1 / 39

Bio. Exam Rooms Friday 5:00 6:50 PM

Bio. Exam Rooms Friday 5:00 6:50 PM. What is evolution?. Change through time. Decent with modification. Change in the genetic make-up of biological populations through time. How does evolution occur?. This does happen Natural Selection. MUTATION. SEX Fertilization. CROSSOVER

debbiesmith
Download Presentation

Bio. Exam Rooms Friday 5:00 6:50 PM

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Bio. Exam Rooms Friday 5:006:50 PM

  2. What is evolution? Change through time Decent with modification Change in the genetic make-up of biological populations through time

  3. How does evolution occur?

  4. This does happenNatural Selection MUTATION SEX Fertilization CROSSOVER Genetic recombination HEREDITY NEW SPECIES NATURAL SELECTION VARIATION

  5. This doesn’t happen Inheritance of Acquired Characteristics ENVIRONMENT “NEED” USE & DISUSE HEREDITY NEW SPECIES

  6. This doesn’t happenOR DOES IT? ENVIRONMENT “NEED” USE & DISUSE Epigenetics HEREDITY ? NEW SPECIES

  7. POPULATION GENETICS NOW.....

  8. POPULATION GENETICS= • Study of the change in the allele frequency in a population through time • Gene pool = total collection of the alleles of a gene in the population

  9. Rabbit Island • 1000 rabbits = 600 brown & 400 white • 2 alleles & complete dominance Brown (B) dominant White (b) recessive • 3 genotypes BB & Bb= Brown bb = white

  10. Suppose • 500 Homozygous brown rabbits BB = 1000 B alleles • 100 Heterozygous brown rabbits Bb = 100 B alleles 100 b alleles • 400 Homozygous white rabbits bb = 800 b alleles • Total: 1100 B alleles 900 b alleles Or 55% B 45% b

  11. Suppose the Allele Frequency in the Original Colonists was • p= fraction of gene pool with dominant allele. (p= .55) • q = fraction of gene pool with recessive allele. (q= .45) • Total p + q = 1.00 (0.55) + (0.45) = 1.00

  12. Imagine a barrel with 55% brown marbles and 45% white.What are the chances of drawing two B’s from the population at random? • 0.55 • 0.45 • 0.3025 • 0.4950 • None of the above 1

  13. What is the frequency of the white genotype in the next generation?i.e. What are the chances of drawing two b’s from the gene pool if there are 55% brown and 45% white alleles? • 0.55 • 0.45 • 0.3025 • 0.4950 • None of the above 1

  14. What is the frequency of the Bb genotype in the next population? • 0.55 • 0.45 • 0.3025 • 0.4950 • None of the above 45

  15. Hardy-Weinberg Principle • p2 + 2pq + q2 = 1.0 BB Bb bb

  16. HARDY-WEINBERG PRICIPLE Allele frequency & genotype frequency will remain constant from generation to generation if • No natural selection • No differential migration (no gene flow) • No differential mutation • Random mating • Large population (no genetic drift or random genetic changes)

  17. Hardy-Weinberg Principle • p2 + 2pq + q2 = 1.0 • BB Bb bb T h i s d e s c r i b e s t h e s i t u a t i o n W h en t h e r e I s N O e v o l u t I o n

  18. Using the Hardy-Weinberg equation • How many of you can roll your tongues? • It is due to a dominant allele R • She is either RR or Rr • Non-rollers are rr

  19. So 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) • Let us assume that there is no selective advantage to tongue rolling so that the Hardy-Weinberg conditions hold • Now remembering that the gene pool is composed of only R’s & r’s, can you calculate what % of the gene pool is r and what % is R?

  20. If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr)What is the frequency of the allele (r) in the gene pool? • 0.2 • 0.36 • 0.60 • 0.80 • I don’t know how to do this.

  21. Suppose 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr)What is the frequency of non-tongue rollers (rr) in the population? • 0.36 • 0.64 • 0.80 • None of the above • I don’t know how to do this.

  22. If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr)What is the frequency of the allele for tongue rolling (R) in the gene pool? • A) 0.20 • B) 0.36 • C) 0.60 • D) 0.80 • E) I don’t know how to do this

  23. If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr)What is the % of homozygous dominants (RR) in the population? • 4% • 16% • 32% • 35% • None of the above

  24. And if there are 400 students in this room how many are Rr?

  25. ANSWER • If 36% of the class can roll their tongues (RR or Rr) • & 64% can not roll their tongues (rr) Remember p2 + 2pq + q2 RR + (Rr + rR) + rr 4% + 32% + 64% = 100%

  26. And if there are 400 students in this room how many are Rr? • 0.32 x 400 = 128

  27. If a change in allele frequency does occur (i.e. there is evolution), then the rules of the Hardy-Weinberg Principle have been violated.

  28. HARDY-WEINBERG PRICIPLE Allele frequency & genotype frequency will remain constant from generation to generation if • No natural selection • No differential migration (no gene flow) • No differential mutation • Random mating • Large population (no genetic drift or random genetic changes)

  29. Consider the problem of population size • Random changes will be important in small populations (< 500 individuals). Small populations do not have a large number of possible variations in their alleles. 1. “Founder effect”during the founding of new colonies. 2. “Bottleneck effect”because of population crashes. 3. “Genetic drift”in small populations

  30. The Founder Effect 1) Shuffle your deck of cards 2) Deal out 10 cards face down 3) Look at your cards and indicate how many red cards you have with your clicker

  31. The Founder Effect1) Shuffle your deck of cards2) Deal out 10 cards face down3) Look at your cards and indicate how many red cards you have with your clicker • One • Two • Three • Four • Five • Six • Seven • Eight • Nine • Ten

  32. Founder Effect is the loss of genetic variation that occurs when a new population is established by a small number of individuals from a larger population The new population is only a sample of the original population diversity and may be drastically different. e.g. Genetic diversity of Icelanders, & Easter Island natives is much less than the population at large. e.g. Amish population established by only a few colonists and the prevalence of polydactyly is much higher than the original population.

  33. Bottleneck Effect is the loss of genetic variation that occurs when a great decrease in the population size occurs. The new population is only a sample of the original population diversity and may be drastically different. e.g.The frequency of total color blindness among the inhabitants of Pingelap, an island in Micronesia. Around 1775, a typhoon reduced the population of the island to only 20. Among survivors, one of them was heterozygous for color blindness. After few generations, the prevalence of color blindness was 5% of population and 30% as carriers (in the USA, only 0.003% of the population has complete color blindness).

  34. Genetic driftis the change in the frequency of a gene variant (allele) in a population due to random sampling. • Take 10 cards, half red and half black. • Mix thoroughly face down. • Without looking at the faces of the cards, pick out ½ of the cards and return them to the deck. • Count the number of red and black cards remaining and record the numbers. • Simulate reproduction= For each card remaining, add one of the same color. This simulates asexual reproduction. Now you have 10 cards again. • Repeat steps 2—6 for several generations. • Stop when only one color is left (i.e. has become “fixed.”)

  35. Effect of population size on random variation

  36. But the Hardy-Weinberg Rule is seldom in effect “ The most tenacious misconception in biology may be the idea that all processes serve a purpose This idea is so deep-seated that students fail to even consider random processes as responsible for biological patterns” Genetic Drift is a random process and is responsible for many characteristics of populations. It happens in all populations, not just small ones, although the smaller the population the faster and more profound the effect is likely to be.

  37. Now you know how to do it.Don’t you? First, figure out the recessive allele frequency and everything else follows!

  38. Another Problem There are 500 dragons in a population 495 are red and 5 blue Red is the dominant allele with complete dominance. How many dragons in the population carry the blue allele but are red? i.e. How many are Rr ? • 5 • 10 • 18 • 405 • None of the above

  39. GOOD LUCK ON THE EXAM!

More Related