New User Special Price Expires in

Let's log you in.

Sign in with Facebook


Don't have a StudySoup account? Create one here!


Create a StudySoup account

Be part of our community, it's free to join!

Sign up with Facebook


Create your account
By creating an account you agree to StudySoup's terms and conditions and privacy policy

Already have a StudySoup account? Login here

Biology 101 Week 1 Notes

Star Star Star Star Star
1 review
by: Denice Arnold

Biology 101 Week 1 Notes BIOL 102

Marketplace > University of Pennsylvania > Biology > BIOL 102 > Biology 101 Week 1 Notes
Denice Arnold
View Full Document for 0 Karma

View Full Document


Unlock These Notes for FREE

Enter your email below and we will instantly email you these Notes for Biological Principles II

(Limited time offer)

Unlock Notes

Already have a StudySoup account? Login here

Unlock FREE Class Notes

Enter your email below to receive Biological Principles II notes

Everyone needs better class notes. Enter your email and we will send you notes for this class for free.

Unlock FREE notes

About this Document

These are the notes for Life: The Science of Biology Chapter 21
Biological Principles II
Dr. Sniegowski
Class Notes
Biology, Bio, Bio102, Biol102




Star Star Star Star Star
1 review
Star Star Star Star Star
"Yes YES!! Thank you for these. I'm such a bad notetaker :/ will definitely be looking forward to these"
Kenneth Streich

Popular in Biological Principles II

Popular in Biology

This 6 page Class Notes was uploaded by Denice Arnold on Thursday January 21, 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 25 views. For similar materials see Biological Principles II in Biology at University of Pennsylvania.

Similar to BIOL 102 at Penn


Reviews for Biology 101 Week 1 Notes

Star Star Star Star Star

Yes YES!! Thank you for these. I'm such a bad notetaker :/ will definitely be looking forward to these

-Kenneth Streich


Report this Material


What is Karma?


Karma is the currency of StudySoup.

You can buy or earn more Karma at anytime and redeem it for class notes, study guides, flashcards, and more!

Date Created: 01/21/16
Bio Chapter 21 Thursday, January 14, 2016 8:22 PM Chapter 21 Mechanisms of Evolution (Life: The Science of Biology p. 427 - 446) RelationshipBetween Fact and Theory Evolution- the change in genetic composition of populations over time Drives the origin and extinction of species Gives rise to diversification Evolutionarytheory - understanding of the mechanisms of evolutionary change Darwin and Wallace introduced the idea of natural selection Darwin went on a five-year voyage around the world Took note of differences between species in South America and Europe Temperate regions in South America had similar species to temperate regions in Europe Galapagos islands housed animals found nowhere else Both Darwin and Wallace independently developed ideas of natural selection, Darwin developed his first, so he is more closely associated with the concept Three major propositions for evolution: 1. Species undergo mutations that allow change over time Offspring resemble parents, but are not identical to each other or to either parent 2. Divergent species share common ancestors Descentwith modification 3. Survival and reproduction of individualsbased on variation of traits Natural selection Mendel's work on genetic inheritance influenced ideas about the mechanisms of evolution Modern synthesis of genetics and evolution Genetic and phenotypic variation Phenotypes- physical expression of genes Observable characteristics (ie. eye color) An example of a trait of would be "brown eyes" Genotypes - genetic composition Alleles - different forms of a gene Locus - particular site on a chromosome (plural is loci) Gene pool - sum of all alleles at all loci in a population Genotypes do not alone determine phenotypes Dominant alleles may cause phenotypes to be produced by more than one genotype (ie. AA and Aa may be phenotypically identical) Mechanisms of EvolutionaryChange Evolution in biology refers to change in populations over time Individuals do not evolve, populations do Four important mechanisms of evolution in addition to natural selection (mutation, gene flow, genetic drift, and nonrandom mating) 1. Mutation Source of genetic variation is mutation - any change in the nucleotide sequence in an organism's DNA Mutations arise from imperfections in DNA replication - occur randomly Natural selection is the force that acts on this random variation, which results in adaptation Mutations can also restore genetic variation that other evolutionary mechanisms have removed Even low mutations rates cause considerable genetic variation Ex: If probability of a point mutation is 10^-9 per base pair, DNA would average 3 new point mutations (3 x 10^-9 x 10^-9) and each diploid zygote would have about six new mutations A population of 7 billion people would be expected to carry about 42 billion new mutations Allele frequency- proportion of each allele in the gene pool Genotype frequency- proportion of each genotype among individualsin the population Artificial selection - purposeful selection of phenotypes This force is controlled by humans (agriculturalists, plant breeders, dog breeders, etc.) Adaptation - process by which a favored trait evolves through natural selection Alsorefers to the trait itself Positive selection - selection for beneficial changes Purifyingselection - selection against deleterious changes 2. Gene flow 2. Gene flow Migration of individualsand movement of gametes between populations This phenomenon can change allele frequencies in populations If arriving individualscan survive and reproduce in new location, they may add new alleles to the population's gene pool Ex: migration of Neanderthals in modern non-African human populations Traits such as red hair entered new populations 3. Geneticdrift Random changes in allele frequencies from one generation to the next Occurs in small populations May produce large changes in allele frequency over time Particularly potent when a population is reduced dramatically in size due to environmental events Populationbottleneck- only a small number of individualssurvive an environmental condition Surviving population has a new allele frequency (different ratio of red to yellow beans) Populations are likely to lose much genetic variation Genetic drift alsooccurs when few pioneering individualscolonize a new region Foundereffect 4. Nonrandommating Preferential mating of individualswith either the same (homozygous)or different (heterozygous) genotype Nonrandom mating systems that do not affect the reproductive success of individuals in a population do not result in evolutionary change Only change genotype frequencies (not allele frequencies) Sexual selection - individualsof one sex mate preferentially with particular individuals of the opposite sex May favor traits that enhance chances of reproduction even if they reduce its chance of survival Ex: females more likely to reproduce with males with a conspicious trait even though it may increase the chance that the male would be seen or heard by the predator MeasuringEvolutionaryChange Evolutionary change can be measured by allele and genotype frequencies Calculating allele frequency: The sum of NAA, Naa, and Naa is equal to N, the total number of individualsin the population Total number of copies (found in the denominator of p and q) is represented as 2N because each individualis diploid (has two copies) Note that for a population with two alleles at a given locus: p + q = 1 q = 1 - p If there was only one allele at a given locus, the frequency would be 1 Monomorphic population - allele is said to be fixed Geneticstructure - frequencies of different alleles at each locus and frequencies of the different genotypes in a population Although two populations may have the same allele frequencies for A and a (thus the same gene pool), if they are distributed differently among individuals,the genotype frequencies of the two populations differ Hardy-Weinbergequilibrium Model in which allele frequencies do not change across generations Genotypic frequencies can be predicted from allele frequencies Applies only to sexually reproducing organisms Five principal mechanisms of Hardy-Weinberg equilibrium (exact inverse of the five mechanisms of evolution) 1. No mutation Alleles present in population do not change and no new alleles are added to the gene pool 2. No selection among genotypes Different genotypes have equal probabilities of survival and reproduction 3. No gene flow No movement of gametes (or individuals)in or out of population 4. Population sizeis infinite The larger a population, the smaller will be the effect of genetic drift 5. Mating is random These idealized conditions are never met, but hypothetically, if they were met… Frequencies of alleles at a locus will remain constant from generation to generation No evolutionary change After one generation of random mating, genotypes will occur as follows: Natural selection acts directly on phenotypes Therefore, natural selection acts indirectly on genotypes Fitness - reproductive contribution of a phenotype to subsequent generations relative to the contributions of other phenotypes Fitness is a function of the probability of those individuals surviving x the average number of offspring they produce over their lives Fitness is determined by relative rates of survival and reproduction Types of natural selection Stabilizingselection - favors average individuals Ex: human birth weight Babies who are lighter or heavier at birth than the population die at higher rates than babies whose weights are close to the mean Directionalselection - favors individuals that vary in one direction from the mean Over many generations, evolutionary trend is seen in the population When optimal phenotype is reached, stabilizing selection takes over When optimal phenotype is reached, stabilizing selection takes over Disruptiveselection - favors individualsthat vary in both directions from the mean Ex: two types of seeds most abundant (hard seeds and soft seeds) Birds with large bills that can crack hard seeds and birds with small bills that can crack soft seeds will be most likely to survive Gives rise to a bimodal bill-sizedistribution All three types of natural selection tend to reduce genetic variation within populations The Distributionand Maintenanceof GeneticVariation Neutral alleles - do not affect the fitness of an organism No better or worse than alternative alleles at the same locus Sexual recombination- crossing over and independent assortment of chromosomes during meiosis Short term disadvantages: Reduces the rate at which females pass genes onto their offspring Dividing offspring into separate sexes greatly reduces the overall reproductive rate Long term advantages: Generates endless variety of genotypic combinations Sexual recombination facilitates repair of damaged DNA Alsopermits the elimination of deleterious mutations Asexual organisms have no mechanism to eliminate deleterious mutations, which results in lower fitness Muller'sratchet - the accumulation of deleterious mutations Frequency-dependentselection - occurs when the fitness of a phenotype depends on its frequency in a population Clinal variation - pattern of gradual change in phenotype across a geographic gradient Constraintson Evolution Evolution can produce a wide variety of adaptive traits, but there are limitations If an allele does not exist in a given population, it cannot evolve, even if it would be highly favorable by natural selection All evolutionary innovations are modifications of previously existing structures Microevolutionarychanges - short-term changes in allele frequencies Macroevolutionarychanges - long-term changes in allele frequencies


Buy Material

Are you sure you want to buy this material for

0 Karma

Buy Material

BOOM! Enjoy Your Free Notes!

We've added these Notes to your profile, click here to view them now.


You're already Subscribed!

Looks like you've already subscribed to StudySoup, you won't need to purchase another subscription to get this material. To access this material simply click 'View Full Document'

Why people love StudySoup

Steve Martinelli UC Los Angeles

"There's no way I would have passed my Organic Chemistry class this semester without the notes and study guides I got from StudySoup."

Allison Fischer University of Alabama

"I signed up to be an Elite Notetaker with 2 of my sorority sisters this semester. We just posted our notes weekly and were each making over $600 per month. I LOVE StudySoup!"

Bentley McCaw University of Florida

"I was shooting for a perfect 4.0 GPA this semester. Having StudySoup as a study aid was critical to helping me achieve my goal...and I nailed it!"

Parker Thompson 500 Startups

"It's a great way for students to improve their educational experience and it seemed like a product that everybody wants, so all the people participating are winning."

Become an Elite Notetaker and start selling your notes online!

Refund Policy


All subscriptions to StudySoup are paid in full at the time of subscribing. To change your credit card information or to cancel your subscription, go to "Edit Settings". All credit card information will be available there. If you should decide to cancel your subscription, it will continue to be valid until the next payment period, as all payments for the current period were made in advance. For special circumstances, please email


StudySoup has more than 1 million course-specific study resources to help students study smarter. If you’re having trouble finding what you’re looking for, our customer support team can help you find what you need! Feel free to contact them here:

Recurring Subscriptions: If you have canceled your recurring subscription on the day of renewal and have not downloaded any documents, you may request a refund by submitting an email to

Satisfaction Guarantee: If you’re not satisfied with your subscription, you can contact us for further help. Contact must be made within 3 business days of your subscription purchase and your refund request will be subject for review.

Please Note: Refunds can never be provided more than 30 days after the initial purchase date regardless of your activity on the site.