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Chapter 2 Genetics and Ecology

Chapter 2 Genetics and Ecology. © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458. Outline. Species occurrence due to evolutionary past. Mutations and chromosomal rearrangements result in a wide variety of species on earth. Outline.

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Chapter 2 Genetics and Ecology

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  1. Chapter 2Genetics and Ecology © 2002 by Prentice Hall, Inc. Upper Saddle River, NJ 07458

  2. Chapt. 02 Outline • Species occurrence due to evolutionary past. • Mutations and chromosomal rearrangements result in a wide variety of species on earth.

  3. Chapt. 02 Outline • Genetic variability can be measured by allozymes or DNA sequencing. • Mechanisms for reductions in genetic variability in populations.

  4. Chapt. 02 Evolutionary History • Importance of evolutionary ecology to the discipline • Example: Control of penguins in the Southern Hemisphere vs. their absence in Northern Hemisphere.

  5. Chapt. 02 Evolutionary History • Example: Control of penguins in the Southern Hemisphere vs. their absence in Northern Hemisphere. (cont.) • Penguins evolved in the Southern Hemisphere.

  6. Chapt. 02 Evolutionary History • Example: Control of penguins(cont.). • Unable to migrate to Northern Hemisphere

  7. Chapt. 02 Evolutionary History • South America, Africa, and Australia • Similar climates (Tropical to temperate)

  8. Chapt. 02 Evolutionary History • Characterized by different inhabitants. • South America: Ex. Sloths, anteaters, armadillos, and monkeys with prehensile tails. • Africa: Ex. Antelopes, zebras, giraffes, lions, baboons, okapi, and aardvark.

  9. Chapt. 02 Evolutionary History • Characterized by different inhabitants (cont.). • Australia: Ex. No native placental mammals except bats, variety of marsupials, egg-laying montremes, duck-billed platypus, and the echidna. • Best explanation of differences: Evolution.

  10. Chapt. 02 Genetic Mutation • Increase in number of species is primarily due to mutation. • Two types of mutation • Gene or point mutation • Chromosome mutation

  11. Chapt. 02 Genetic Mutation • Point mutation • Results from a misprint in DNA copying • Example (Figure 2.1)

  12. Chapt. 02 Direction of transcription AGA CGG DNA TGA TTT GCA ACU RNA UCU GCC AAA CGU Protein Ser Thr Ala Lys Arg Frameshift: Insert T Transition A-G ATG ACG GTT TGC A.. GGA DNA TTT GCA DNA AGT TGA CGG UGC CAA ACG UAC CCU RNA RNA UCA ACU GCC AAA CGU Thr Tyr Glu Ser Cys Pro Protein Ala Thr Lys Arg Protein ?

  13. Chapt. 02 Genetic Mutation • Point mutation (cont.). • Most changes are caused by frameshift mutations • An addition or deletion in the amino-acid sequence usually leads to drastic and often fatal mutations

  14. Chapt. 02 Genetic Mutation • Chromosome mutation • Four types: deletion, duplications, inversions, and translocation • Order of genes is affected (Figure 2.2).

  15. Chapt. 02 Original Breakage Altered A B C D E F G H A B C D E F G H A B C D E F H Deletion Eliminated A B C D E F G H A B C D E F G G H Duplication From another chromosome G E A B G F E D C H F D Inversion G C H A B F G H A B C D E T U V A B C D E F G H A B C D E Translocation O P Q R S T U V O P Q R S T U V O P Q R S F G H

  16. Chapt. 02 Genetic Mutation • Chromosome mutation (cont.). • Deletion • Simple loss of part of a chromosome • Most common source of new genes • Often lethal

  17. Chapt. 02 Genetic Mutation • Chromosome mutation (cont.). • Duplication • Arises from chromosomes not being perfectly aligned during crossing over. • Results in one chromosome being deficient and the other one with duplication of genes.

  18. Chapt. 02 Genetic Mutation • Duplication (cont.). • May have advantages due to increased enzyme production. • Inversion • Occurs when a chromosome breaks in two places. When the segment between the two breaks refuses, it does so in reverse order.

  19. Chapt. 02 Genetic Mutation • Inversion (cont.). • Occurs during prophase.

  20. Chapt. 02 Measuring Genetic Variability • Genetic diversity is essential to the breeding success of most populations. • Two individuals with the same form of enzyme are genetically identical at that locus.

  21. Chapt. 02 Measuring Genetic Variability • Variations in gene loci are found through searching for variations in the enzymes (allozymes). • Gel electrophoresis: Technique for determining differences in allozymes.

  22. Chapt. 02 Measuring Genetic Variability • Example of Gel electrophoresis: Figure 2.3.

  23. Chapt. 02 Gene Sequencing • Another method for assessing variations is the sequence of DNA. • Made possible through the polymerase chain reaction (PCR) technique.

  24. Chapt. 02 Gene Sequencing • Made possible through the polymerase (cont.). • Makes millions of copies of a particular region of DNA, thereby amplifying even minute amounts of DNA.

  25. Chapt. 02 Gene Sequencing • Made possible through the polymerase (cont.). • Important uses in conservation biology, and rare and endangered species.

  26. Chapt. 02 Gene Sequencing • Accelerated through human-made radiation, UV light, or other mutagens.

  27. Chapt. 02 Mutations • Rate of occurrence: one per gene locus in every 100,000 sex cells. • Only one out of 1,000 mutations may be beneficial.

  28. Chapt. 02 Mutations • Estimated that only 500 mutations would be expected to transform one species into another. • Rate of mutation is not the chief factor limiting the supply of variability.

  29. Chapt. 02 Mutations • Variability is mainly limited by gene recombination and the structural patterns of chromosomes.

  30. Chapt. 02 Genetic Diversity and Population Size • Function of population size • Four factors: inbreeding, genetic drift, and neighborhoods.

  31. Chapt. 02 Inbreeding Depression • Mating among close relatives. • Reduced survivorship (Figure 2.4).

  32. Chapt. 02 60 Non-productive matings 50 Mortality from birth to four weeks 40 Percent 30 20 10 0 1 2 3 4 5 6 Years

  33. Chapt. 02 Inbreeding Depression • Various types of inbreeding (Figure 2.5)

  34. Chapt. 02 1.0 0.8 C 0.6 B Fraction of initial genetic variation 0.4 A 0.2 15 20 0 10 5 Generations

  35. Chapt. 02 Inbreeding Depression • Effects of inbreeding on juvenile mortality (fig. 2.6)

  36. Chapt. 02 Saddle back tamarin 70 Ungulates Primates 60 Small Animals 50 Macaque % Juvenile mortality- outbred 40 Chimpanzee Lemur 30 Giraffe 20 Eld’s deer Indian elephant Rat 10 Spider monkey Oryx Mandrill Mouse 0 100 80 20 40 60 % Juvenile mortality-inbred

  37. Chapt. 02 Inbreeding Depression • Effects of inbreeding on small populations (Figure 2.7).

  38. Chapt. 02 Inbreeding Depression • Example of inbreeding: Greater Prairie Chicken (Figures 2.8 and 2.9).

  39. Chapt. 02 Eggs hatched 100 200 75 150 Prairie chicken cocks Eggs hatched (%) 50 100 Number of prairie chicken cocks 25 50 10 0 1973 1980 1990 Year

  40. Chapt. 02 Inbreeding Depression • Example of inbreeding and relation to extinction: Glanville fritillary butterfly (Figure 2.10)

  41. Chapt. 02 1.0 N=1000 0.9 0.8 N=300 0.7 0.6 N=100 0.5 Fraction of initial genetic variation N=20 0.4 0.3 0.2 0.1 200 400 300 100 500 0 Generations

  42. Chapt. 02 Genetic Drift • Probability of the failure to mate • Loss of possible rare gene • Loss of genetic information for subsequent generations resulting in a loss of genetic diversity.

  43. Chapt. 02 Genetic Drift • Probability of the failure to mate • Small populations more susceptible to drift. • The rate of loss of original diversity over time is approximately

  44. Chapt. 02 Genetic Drift • Probability of the failure to mate • equal to 1/2N per generation. • Example: • 1. N = 500 then 1/2N = 0.001 or 0.1% genetic diversity lost per generation.

  45. Chapt. 02 Genetic Drift • Probability of the failure to mate • equal to 1/2N per generation. • Example: • N = 50 then 1/2N = 0.01 or 1% genetic diversity lost per generation.

  46. Chapt. 02 Genetic Drift • Probability of the failure to mate • Example: (cont.). • Over 20 generations, the population of 500 will still retain 98% of the original variation, but the population of 50 will only retain 81.79%.

  47. Chapt. 02 Genetic Drift • Probability of the failure to mate • Example: (cont.). • 50/500 Rule: Need 50 individuals to prevent excess inbreeding and 500 is the critical size to prevent genetic drift.

  48. Chapt. 02 Genetic Drift • Effects of immigration on genetic drift (Figures 2.11 and 2.12). Often immigration of only one or two individuals into a population can counteract genetic drift

  49. Chapt. 02 Number of immigrants per generation 100 5 2 90 1 Percentage of initial genetic variation remaining 80 0.5 70 0.1 60 None 50 10 20 30 40 50 60 70 80 90 100 Generation

  50. Chapt. 02 100 N = 101 or more 80 N = 51-100 N =16-30 60 Percentage of populations persisting N = 31-50 40 N = 15 or less 20 0 10 20 30 40 50 Time (years)

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