Evolution Change in DNA to favor certain traits over multiple generations Adaptations happen within a single generations Evolution is the result of adding adaptations together Evolution doesn t have a goal Based on previous generations conditions Peppered Moth Very widespread (large sample sizes) China Russia Japan Nepal Europe North America Generally light colored Has an alternative dark coloration expressed by some individuals 2 forms: Light form (typical) Dark form Moths of this species, regardless of color, tend to use light colored, lichen-covered trees as cover Trait characteristic (hair color) Gene segment of DNA Allele a variety of a trait (brown hair or blonde hair) The dark version of the gene is dominant, although rarer in nature AA Aa aa Dark Dark Light This means that light moths which interbreed will always, and only, produce light colored offspring
In normal populations, the light moth group were >99% of the total population Advantage: Camouflage Industrial revolution began in early 1800s, and moth populations shifted beginning around 1850 Soot and pollution began covering all outdoor surfaces, turning them uniformly darker Light moths were now at a disadvantage Total allele shift took about 12 15 years Eventually ~97% of the population was dark Beginning in 1960s, cleaner air was mandated, and the trees began to lightened again Light moths regained a slow advantage, and dark moths eventually were at a disadvantage again Original ratio still has not been restored Natural Selection Follows five processes Organisms make more offspring than will survive Offspring tend to have different phenotypes and some survive better than others Phenotype physical traits Those phenotypes are mostly based on genotypes inherited from the parents Genotype combination of alleles Inheritance of the alleles determines how likely the offspring is to survive and reproduce Individuals with good genes reproduce more, and those alleles become more common in a population Describing Genotypes Homozygous Dominant Two dominant alleles (A A) Dominant version of the gene shows Heterozygous One dominant allele and one recessive allele (A a) Dominant version of the gene shows Homo same Homozygous Recessive Two recessive alleles (a a) Hetero - different Recessive version of the gene shows
Allele Frequency How common a certain allele is compared to all of the alleles in a population Total # of alleles in a population is the number of individuals times two Individuals Alleles 100 200 5 10 15 30 To calculate: # of dominant alleles Double the # of homozygous dominant individuals (AA x 2) Add the # of heterozygous individuals (+ Aa) 2 (#AA) + (#Aa) = # of dominant alleles # of recessive alleles Double the # of homozygous recessive individuals (AA x 2) Add the # of heterozygous individuals (+ Aa) 2 (#aa) + (#Aa) = # of recessive alleles In a population of 50: AA: 35 Total alleles= 100 Aa: 10 A = 2(35) + 10 = 80 aa: 5 a = 2 (5) +10 = 20 In a population of 20: 7 homozygous dominant (AA) 3 heterozygous (Aa) 10 homozygous recessive (aa) Total alleles= 40 A = 2(7) + 3 = 17 a = 2(10) +3 = 23
Calculating Allele Frequency Divide each of the two alleles by the total # of alleles These must add up to 1.0 F A = 17 40 =.43 From the last problem: f A = 17 40 =.43 f a = 23 40 =.57 Vocabulary Test on Friday Trait -characteristic (hair color) Gene Allele -segment of DNA -a variety of a trait (brown hair or blonde hair) Phenotype -physical traits Genotype Homozygous Dominant -combination of alleles -Two dominant alleles (A A); Dominant version of the gene shows Heterozygous -One dominant allele and one recessive allele (A a): Dominant version of the gene shows Homozygous Recessive -Two recessive alleles (a a); Recessive version of the gene shows Genetic drift f a = 23 40 =.57.43 +.57 = 1.0 -random disappearance of alleles when all individuals do not breed Founder effect - Happens after every bottleneck - a reduction in alleles b/c a few individuals are trying to rebuild a large population bottleneck - event that greatly reduces the population size migration - Change in the number of alleles when individuals leave or enter a population Immigration increases genetic diversity Emigration decreases genetic diversity The Hardy-Weinberg Equilibrium A way to estimate allele numbers in a population without knowing if the dominant phenotypes are homozygous or heterozygous Scenario 400 flowers are red (dominant) 200 flowers are yellow (recessive) Red is RR or Rr H-W figures out number of each Yellow is rr 5 assumptions of H-W: No mutations happen Nobody leaves or joins the population
Mating is random No genetic drift happens Natural selection doesn t happen This doesn t happen in nature Other things that lead to evolution: Genetic drift random disappearance of alleles when not all individuals breed Decreases genetic diversity Bottleneck event that greatly reduces the population size Bad for genetic diversity b/c many alleles disappear Founder effect happens after every bottleneck Reduction in alleles b/c a few individuals are trying to rebuild a large population Can also happen with isolation Migration Change in the number of alleles when individuals leave or enter a population Immigration increases genetic diversity Emigration decreases genetic diversity The Hardy-Weinberg Equilibrium p + q = 1 p 2 + 2pq + q 2 = 1 p = frequency of dominant allele (f A ) q = frequency of recessive allele (f a )
Example: p 2 = frequency of homozygous dominant genotype (A A) 2pq = frequency of heterozygous genotype (A a) q 2 = frequency of homozygous recessive genotype (a a) Population: 100 Red (R) = 75 White (r) = 25 How many red are heterozygous? 100.5 = 50 p = frequency of dominant allele (f A ) p + q = 1 p +.5 = 1 p =.5 q = frequency of recessive allele (f a ).5 p 2 = frequency of homozygous dominant genotype (A A).5 2 =.25 2pq = frequency of heterozygous genotype (A a) 2 p q 2.5.5 =.5 q 2 = frequency of homozygous recessive genotype (a a).25 Example: p + q = 1 p 2 + 2pq + q 2 = 1 Population: 150 Red (R) = 100 White (r) = 50 How many red are heterozygous? 150.49 = 73.5 p = frequency of dominant allele (f A ) p + q = 1 p +.57 = 1 p =.43 q = frequency of recessive allele (f a ).57 p 2 = frequency of homozygous dominant genotype (A A).43 2 =.18 2pq = frequency of heterozygous genotype (A a) 2 p q 2.18.33 =.49 q 2 = frequency of homozygous recessive genotype (a a).33
Example: Population: 700 Red (R) = 480 White (r) = 220 How many red are homozygous dominant? 700.19 = 133 p = frequency of dominant allele (f A ) 1 -.56 =.44 q = frequency of recessive allele (f a ). 31 =.56 p 2 = frequency of homozygous dominant genotype (A A).44 2 =.19 2pq = frequency of heterozygous genotype (A a) 2.44.56 =.49 q 2 = frequency of homozygous recessive genotype (a a) 220 700 =.31 1. Start with finding q 2 # of homozygous recessive # in population 2. Find q 2 to get q 3. 1 q = p 4. P 2 5. 2 p q Example: Population: 300 Red (R): 174 White (r): 42% of 300 = 126 How many red are heterozygous? 300.46 = 138 p = frequency of dominant allele (f A ) 1 -.65 =.35 q = frequency of recessive allele (f a ). 42 =.65 p 2 = frequency of homozygous dominant genotype (A A).35 2 =.12 2pq = frequency of heterozygous genotype (A a) 2.35.65 =.46 q 2 = frequency of homozygous recessive genotype (a a) 126 300 =.42
Example: In a population of 750 tortoises, 65% have a low-domes shell and the rest have a high-domed shell (the dominant trait). Approximately how many of them should be heterozygous for the trait? Population: 750 Dominant Phenotype: Low-domed 487.5 Recessive Phenotype: High-domed 262.5 3 p = frequency of dominant allele (f A ) 1 - q = p.19 2 q = frequency of recessive allele (f a ) q 2 = q.81 4 p 2 = frequency of homozygous dominant genotype (A A) p 2.04 5 2pq = frequency of heterozygous genotype (A a) 2 p q.31 1 q 2 = frequency of homozygous recessive genotype (a a) #aa population.65 How many are homozygous dominant? Population p 2 How many are heterozygous? Population 2pq 750.31 = 233 Speciation Formation of new species through evolution Species two organisms are the same species if they produce offspring that can also reproduce Species A Species B Offspring (Can it reproduce?) Reproductive Isolation Prezygotic isolation prevents different species from reproducing before the zygote is formed Ecological Isolation Two species reproduce in different parts of the same habitat Example: one species reproduces in a pond, the other in the stream leading to the pond. Cannot reproduce.
Temporal Isolation Two species breed at different times Example: one breeds in Fall, the other in Spring. Example: one breeds at night, the other during the day. Behavioral Isolation Breeding rituals don t cross between species Mechanical Isolation Reproductive parts are not compatible Prevention of Gamete Fusion Sperm and egg chemically incompatible Gamete sperm or egg cell Postzygotic after fertilization Developmental Isolation The fertilized egg does not develop Hybrid Inviability Adult hybrid can t survive nature Hybrid Sterility Healthy adult hybrid can t reproduce Hybrid Made from two different species Vocabulary List Geographic isolation Ecological isolation Behavioral isolation Temporal isolation Developmental isolation Hybrid Inviability Hybrid sterility Gamete Zygote Prezygotic isolation Postzygotic isolation Homologous structures Vestigial structures Analogous structures Cladogram Gradualism Punctuated equilibrium
Evidence for Evolution Most evidence can be seen in the fossil record Fossils show anatomy but they don t show genetics Organisms with similar anatomy may be related but not necessarily Common ancestor A species that two existing species have in common as an ancestor; both species descended from a common ancestor. Common ancestors have similar features to all species that come after it Homologous Structures Anatomical structures that is the same between two related species which the common ancestor had Example: Human arm and a whale fin Analogous Structure Two structures on different species that have a similar function but they had no common ancestor Example: Human arm and a fin of a fish Analogous structures developed separately from each other but for a similar purpose Vestigial Structure Organ or structure no longer used by the organism. It stopped functioning after evolution made it unnecessary. Example: human appendix Tracing Evolution Paths Gradualism Series of small changes over a long period of time leading to a new species Punctuated Equilibrium Long periods of no change or very little change followed by short periods of major change
Phylogeny The evolutionary development or history of a species or group of organisms Evolution and common ancestors are shown on two kinds of diagrams: cladogram or phylogenic tree Cladogram Shows relationships between species and characteristics that divided them Phylogenetic tree Same as cladogram but shows relative time across the bottom Long line long time Short line short time Species 1 is most related to species 2, and least related to species 13