world (1831­1836) o Same ideas were discovered by Alfred Russel Wallace, Wallace wanted to publish his ideas which persuaded Darwin to finally publish On the Origin of Species  (1859)  Species evolve over time  Species share common ancestors and branched off gradually (Darwin  developed early phylogenetic tree concept)  Species change because of natural selection  *Theory of Evolution* Evolution explains reasoning for adaptation and diversity, and natural  selection is the primary cause of evolution  Lecture 2:  Evolution: change in allele frequency of a population over generations o Individuals develop, populations evolve  Alleles: different forms of a gene o At each genetic locus of an individual, there are two alleles, one from the mother  and one from the father o In a population, there can be many alleles for a given gene, but allele frequency  always sums to 1.0 Evolutionary Biology:  Darwin­Wallace (1858)  Gregor Mendel: Mendelian inheritance (early 1900s) o Darwin and Mendel did not know about genes Four Evolutionary Forces­ Forces that alter allele frequency:   Selection: fitness differences among individuals in a population mean those that are good at survival and/or reproduction are selected for, causes the evolution of adaptive features  Genetic Drift: random change in allele frequencies by chance in a population because  populations are finite, most prominent in small populations  Migration (gene flow): change in allele frequency from individuals joining or leaving a  population  Mutation: Spontaneous change of the base pairs of an individual’s DNA, it can change  the overall allele frequency of a population but often very slowly o the ultimate source of allele variation that is acted on by the other three sources Calculating Allele and Genotype Frequencies: 1. Begin with number of individuals in a population with AA (homozygous dominant), Aa  (heterozygous), and aa (homozygous recessive) genotype  2. Find frequencies of both alleles: 2N +AA Aa Frequency of allele A:  p=   2N 2N aa Aa Frequency of allele a:  q= 2N *N= number of individuals, Nxx number of individuals with specific genotype *2N= number of individuals x2, aka number of alleles in the population *p + q = 1 3. Find frequencies of the three genotypes: N AA Frequency of genotype AA:  N N Frequency of genotype Aa:  Aa N N aa Frequency of genotype aa:  N 4. If you are given the genotype frequencies, to find allele frequencies: Frequency of p: Frequency of AA + ½ frequency of Aa Frequency of q: Frequency of aa + ½ frequency of aa 5. If you are given the allele frequencies, to find the genotype frequencies: 2 Frequency of AA: p Frequency of Aa: 2pq Frequency of aa: q2 Hardy Weinberg equilibrium: hypothetical situation where no evolutionary forces are acting  on a population and mating is random  “no evolution”; genotypic and allelic frequencies stay the same  1.) Selection Produces Adaptations: 1. Variation for a trait (from mutation/ allele differences) 2. Different fitness rates (survival and/or reproduction) depending on trait value 3. Transmission of trait value to next generation (must be heritable) 4. Change in allele frequency, higher proportion of the population now has the  advantageous trait Natural Selection Example: The peppered moth, Biston betularia, in 19  and 20  century Britain  Two forms were studied o typical form (typica), light­colored  o melanic variant (carbonaria), dark­colored, first noticed at 1% in 1848  Manchester (highly polluted area), rose to 98% of population in 1895    Carbonaria were found to be located in correlation with polluted areas acroth the  country, which declined after the induction of anti­pollution laws in mid­20  c.  Scientists tested the hypothesis that Carbonaria’s dark color gave them a selective  advantage in highly polluted areas and vice­versa with typica by tracking rates of bird  predation both in a controlled experiment and using mark­release­recapture methods in  nature; this hypothesis was proven true  Proved that bird predation was the natural selective cause of the increase of Carbonaria Lecture 3: Genotype + Environment = Phenotype (Both nature and nurture) *Selection acts based on phenotype (differences in how traits are expressed in real life), not  genotype *However, evolution only occurs due to genetic variation, not affected by environmental  variation   Patterns of Selection:  Most traits are not simple one­locus genes, but are affected by environment and many  different gene loci  quantitative traits   Exhibit a bell­shaped curve  In quantitative traits, changes in allele frequency of multiple genes is the basis of their  evolution   Three main patterns of selection (trait value along the x­axis, fitness of trait y­axis): If the trait value is most fit at intermediate value (i.e. medium height), average trait value of  population will condense to the middle, away from outliers  If the trait value is most fit at one extreme (i.e. slim beaks), average trait value will shift to one  end, away from the end that isn’t as fit anymore  If the trait value is most fit at either end of value scale (i.e. light or dark coloring), average trait  value will split to both extremes, in some cases can divide a population/ species into two variants Sexual selection: access to mating depends on traits  Intra­sexual selection: traits that make individuals better at competing with others of the  same sex for mates   Inter­sexual selection: traits that make individuals more attractive to members of the  opposite sex *Usually in a situation of sexual reproduction where one sex (usually females) expends more  energy than the other on gametes (eggs and sperm), so the males usually compete for females * Often a trade­off for males between survival and mating (showiness can be disadvantageous in  survival)   Artificial Selection: controlled selection over breeding by humans on plants and animals  i.e. dog domestication from wolves; chickens selected for size, meatiness 2.) Genetic Drift:   Chance events outside of phenotype/genotype can affect survival and reproduction o random injuries, weather  So, allele frequency changes randomly in each generation in all finite populations  The smaller the population, the greater the effect of randomness –genetic drift  The probability an allele will go to fixation (frequency = 1) equals its starting frequency Bottleneck Effect:  A population might start out with near equal allele frequencies, but due to a chance disaster, only a small percentage of the population survives that has much different allele frequencies for traits  from the original ones  Cheetahs have gone through bottleneck effect; their population has greatly reduced in the  last decade resulting in 0% heterogeneous gene loci for the 52 surveyed More consequences of genetic drift:  Harmful alleles might increase in frequency, and rare advantageous alleles might be lost  Bottleneck effect might increase prevalence of rare genetic diseases o Ellis­van Creveld (EVC) syndrome in Amish due to founder effect (like  bottleneck effect, when a small subset of a population leaves the pop.) 3.) Migration (gene flow):  From individuals and gametes moving between populations  Can add new alleles a population/ change existing frequencies 


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