Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Chapter 12 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display *Populations vs. Species A species is all the organisms potentially capable of naturally breeding among themselves and having offspring that could successfully interbreed. A population is a group of organisms in the same species in the same geographical area.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display *Population Genetics and Gene Pools Population genetics is the study of the kinds of genes (alleles) within a population. – Also accounts for the numbers of alleles in a population – Predicts and observes how those numbers will change over time – This data is used to classify organisms and study evolutionary change.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Population Genetics and Gene Pools In a population – Each individual has a set of alleles. Diploid organisms have 2 alleles at most. – The population may contain more different alleles than any one individual. The human population has 3 alleles for blood type. All of the alleles in a population make up the gene pool.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Genes, Populations, and Gene Pools

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Biological Species Concept According to the biological species concept, species is a group of organisms – That share a common gene pool – That are reproductively isolated from other populations They do not exchange genetic information. Local populations of a single species may have slightly different allele combinations.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Gene and Allele Frequencies Differences in gene frequencies reflect genetic differences between populations. Allele frequency is a measure of how often an allele is found in a population. – Expressed as a decimal or percentage – # of times an allele appears in a population/the total number of alleles in the population

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Allele Frequencies Differ in the Human Population

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Allele Frequencies, Dominance and Recessiveness Allele frequencies are unrelated to whether the allele is dominant or recessive. There are many instances where a recessive allele is more frequent in a population. Blue eyes & light hair are recessive traits that are more frequent in European regions.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Monday 12-10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Homework Ch 12 Concept Review #10 Ch 13 Concept Review 2, 4, 5, 6, 7, 8, 14, 15, 16, 17, 18, 19,

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Review from Ch 10 Do these on paper; try to do without notes If a pink snapdragon is crossed with a white snapdragon, what phenotypes can result, and what is the probability of each phenotype? In certain pea plants, the allele for tallness is dominant over the gene for shortness. – If a homozygous tall and a homozygous short are crossed, what will be the phenotype and genotype of the offspring? 12-12

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. How Genetic Diversity Comes About Genetic Diversity: term used to describe genetic differences among members of a population High genetic diversity Low genetic diversity How is genetic diversity related to population size? Why is low genetic diversity a serious disadvantage for a population? 12-13

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mechanisms introducing genetic diversity Mutations Sexual reproduction Migration 12-14

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Mutations Mutations are changes in the base sequence of DNA. Mutations are the source of new alleles. – All alleles originated with mutations. – Most mutations are harmful. – Occasionally a mutation will change a gene so that the protein works differently or better. Example: Insecticide resistance in mosquitoes

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Sexual Reproduction Sexual reproduction generates new genetic combinations. – New combinations of alleles in individuals May not necessarily change the frequency of alleles in a population – However, the new combination of alleles in an individual may create a combination of traits that allows the individual to survive and reproduce more successfully than other individuals. Example: Corn plants that inherit resistance to corn blight and resistance to insects

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Migration Migration is the movement of individuals into and out of populations. – Results in alleles being added or subtracted from a population Artificial migration is used in zoos to generate genetic diversity. – Inbreeding has reduced genetic diversity in small zoo populations. – Zoos are exchanging animals for breeding to introduce new alleles into their populations.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Importance of Population Size Will migration, mutation, or accidental death have a bigger effect in a large population or a small population? 12-19

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display The Importance of Population Size Population size is directly related to genetic diversity. – The smaller the population, the less genetic diversity a population can contain. Mutations, migrations and death can have dramatic effects on the genetic make-up of a population. Frequently, random events will significantly change the gene pool. – This is called genetic drift

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Drift The gene pool of a small population may not have the same proportion of alleles as the previous generation. Red frogs were eliminated and failed to breed. Their genes were not passed on to the next generation. As a result, frequencies of genes change in the gene pool. (Drawing) 12-21

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Drift 12-22

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Why Genetically Distinct Populations Exist Many species have wide geographic distribution with reasonable distinct subspecies. (What’s a subspecies?) This occurs for several reasons. Why do you think distinct subspecies exist?

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Adaptation to Local Environmental Conditions Genetic diversity allows populations to adapt to their specific environments. – Some individuals will have combinations of alleles that allow them to survive and successfully reproduce in hostile conditions. Death and migration remove or reduce the alleles that do not contribute to survival. – Example: Lizards in the desert have lighter coloration than those that live in other environments.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Which lizard is more likely to survive to pass on its genes in this environment? Why? 12-25

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Would eyes be an advantage in a typical lake? What about in a cave with no light? 12-26

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Founder Effect The founder effect is a type of genetic drift that occurs when a new population is established by a few colonizing individuals. – The small colonizing group may have different allele frequencies than the original population. – When the colonizing individuals mate and multiply, their allele frequencies will tend to persist, making the new population different from the parent population.

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Genetic Bottleneck Genetic bottleneck is another form of genetic drift. Occurs when there is a dramatic reduction in population size – Usually due to some chance event like a natural disaster – Could be due to over-hunting by humans The remaining members of the population will mate and pass on their alleles, limiting their genetic diversity. Many endangered species are undergoing genetic bottlenecks.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Bottleneck Demonstration 12-30

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Bottleneck Whooping Crane bee.blogspot.com/2011/02/vermiliontodayco m-whooping-cranes.html bee.blogspot.com/2011/02/vermiliontodayco m-whooping-cranes.html 12-31

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display Barriers to Movement When migration is limited, populations become geographically and reproductively isolated. – Perpetuates the effects of genetic drift caused by founder effect and bottleneck – Limits genetic diversity and generates subspecies

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