Changes By Chance

1. Changes By Chance Working Definitions

2. Peppered Moth England Prior to the Industrial Revolution in England (pre-1740), the peppered moth was found almost always in its light body colored with black spots. The mothwould spend daylight hours on trees covered with light colored lichen. (Since they blended in with the lichen on the trees, they had perfect camouflage against predatory birds.) There were a few dark colored moths in the population, but their occurrence was rare.

3. The body color of moths is determined by a single gene; the dark version (allele) is dominant (A) and the light allele (a) is recessive.

4. Prior to the Industrial Revolution, the frequency for the light colored moths was higher than the frequency of the dark colored moths.

5. By 1819, the proportion of dark moths increased in the population significantly. Researchers found that the pollution caused by sulfur dioxide from factories was killing the light colored lichens on the trees. (sulfur dioxide is a by-product of coal burning during the Industrial Revolution). Without the light colored background of the trees to protect them from the predatory birds, the light colored moths (aa) were more visible and lost their selective advantage to the dark colored moths

6. By 1848, the dark colored moths ( Aa and AA) had increased from 1% to 90% . The dark colored trees (without the light lichen) served to protect these moths. Now the dark allele (A) could survive in the population. The Hardy-Weinberg equations can be used to illustrate these allele and genotype frequency changes

7. Natural Selection • Not due to human manipulation • Differences in ability to adapt to changes in environmental conditions • Unequal success rates in reproduction • “Survival of the Fittest” = ability to produce viable young

8. Darwin’s Observations and Conclusions • Reproductive capacity of populations is designed • to increase numbers through successive generations • 2. No population can reproduce indefinitely because of limits • Space, food, resources • 3. Infer: Competition for dwindling resources • 4.Individuals share a pool of heritable traits coded for in DNA • 5. Mutations are a source of differentiation in • phenotypic details • 6. Infer: Some phenotypes survive and reproduce • Fitness is the success that an individual has in contributing its • genes to the next generation, alleles for favorable phenotypes • increase in frequency • 7. Conclusions: natural selection and agents of selection

9. Natural Selection Darwin

10. Antibiotic Resistance

11. Tongue Rolling

12. The i’iwi is a songbird with a long, down-curved beak that is native to Hawaii. During the 1800’s, researchers documented that i’iwi fed almost exclusively on nectar from lobelia flowers, which have long, deeply curved tubes. But by 1900, most of the lobelias on Hawaii had gone extinct. Today, i’iwi feed primarily on flowers where nectar is at the base of extremely short tubes. Researchers measured the lengths of beaks on museum specimens collected in the 1800s versus individuals living today. If i’iwis have undergone natural selection in response to changes in their food sources, predict what the data from the study look like.

13. Malaria and Sickle Cell Anemia Cholera and Cystic Fibrosis

14. The Hardy Weinberg Equilibrium Model The biological sciences define evolution as the sum total of the genetically inherited changes in the individuals who are the members of a population's gene pool.  It is clear that the effects of evolution are felt by individuals, but it is the population as a whole that actually evolves.  Evolution is a change in frequencies of alleles in the gene pool of a population. 

15. Let us assume that there is a trait that is determined by the inheritance of a gene with two alleles--B and b.  If the population’s parent generation has 92% B and 8% b and the population’s offspring have 50% B and 50% b, evolution has occurred between the generations.  The entire population's gene pool has evolved in the direction of a higher frequency of the b allele— it was not just those individuals who inherited the b allele that evolved.

16. This definition of evolution was developed as a result of independent work in the early 20th century by Godfrey Hardy,an English mathematician, and Wilhelm Weinberg,a German physician.

17. Evolution will NOT occur in a population if seven conditions are met: 1.  mutation is not occurring2.  natural selection is not occurring3.  the population is infinitely large4.  all members of the population breed5.  all mating is totally random6.  everyone produces the same number of offspring7.  there is no migration in or out of the population If no mechanisms of evolution are acting on a population, evolution will not occur—the gene pool frequencies will remain unchanged. 

18. Hardy and Weinberg went on to develop a simple equation that can be used to discover the probable genotype frequencies in a population and to track their changes from one generation to another.  This has become known as the Hardy-Weinberg equilibrium equation.  In this equation (p+q = 1),p = frequency of the dominant allele q = frequency of the recessive allele for a trait controlled by a pair of alleles (A and a).   In other words, p equals all of the alleles in individuals who are homozygous dominant (AA) and half of the alleles in people who are heterozygous (Aa) for this trait in a population.  In mathematical terms, this is p = AA + ½Aa

19. Likewise, q equals all of the alleles in individuals who are homozygous recessive (aa) and the other half of the alleles in people who are heterozygous (Aa). q = aa + ½Aa Because there are only two alleles in this case, the frequency of one plus the frequency of the other must equal 100%, which is to say p + q = 1

20. Since this is logically true,then the following must also be correct: p = 1 – q There were only a few short steps for Hardy and Weinberg to realize that the chances of all possible combinations of alleles occurring randomly is (p + q)² = 1 or more simply p² + 2pq + q² = 1

21. p² + 2pq + q² = 1 In this equation, p² = predicted frequency of homozygous dominant (AA) people in a population 2pq is the predicted frequency of heterozygous (Aa) people q² is the predicted frequency of homozygous recessive (aa) people. 

22. A (p) a (q) A (p) AA (p2) Aa (pq) aa (q2) a (q) Aa (pq)