1. Chp 20 Generation to generation change in allele frequency
Genes and populations
Chp 20
Generation to generation change in allele frequency

2. Evolution
Populations of living things slowly adapt and change over time
Does not explain origin of the very first living thing

3. Evolution theory is a way to show the connection of all life forms

4. Evolution also explains the variety within a kind

5. Carolus Linnaeus 1707-1778 Father of modern taxonomy (classification)
Binomial nomenclature
genus species
Canis Lupus

6. James Hutton
Gradualism – Profound change is the product of slow, continuous processes
“The present is the key to the past”
Ex. Mountains grow slowly now
so they always grew slowly!

7. Jean Baptiste Lamarck 1744-1829
Evolution through acquired traits
Based on fossils, relics or impressions of dead organisms
Sedimentary rock, ice, tar, amber

8. Charles Darwin 1809-1882 Evolution by natural selection
Also cited fossil evidence
Anticipated that intermediates
would be found
Travelled extensively to
observe diversity of life
Published “origin of species”
In 1859

9. Evolutionary theories
Lamarck VS Darwin

10. Lamarck - Inheritance by acquired characteristics
Individual organisms change.
Ex Giraffes – stretched their necks to get food and passed longer necks on to offspring

11. Darwin – Natural selection
.Survival of the fittest.
The ones best naturally adapted to survive, have more offspring and pass on the traits to those offspring

12. Darwin’s version of giraffes
Some giraffes were born with longer necks and better able to get food. These ones survived and passed longer necks to their offspring

13. Population Genetics Studies the genetic variations within a population
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14. Species
A group of organisms capable of breeding to produce fertile offspring

15. Different species can not reproduce and have offspring that can reproduce

16. Variations
When different species members have differences in characteristics
Ex. Dogs – one species but many varieties

17. Population
A localized group of individuals of the same species

18. Gene pool
All of the genes in a population

19. Why does the dominant trait take over?
Hardy and Weinberg stated the genes in a population will remain stable if under certain conditions

20. Assumptions of Hardy Weinberg
There are no mutations.
No genes transferred (No immigration or emigration)
Mating is random.
The population should be large.
No selection is occurring

21. Hardy-Weinberg theorem
An equation used to identify a
non-evolving population.
Looks at the frequency of each allele
HARDY WEINBERG EQUILIBRIUM = There is no change in gene frequency in a population
p pq + q2= 1

22. Mendel genetics – Apply to alleles in one gametes of one pair
Mate two individuals heterozygous (Bb) for a trait.
25% offspring are homozygous for the dominant allele (BB)
50% are heterozygous like their parents (Bb) and
25% are homozygous for the recessive allele (bb) and express the recessive phenotype

23. populations have random alleles
The frequency of two alleles in an entire population of organisms is unlikely to be exactly the same. Ex. population of hamsters:
A) 80% of all the gametes in the population carry a dominant allele for black coat (B) and
B) 20% carry the recessive allele for gray coat (b).

24. hamsters MENDEL monohybrid cross
Results of random union of the two gametes produced by two individuals, each heterozygous for a given trait. As a result of meiosis, half the gametes produced by each parent with carry allele B; the other half allele b.
RANDOM POP
Results of random union of the gametes produced by an entire population with a gene pool containing 80% B and 20% b.
0.5 B
0.5 b
0.8 B
0.2 b
0.25 BB
0.25 Bb
0.64 BB
0.16 Bb
0.25 bb
0.04 bb

25. Allele frequency P = frequency of dominant allele
q = frequency of recessive allele
Brown eyes vs blue eyes
Brown (B) = P
Blue (b) = q

26. Mind your Ps and Qs
From old English pubs, be careful how many pints and quarts you consume
Also from old typesetters, not mixing up ps and qs

27. Total frequency of alleles in population = 1 THEREFORE
p + q = (dom + res = 1)
q =1 – p (res = 1 – dom)
p = 1 – q (dom = 1 – res)
Ex. R = red r = white there are 20% white flowers in a field
q freq =.2 (20%) white
then p freq = = .8 (80%) red

28. Allele frequency of a dominant and recessive trait
Similar to punett square

29. Ex. Frequency alleles of Red (R) and white (r) flowers
p pq q = 1
Frequency freq freq
of RR of Rr rr
genotype genotype genotype

30. p2 + 2 pq + q2 = 1 Given: 4% of the population = white flowers (rr)
What is the frequency of r? (q)
What is the frequency of R? (p)
What % of pop. = Rr?
q2 = so q = so p = .8
4% rr
2(.8)(.2) = .32 Rr = 32% Rr
64% RR

31. NOT Hardy Weinberg equilibrium
Change of allele frequency in 3 generations

32. 5 agents of evolutionary change
Things that CHANGE equilibrium of gene pool

33. 1) Mutation
Change in DNA code
Mutagen

34. Mutations
The origin of new alleles

35. 2) Gene Flow Migration – Individuals move from one population to next
Bring genes into new population

36. 3) Non-Random Mating
Self fertilization
Inter breeding

37. 4) Genetic drift
A change in frequency due to chance

38. Bottleneck effect Genetic drift due to a reduction in population size
Ex skittles

39. Tsunami bottle neck

40. Founder effect
Genetic drift due to formation of a new colony with organisms with distinctly different phenotypes

41. 5) Natural selection Darwin’s idea Survival of the fittest
The environment influences who passes on their DNA

42. Fitness - ability to pass on traits to offspring
The individuals in a population that are most fit are the ones that survive
Attract mates better
Catch prey better
Hide better from predators

43. Polymorphism – When there are two or more forms of one character
aids natural selection by increasing possible phenotypes

44. Geographic Variation Differences in gene pools between populations
Can aid natural selection

45. Cline
A graded change in a trait over a geographical area

46. Heterozygote advantage
When it is advantageous to be heterozygous
Ex Sickle cell anemia

47. Types of Natural Selection

48. Directional selection
One extreme is better
Ex. length of an anteaters tongue

49. Diversifying selection
Opposite extremes are favored
Ex. White shell or Dark shell

50. Stabilizing selection
The average is best
Ex. Field mouse size

51. Types of natural selection

52. Sexual selection
Picking a mate based on secondary sexual characteristics
EX. Tail of peacock

54. Sexual dimorphism Difference in appearance between males and females
Males tend to be more colorful

55. Males tend to be shorter
Ex. Praying mantis

56. Diamond back terrapins
Males smaller

57. Or just weird to us humans

58. More sexual dimorphism

59. Intrasexual selection
Competition between individuals of same sex
Ex. Rams, elephant seals

60. Fight for Harem

61. Inter sexual selection
(mate Choice)
One sex is choosy about selecting mates
Ex Bower bird makes fancy bower to attract mate