Group Quiz Rules Everyone plays a role. No one gets to sit back and relax! Roles: 1)Name recorder 2) Summarizer for q’s1-5 (if you have 5 people at table) or q’s 1-3 (if you have 6 people at your table) - summarize the answer and make sure everyone agrees on one answer to be written 3) Participation guard- make sure everyone has a say 4) Scribe – record the answer 5) Time keeper- keep your group on task! You have 8 minutes to finish the quiz! 6) Summarizer for q’s 4-5- same job as role # 2.
Clarifying Misconceptions Evolution is not the adaptation of individuals….this process of adaptation occurs through natural selection
Clarifying Misconceptions Evolution is not the adaptation of individuals….this process of adaptation occurs through natural selection Evolution occurs in populations….this word must be in your definition of evolution
Clarifying Misconceptions Evolution is not the adaptation of individuals….this process of adaptation occurs through natural selection Evolution occurs in populations….this word must be in your definition of evolution Natural selection is a process for evolution to occur, and this process includes the adaptation of individuals in a population to the environment
Clarifying Misconceptions Evolution is not the adaptation of individuals….this process of adaptation occurs through natural selection Evolution occurs in populations….this word must be in your definition of evolution Natural selection is a process for evolution to occur, and this process includes the adaptation of individuals in a population to the environment Important components of natural selection: 1)Traits vary among individuals 2)There are more individuals in an environment than can be supported by available resources 3)Certain traits allow individuals to survive and reproduce at higher rates than others with other traits 4)These traits are heritable.
Today’s class structure Quiz 8 minutes, then 3 min to go over Genetics mini review and review on H-W equilibrium Be a leader assignment H-W assumptions lecture HW worksheet in class
Be a leader 1’s, 2’,s and 3’s, unite! Agree with one answer Choose a representative to show the class how to solve this problem You have 6 minutes…go!!!
Be a leader 1) If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous(Ss) for the sickle-cell gene?
Be a leader 2) This is a classic data set on wing coloration in the scarlet tiger moth ( Panaxia dominula ). Coloration in this species had been previously shown to behave as a single-locus, two-allele system with incomplete dominance. Data for 1612 individuals are given below: White-spotted (AA) =1469 Intermediate (Aa) = 138 Little spotting (aa) =5 Calculate the following frequencies: A = ____ a = _____ AA = ________Aa = ________aa = ____________
Be a leader 3) After graduation, you and 19 friends build a raft, sail to a deserted island, and start a new population, totally isolated from the world. Two of your friends carry (that is, are heterozygous for) the recessive cf allele, which in homozygotes causes cystic fibrosis. a) Assuming that the frequency of this allele does not change as the population grows, what will be the instance of cystic fibrosis on your island? b) Cystic fibrosis births on the island is how many times greater than the original mainland. The frequency of births on the mainland is.059%.
The key component for evolution to occur is… Genetic variation!!
Genetic Variation Genetic variation among individuals is caused by differences in genes or other DNA segments Phenotype is the product of inherited genotype and environmental influences Natural selection can only act on variation with a genetic component
Variation Within a Population Both discrete and quantitative characters contribute to variation within a population Discrete characters can be classified on an either-or basis Example: color, shape, presence/absence of a phenotype Quantitative characters vary along a continuum within a population Example: body mass, litter size Discrete: colorQuantitative: size
Sources of Genetic Variation New genes and alleles can arise by mutation or gene duplication Sexual reproduction produces genetic variation through crossing over, independent assortment, and fertilization
Alleles are different variations of a gene Genotypes are combination of alleles that an individual has, One allele came from parent 1, and other came from parent 2
Hardy-Weinberg Principle Allele frequencies of alleles and genotypes in a population will remain constant from generation to generation if all assumptions are met A gene pool that remains constant is said to be in Hardy-Weinberg equilibrium
AA Aa aa Generation 1 ? Generation 2 p 2 + 2pq + q 2 = 1
Practice on your own right now: Write this in your notes. There are 500 cats in a population, which has two alleles, T and t, for a gene that codes for tail length. The table below presents the phenotype of cats with each possible genotype, as well as the number of individuals in the population with each genotype. Assume that this population is in Hardy- Weinberg equilibrium.
Assumptions of Hardy-Weinberg principle Allele frequencies in a population will remain constant if ALL of the following conditions are met: 1.The population is infinitely large 2.Individuals mate randomly 3.No genetic migration and mutation 4.No natural selection 5.No mutation
Three main driving forces that cause changes in allele frequencies Natural selection Genetic drift Gene flow
1) Natural selection Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals without those traits Adapations are inherited traits that enhance organismal survival and reproduction in specific environments Fitness: measure of reproductive success associated with a particular trait
Evolution by natural selection involves both chance and “sorting” New genetic variations arise by chance Beneficial alleles are “sorted” and favored by natural selection Only natural selection consistently results in adaptive evolution Natural selection is the only mechanism that consistently causes adaptive evolution
Figure 23.13 Original population Phenotypes (fur color) Frequency of individuals Original population Evolved population (a) Directional selection (b) Disruptive selection(c) Stabilizing selection
2) Genetic Drift- the reason why large population size is important for Hardy- Weinberg Equilibrium The smaller a sample, the greater the chance of deviation from a predicted result Genetic drift : when chance events cause allele frequencies to fluctuate unpredictably from one generation to the next Genetic drift tends to reduce genetic variation through losses of alleles
Figure 23.9-1 Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 CRCRCRCR CRCRCRCR CRCWCRCW CWCWCWCW CRCRCRCR CRCWCRCW CRCRCRCR CRCWCRCW CRCRCRCR CRCWCRCW
Figure 23.9-2 5 plants leave off- spring Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 CRCRCRCR CRCRCRCR CRCWCRCW CWCWCWCW CRCRCRCR CRCWCRCW CRCRCRCR CRCWCRCW CRCRCRCR CRCWCRCW CRCRCRCR CWCWCWCW CRCWCRCW CRCRCRCR CWCWCWCW CRCWCRCW CWCWCWCW CRCRCRCR CRCWCRCW CRCWCRCW Generation 2 p = 0.5 q = 0.5
Figure 23.9-3 5 plants leave off- spring Generation 1 p (frequency of C R ) = 0.7 q (frequency of C W ) = 0.3 CRCRCRCR CRCRCRCR CRCWCRCW CWCWCWCW CRCRCRCR CRCWCRCW CRCRCRCR CRCWCRCW CRCRCRCR CRCWCRCW CRCRCRCR CWCWCWCW CRCWCRCW CRCRCRCR CWCWCWCW CRCWCRCW CWCWCWCW CRCRCRCR CRCWCRCW CRCWCRCW Generation 2 p = 0.5 q = 0.5 2 plants leave off- spring CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR CRCRCRCR Generation 3 p = 1.0 q = 0.0
The Founder Effect The founder effect occurs when a few individuals become isolated from a larger population. Example: wind blows birds off course to another island Allele frequencies in the small founder population can be different from those in the larger parent population
The Bottleneck Effect The bottleneck effect is a sudden reduction in population size due to a change in the environment, ex: urbanization The resulting gene pool may no longer be reflective of the original population’s gene pool If the population remains small, it may be further affected by genetic drift
Figure 23.10-2 Original population Bottlenecking event
Figure 23.10-3 Original population Bottlenecking event Surviving population Reduction in genetic variation via genetic drift!!!
Case Study: Impact of Genetic Drift on the Greater Prairie Chicken Loss of prairie habitat caused a severe reduction in the population of greater prairie chickens in Illinois The surviving birds had low levels of genetic variation, and only 50% of their eggs hatched
Figure 23.11 Pre-bottleneck (Illinois, 1820) Post-bottleneck (Illinois, 1993) Greater prairie chicken Range of greater prairie chicken (a) Location Population size Number of alleles per locus Percentage of eggs hatched 93 <50 5.2 3.7 5.8 99 96 1,000–25,000 <50 750,000 75,000– 200,000 Nebraska, 1998 (no bottleneck) (b) Kansas, 1998 (no bottleneck) Illinois 1930–1960s 1993
Effects of Genetic Drift: A Summary 1.Genetic drift is significant in small populations 2.Genetic drift causes allele frequencies to change at random 3.Genetic drift can lead to a loss of genetic variation within populations 4.Genetic drift can cause harmful alleles to become fixed
3) Gene Flow Gene flow consists of the movement of alleles among populations Alleles can be transferred through the movement of fertile individuals or gametes (for example, pollen) Gene flow tends to reduce variation among populations over time Gene flow can decrease or increase the fitness of a population