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Unformatted text preview: 1/17/2008 Announcements
2:45 pm Wednesday, Jennings 251 Need acceptable written documentation of absence Must be made up the week following the quiz If you make an appointment with Adrea Rodriguez (head TA) for an alternate time and default without letting her know, you will receive a 0 on the quiz So, what's all this natural selection stuff about? Genotype: Natural selection
1) Individuals within a species show genetic variation of heritable traits 2) Overproduction of offspring 3) Survival and reproduction are NOT random
i. ii. iii. Your actual genetic make-up Your genetic potential Phenotype:
What you look like Expression of your genes Result of the interaction between your y genotype and environment Differential reproductive success dependent upon existing environmental conditions Individuals with favorable genetic variations survive and reproduce, or reproduce most These are naturally selected by prevailing environmental (biological, chemical, physical) conditions Alleles alternative forms of genes Allele frequency
The occurrence of a particular allele in a population Frequency of allele A = 0.7 A real world example: Microevolution Microevolution of beak shape and size in Galapagos Finches
14 species Little difference in size and coloration Beak size and shape varies greatly Reflect feeding habit differences Darwin's Finches 1 1/17/2008 Sources of variation in beak shape
Feeding habits - nutritional differences Injuries and accidents Genetic differences among individuals can affect beak size of offspring
Heritable trait A real world example: Beak size in Galapagos Finches
Individual variation in beak size exists within populations Some of this variation is heritable Many offspring do not survive to reproduce Survival and reproduction are not random 3030-year study of finches on island named Daphne Major
Rosemary and Peter Grant All finches (about 1300) on small island Daphne Major marked and measured (1970) Survival to reproduction measured 1977 drought year
Only 24 mm rainfall (mean = 130 mm) 84% mortality of Medium Ground Finches Beaks of surviving finches 6% deeper Beaks of offspring 4-5% deeper 4- Are survival and reproduction random for finches?
Seed supply and size moisture dependent Drought years large, tough seeds Wet years small, soft seeds Large Tribulus seeds abundant during drought During drought, birds with larger beaks survived better than those with small beaks Later drought years
1980 - 19% mortality 1982 - 25% mortality Did evolution occur?
Heritable variation in beak depth existed in finch population before selection Selective event - drought Large b k f L beaks favored d Changes in average beak size a response to selection pressure Change in allele frequency (microevolution) occurred in the population 2 1/17/2008 A real world example: Development of insecticide resistance in insects Spray crops with insecticide to kill insect pests Resistant individuals survive, reproduce Additional applications will be less effective, select further for resistance Individuals best adapted to the prevailing environmental conditions will be more successful in producing offspring that survive ff i th t i Darwin's "Descent with (genetic) modification" Fitness (in the evolutionary sense):
Not the strongest Not the smartest Contribution of an individual to the gene pool of the next generation, generation, relative to that of other individuals (most adaptive individuals) Evolutionary or Darwinian fitness is: NOT Two useful definitions:
Population: individuals of a single species living close enough to each other for interbreeding to occur Gene Pool: All the genes for a given trait in that population A more general example... A model, if you will 3 1/17/2008 A population of mice in an area of mixed grassland and forest
Light color blends with grasses Dark color blends with the forest floor What might happen if the area gradually became all forest? And what might happen if a predator focused on the most common color morph? And what if some factor(s) favored the most common morph? Loss of grassland Loss of dense forest Stabilizing selection in human birth weight
Percent of population t 100 70 50
Percent mo ortality 15 30 20 10 10 5 By acting on individuals, individuals, natural selection causes changes in populations i.e., populations evolve (allele frequencies change) This is evolution by means of natural selection (aka Darwin stuff) 5 3 2 1 2 3 4 5 6 7 8 9 10 11 Birth weight (pounds)
Fig. 17-9, p.273 4 1/17/2008 Can the gene pool of a population or species change over time because of factors other than natural selection? l ti ? YES! Random chance and/or nonnonrandom mating can change the gene pool of a population Especially small populations This is called Genetic Drift Population decimated (e.g., drought, fire) Regrows from a few survivors Subsequent population may have different and/or more restricted gene pool (Genetic Bottleneck) Population regrows from a few colonizing organisms: Founder Effect An example of a Genetic Bottleneck and Founder Effect: the Cheetah House sparrows introduced to NA in 1852 Populations have evolved different characteristics Large sparrows in colder environments Change in allele frequencies over time to adapt to different environments - microevolution 5 1/17/2008 So, now you understand natural selection as a force for evolution. Why should you care about it? You'll find out when we discuss: AIDS Genetic diseases Biotech foods Drug resistance Announcements
Newspaper articles to be read for quiz: PLEASE NOTE THAT FIRST TWO ARTICLES WERE DISCUSSED IN LECTURE 3
"Tiny Specks of Misery, Both Vile and Useful" NYT, 8 Jan 08 "Deadly pest lurks in forest" (in PowerPoint) "Don't trust your daughter with a teenage allosaur" Toronto Globe and Mail, 15 Jan 08 "Scientists around world in race to create artificial life" (blog article) What's news?
"Tiny Specks of Misery, Both Vile and Useful" NYT, 8 Jan 08 Viruses
Noroviruses (stomach) Rhino a d co o a virusus (co o and corona usus (common co d) o cold) Herpes (cold sore) Infectious parasitic agents pass through microfilters that would trap bacteria Contain RNA or DNA with instructions for making more viruses How a virus works
Glycoproteins on virus envelope bind to specific receptors on host cell membrane Virus enters cell, viral genome duplicates d directs host ll d li t and di t h t cell protein synthesis machinery to synthesize virus components Many viruses repackaged, bud from host cell, infect other cells These viruses do not always kill the host cell What's news?
"Tiny Specks of Misery, Both Vile and Useful" NYT, 8 Jan 08 Encased in protein capsids with correct structure to bind to specific cells Thought to have evolved with living cells Found everywhere but very short-lived shortoutside of host Straddle border of life and non-life nonViral elements are a large part of our genetic material 6 1/17/2008 What's news?
"Tiny Specks of Misery, Both Vile and Useful" NYT, 8 Jan 08 What's news?
1) "Deadly pest lurks in forest", Toronto Globe and Mail, 6/7/05 Comparing human genetic code to viruses, base for base humans are over 50% viral Viral elements initially dismissed as "junk junk DNA" However, some scientists suggest that viral DNA is critical for our immune system to adapt so rapidly to viral infections "Viral infections have shaped the nature of the human immune system" What's news? Deadly pest lurks in forests (1)
Emerald ash borer beetle Asian pest imported to Detroit on wood crates "One has to "O h t assume at thi stage that t this t th t destruction of the ash is quite possible" "there are only two types of ash trees: dead and dying" "girdles" ash trees primary tree killer 12 million dead ash trees (and counting) 7 1/17/2008 Buprestidae: Metallic Wood-Boring Beetles; Flatheaded Borers Signs of EAB: larval galleries just under the bark
Serpentine, frassfilled galleries. EAB adult EAB Larva
Ken Chamberlain & Dan Herms, Ohio State University / OARDC Symptoms of EAB: dieback and decline
Epicormic branching Deadly pest lurks in forests (2)
Economic and ecological impacts Ash comprise 20-60% of trees in 20woodlots Control program b i d C t l being developed l d
Quarantine ash tree nursery stock and wood products, fire wood (all species) "Firebreak" 3-4 mile wide, 100 mile long zone all ash trees will be razed Thinning canopy Suckering from roots Could be as devastating as Dutch Elm disease Quiz will cover material up to and including the previous slide 8 ...
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