4I. Variation & Gene Pools ______ ____- all genes (dominant and recessive alleles) that are present in a population.Gene Pool4
5Ex. What genes are present in ________SwedenJapanMexico5
6Because members of a population interbreed, they share a common group of genes called a ___________ A gene pool consists of ____________ present in a population, including all the different _________. Remember: alleles code for a gene which determines the phenotype. Genes will have 2 alleles, one given by each parent. The combination of the two alleles on the gene will determine the expressed physical characteristic or phenotype.GENE POOLALL the genesalleles
7II. Sources of Genetic Variation Mutations1. ___________= changes or random errors in DNA (by chance)2. _____ ______Gene flowMigration7
83. ______ ____= random change in allele frequency Genetic Driftaffects small, isolated populations mostEx: Amish8
9Polydactilysm_____________ in the Amish Population9
10Natural selection is NOT the only source of evolutionary change. REMEMBER ! Genetics is controlled by_________________PROBABILITYThe smaller the population . . .the farther the ________results may befrom the ___________ outcomes.actualpredicted
11In a small population random changes in allele frequency based on chance is called _________________ GENETIC DRIFTGenetic drift can occur whena _______ groupof individualscolonizes a_____habitat.smallnew
16Natural selection can affect the distribution of phenotypes in 3 ways: ______________________DIRECTIONAL selectionSTABILIZING selectionDISRUPTIVE selection
171. _________ ________= favors average individuals in a population Stabilizing selectionEx: lizards – large captured easily & small cannot run fast enough
18STABILIZING SELECTION CENTERIndividuals in _____________ of the curvehave higher fitness than individuals ateither endGraph stays in same place but narrows as more organismsin middle are produced.
19EXAMPLE OF STABILIZING SELECTION Human babies born with low birthweight are less likely to survive.Babies born too large have difficulty being born.Average size babies are selected for.
20STABILIZING SELECTION Section 16-2Stabilizing SelectionMale birds withshowier, brightly-colored plumagealso attractpredators, and areless likely to livelong enough tofind a mate.The mostfit, then, is the malebird in the middle--showy, but not tooshowy.Male birds use their plumage to attract mates. Male birds in the population with less brilliant and showy plumage are less likely to attract a mate, while male birds with showy plumage are more likely to attract a mate.KeyLow mortality, high fitnessHigh mortality, low fitnessSelection against both extremes keep curve narrow and in same place.Percentage of PopulationBrightness ofFeather Color
212. ________ ________= favors one of the extreme variations of a trait Directional selectionEx: Anteaters – long tongues are best to get food
22DIRECTIONAL SELECTION KEYLow mortality,high fitnessHigh mortality,low fitnessFood becomes scarce.Individuals at _____________ of the curvehave higher fitness than individuals inmiddle or at other end.Graph shifts as some individuals fail to survive at one endand succeed and reproduce at otherONE END
23EXAMPLE OF DIRECTIONAL SELECTION Beak size varies in a populationBirds with bigger beaks can feedmore easily on harder, thickershelled seeds.Suppose a food shortage causes small and medium size seeds torun low.Birds with bigger beaks would beselected for and increase in numbersin population.
243. ________ _______– favors both extreme variations of a trait Disruptive selectionEx: Limpets – white colored mimic white barnacles & dark colored camouflage on dark rocksno intermediate forms survive
25DISRUPTIVE SELECTION Individuals at _____________ of the curve have higher fitness than individuals in middle.Can cause graph to split into two.Selection creates __________________PHENOTYPESEXTREMESTWO DISTINCT
26EXAMPLE OF DISRUPTIVE SELECTION Suppose bird population lives in areawhere climate change causes mediumsize seeds become scarce while largeand small seeds are still plentiful.Birds with bigger or smaller beakswould have greater fitness and thepopulation may split into TWOGROUPS. One that eats smallseeds and one that eats large seeds.
29I. Formation of SpeciesSPECIES = organisms that ________& ______ to produce ________ _________.Similar gene poollook alikebreedfertileoffspring29
30b. _________ = forming a new species must have isolation Speciationb. _________ = forming a new speciesmust have isolationEx: Galapagos finches isolated from mainland30
31What events lead to the formation of new species? Reproductive Isolation(1) ________ _________:When two members cannot interbreed and produce fertile offspringEach species is now their own separate group31
32Ex: Birds using different songs to attract mates Isolation Mechanisms(2) _________ ________= differ in courtship rituals or don’t respond to mating signalsBehavioral isolationEx: Birds using different songs to attract mates32
33(3) _________ _________= population separated by physical barriers Geographic isolationEx: island formation, river/canyon33
34(4) ________ _______= species reproduce at different times of the year Temporal isolationEx: orchids pollinate on different days34
35EVOLUTION OF POPULATION Evolution as Genetic Change 16–2
36GAPS IN DARWIN’S THINKING: How do heritable traits pass from one generation to the next?How does variation in the population appear?
37When Darwin developed his theory of evolution, he didn’t know how ____________worked.Mendel’s work on ______________ was published during Darwin’s lifetime, but ________________ as important until __________________.HEREDITYinheritance in peasNOT recognizeddecades later
38____________ and ________ TODAY we can understand how evolution works better than Darwin ever could because of our knowledge about____________ and ________genesDNA
39EVOLUTION IN GENETIC TERMS __________________ is any change in the relative frequency of alleles in a populationIf the relative frequency of the B allele in this mouse population changed over time to %, the population is evolving.EVOLUTION
40____________________ on NATURAL SELECTION____________________ onsingle-gene frequencies can lead to changes in ____________________ and thus to EVOLUTONALLELE FREQUENCIESEX: A population of normally brown lizards. Mutations produce new color choices.If red lizards are more visible to predators, they might be less likely to survive.
41can be less common even if it is DOMINANT! In real populations, phenotypic ratios are determined not only by which allele is _____________, but by _______________ of the allele in the populationDOMINANTFREQUENCYPresence of widow’speak in populationcan be less common even if it isDOMINANT!
42The ____________________ is the number of times that an allele occurs in the gene pool compared to the occurrence of other alleles in the gene pool.relative frequencySample Population48% heterozygous black36% homozygous brown16% homozygous blackFrequency of Allelesallele for brown furallele for black fur
43RELATIVE FREQUENCY is often expressed as a __________________. EX: In this population Dominant B allele (black) = 40% Recessive b allele (brown) = 60%percentage
44NOTHING DOMINANT RECESSIVE RELATIVE FREQUENCY has _________ to do with whether an allele is______________ or _____________In this population, the recessive allele is more frequent.DOMINANT RECESSIVE
45Black lizards absorb more heat to warm up faster on cold days so they can move faster to get food and avoid predators. The allele for black may increase in frequency.
46change the __________________ of alleles in population! NOT SEXUAL REPRODUCTION_______________________IS THE MAJOR SOURCE OF VARIATION IN POPULATIONS, but it does _______change the __________________ ofalleles in population!NOTrelative frequencyShuffling a deck of cardscan shuffle to producemany different hands,but doesn’t change thenumber of kings orqueens in the deck.
47GENE SHUFFLING during _________ _____________ _______________ REMEMBER !MEIOSISGENE SHUFFLING during ________________________________________________________Crossing overSegregationIndependent AssortmentRESULT IN GENETIC RECOMBINATION
48Independent assortment ____________________ during__________ of _______ is a lot likeshuffling a deck of cards. There arealways 52 cards, and the _________of you being dealt any one card isalways the same.Anaphase Imeiosisprobability
50During ____________________, there are 23 ___________ “cards” thatcan be “shuffled” and “dealt” in_________ combinations! Also,sometimes the “cards” you are dealtare brand-new and unique due to___________.independent assortmentchromosome8.4 millioncrossing over
51that control that trait. PHENOTYPES The number of _______________ produced for a given trait depends on the number of ______that control that trait.PHENOTYPESGENESEX: Widow’s peakNo widow’s peakSingle gene traits result inonly _______phenotypes.TWO
52_______________ traits are controlled by two or more genes.POLYGENICA bell shaped curve istypical of polygenic traits
53When traits are controlled by _______ than one gene, the effects are more complex. Remember ______________ traits show a bell-curve distributionmorepolygenic
54Chemicals Radiation BIOLOGISTS can now explain how the _____________ that DARWIN saw is produced!A __________ is any change in aa sequence of _______SOURCES OF MUTATIONS: _________________________________________________________________variationmutationDNAMistakes in replicationChemicalsRadiation
55Mutations that change phenotype can affect an organism’s ____________ (ability to survive and reproduce)fitness
56Each time an organism reproduces, it passes its genes on to the nextgeneration.So __________= success in passing on genesFITNESS
57The ___________ of individuals near each other will not be very different, but fitness may vary from one end of curve to the other.FITNESSWhere fitness varies,________________can act!NATURAL SELECTION
58silent Many mutations are ___________ and result in death. Some mutations are ____________ and DON’T affect and organism’s ______________at all.LETHALsilentPHENOTYPEEX: Changing the code from GGA to GGUdoesn’t change theamino acid used
59Individuals may carry alleles in ______________ relative frequencies than in the larger population. The population they “found” will be different from the parent population. . . not throughnatural selectionbut by _________differentchance
60A situation in which allele frequencies change as a result of the migration of a small subgroup of thepopulation = _________________FOUNDER EFFECT