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 Lecture 3 - Exam 1

by: Devin Mart

Biology Lecture 3 - Exam 1 BIO 121 A

Marketplace > Missouri State University > Biology > BIO 121 A > Biology Lecture 3 Exam 1
Devin Mart
GPA 3.82

Preview These Notes for FREE

Get a free preview of these Notes, just enter your email below.

Unlock Preview
Unlock Preview

Preview these materials now for free

Why put in your email? Get access to more of this material and other relevant free materials for your school

View Preview

About this Document

The Evolution of Populations
General Biology
Dr. Durham
Class Notes
Biology 120 - General Biology
25 ?




Popular in General Biology

Popular in Biology

This 5 page Class Notes was uploaded by Devin Mart on Tuesday March 29, 2016. The Class Notes belongs to BIO 121 A at Missouri State University taught by Dr. Durham in Spring 2016. Since its upload, it has received 10 views. For similar materials see General Biology in Biology at Missouri State University.


Reviews for Biology Lecture 3 - Exam 1


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: 03/29/16
   Mart 1  Lecture 3: The Evolution of Populations    ● A population, not its’ individuals, evolve (it evolves as a whole).  ○ Evolution on scale of populations is due to microevolution​ ­evolutionary change  within a species or small group of organisms, especially over a short period.  ○ Population genetics ​ is the study of the distribution and change in frequency of  alleles within populations.  ■ This emphasizes extensive genetic variation within populations and  recognizes importance of quantitative characters.  ○ Modern synthesis​  emphasizes:  1. The importance of populations as the units of evolution.  2. The central role of natural selection as most important mechanism of evolution.  3. The idea of gradualism to explain how large changes can evolve as an  accumulation of small changes over long periods of time.  ● A ​ population​ is a localized group of individuals that belong to the same species.  ○ A ​ species is a group of populations whose individuals have the potential to  interbreed and produce fertile offspring in nature.  ○ Members of a population are more likely to breed with members of same  population than with members of other populations  ● A ​ gene pool is the stock of different genes in an interbreeding population.  ○ All ​allelesat the gene loci in all individuals of a population.  ○ Each locus is represented twice in a genome of a diploid ­ (of a cell or nucleus)  containing two complete sets of chromosomes, one from each parent.  ■ Individuals can be homozygous or heterozygous for these homologous  loci.  ● The Hardy­Weinberg Theorem​  ­ states that allele and genotype frequencies in a  population will remain constant from generation to generation in the absence of other  evolutionary influences.  ○ Populations at Hardy­Weinberg equilibrium must satisfy 5 conditions:  1. Very large population size ­ in small populations, chance fluctuations in a gene  pool can cause genotype frequencies to change over time.  2. No migrations​  ­ gene flow, transfer of all alleles due to the movement of  individuals or gametes into or out of our target population can change the  proportions of alleles.  3. No net mutations ​­ if one allele can mutate into another, the gene pool with be  altered.  4. Random mating​  ­ if individuals pick mates with certain genotypes, then the  mixing of gametes will not be random and the Hardy­Weinberg equilibrium does  not occur.     Mart 2  5. No natural selection​ ­ if there is differential survival or mating success among  genotypes, the frequencies of alleles in next variation will deviate from  frequencies predicted by Hardy­Weinberg equation.  ○ Evolution usually results when any of these five conditions are not met, when a  population experiences deviations from the stability predicted by the  Hardy­Weinberg theory.  ● Microevolution​  is the generation to generation change in a population’s frequencies of  alleles.  ○ Four factors can alter allele frequencies in a population:  1. Genetic drift  2.Natural selection​  3.Gene flow​  4. Mutation  ● Genetic drift ​ occurs when changes in gene frequencies from one generation to another  occur because of chance events (sampling errors) that occur when populations are finite  in size.  ● Bottleneck effect ​ occurs when number of individuals in a larger population are  drastically reduced by a disaster.  ○ Some alleles are overrepresented, other underrepresented, some entirely  eliminated.  ○ This is an important concept in conservation biology of endangered species.  ● Founder effect ​ is when a new population is started by only a few individuals and a gene  pool of a larger source population is not represented.  ○ Demonstrated in human populations that started from a small group of colonists.  ● Gene flow​  is a genetic exchange due to migration of fertile individuals or gametes  between populations.  ○ Migration of people throughout the world is transferring alleles between  populations that were once isolated, increasing the gene flow.  ● A m ​utation ​is a change in an organism’s DNA.  ○ Generally there is not much quantitative effect on large population in a single  generation.  ○ A long term mutation is important to evolution, the original source of genetic  variation that serves as raw material for natural selection.  ● Genetic variation occurs within and between population.  ○ Variation in a population is because of a  combination of inheritable and  non­inheritable traits.  ○ Phenotype​  are observable characteristic of an organism, a product of inherited  genotype and environment influences.  ■ Example: Genetically identical at coloration loci emerge at different  seasons.  ○ Only genetic component of variation is evolutionary consequences is a result of  natural selection.     Mart 3  ■ Only inheritable traits pass from generation to generation.  ○ Variation within a population can be both quantitative and discrete characters.  ■ Quantitative characters​  vary along a continuum within a population.  ● Example: plant height in wildflower population.  ● This is usually due to polygenic inheritance ­ the additive effects of  two or more genes influence a single phenotypic character.  ■ Discrete characters ​ are usually determined by a single locus with different  alleles, this has a distinct impact on phenotypes.  ● Polymorphism​  occurs when two or more discrete characters are present and noticeable  in a population.  ○ Population geneticists measure genetic variation ­ the level of whole genes and  the molecular level of DNA.  ● Gene diversity​  is the average percent of gene loci that are heterozygous.  ● Nucleotide diversity ​ is the level of difference in nucleotide sequences among individuals  in a population.  ● Geographic variation ​ results from differences in genetic structure between populations  or between subgroups of a single population ­ inhabitants of different areas.  ○ This results from natural selection or genetic drift.  ○ Geographic variation in form of graded change in a trait along a geographic axis  is a cline ​ ■ Example: the average body size of many North American species of birds  and mammals increases with higher latitudes.  ○ In contrast to clines, isolated populations typically demonstrate discrete  differences..  ■ Example: house mice ­ isolate populations developed, some evolved  differences in karyotypes probably through genetic drift.  ● Mutation and sexual recombination generate genetic variation​ .  ○ New alleles originate only by mutation.  ■ Most point mutations only affect a single bases, usually harmless.  ■ Mutations alter protein structure/function and are more likely to be  harmful than beneficial.  ■ Chromosomal mutations affect many genes, likely to disrupt proper  development of an organism. ­   ■ Duplications of chromosome segments, whole chromosomes, or sets of  chromosomes are nearly always harmful.  ○ Because microorganisms have very short generation times, mutation generates  genetic variation rapidly.     Mart 4  ○ Organisms ­ sexual reproduction, most of the genetic differences are due to  unique recombinations of existing alleles from the population gene pool, ultimate  origin of allelic variation is past mutations.  ● Diploidy and balanced polymorphism preserve variation.​   ○ Tendency for natural selection to reduce variation is countered by mechanisms  that preserve or restore variation ­ diploidy and balanced polymorphisms.  ■ Diploidy is eukaryotes prevents elimination of recessive alleles by  selection because they do not impact the phenotype in heterozygotes.  ○ Balanced polymorphism​  maintains genetic diversity in a population via natural  selection.  ■ 1st mechanism ​ ­heterozygote advantage​  ­ heterozygous at particular locus  have greater survivorship and reproductive success than homozygotes.  ■ 2nd mechanism​  ­frequency dependent selection​  occurs when reproductive  success of any one morph declines if phenotype becomes too common in  population.  ● Natural selection as the mechanism of adaptive evolution.​   ○ Adaptive evolution is a trait with a current functional role in the life of an  organism that is maintained and evolved by means of natural selection.  ■ Chace creates new genetic variations by mutation and sexual  recombination.  ■ Sorting by natural selection favors propagation of some variations over  others, this produces organisms that are a better fit to their environments.  ○ Evolutionary fitness is the relative contribution that an individual makes to the  gene pool of the next generation.  ■ Reproduction success depends on a variety of factors.  ■ Example: slight differences in flower shape, color, or fragrance may lead  to differences in reproductive success.  ○ Darwinian fitness​  ­ a contribution an individual makes to the gene pool of the  next generation relative to contributions of other individuals.  ○ Relative fitness​  ­ contribution of one genotype to the next generation compared  to contributions of alternative genotypes for the same locus.  ■ Survival alone does not guarantee reproductive success ­ many factors  affect both survival and the determination of evolutionary fitness.  ■ Through differential survival and reproductive success of phenotypes,  natural selection adapts a population to its environment by increase or by  maintaining favorable genotypes that produce better phenotypes in the  gene pool.  ● Natural selection affects frequency of a heritable trait in a population leading to:     Mart 5  ○ Directional selection​  ­ most common during periods of environmental change or  when members of a population migrate to a new habitat with different  environmental conditions.  ○ Diversifying selection​  ­ occurs when environmental conditions favor individuals  at both extremes of the phenotypic range over intermediate phenotypes.  ○ Stabilizing selection​  ­ favors intermediate variants and acts against extreme  phenotypes, this reduces variation and maintains predominant phenotypes.  ● Natural selection maintains sexual reproduction.​   ○ Sex is an evolutionary enigma, inferior to asexual reproduction as measured by  reproductive output (number of individuals that can reproduce).  ○ Sex must confer some selective advantage to compensate for costs of diminished  reproductive output.  ■ Most eukaryotes maintain sex, even in species that can reproduce  asexually.  ■ Sex provides a mechanism for changing the distribution of alleles and  varying them among offspring.  ○ Reasons why natural selection cannot produce perfection:  1. Evolution is limited by historical constraints.  2. Adaptations are often compromises.  3. Not all evolution is adaptive.  4. Selection can only edit existing variations. 


Buy Material

Are you sure you want to buy this material for

25 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

Jim McGreen Ohio University

"Knowing I can count on the Elite Notetaker in my class allows me to focus on what the professor is saying instead of just scribbling notes the whole time and falling behind."

Kyle Maynard Purdue

"When you're taking detailed notes and trying to help everyone else out in the class, it really helps you learn and understand the I made $280 on my first study guide!"

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."


"Their 'Elite Notetakers' are making over $1,200/month in sales by creating high quality content that helps their classmates in a time of need."

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.