1. How Populations
Evolve

2. CHARACTERISTICS OF LIFE
GROUPS OF ORGANISMS (POPULATIONS) SHOW VARIATIONS & EVOLVE, OR CHANGE,
TO ADAPT TO THEIR ENVIRONMENT

3. Idea of populations changing or evolving was first proposed by Charles Darwin in 1859 in his book On the Origin of Species by Means of Natural Selection and was counter to the generally accepted idea of Fixed Species.

4. Idea of Fixed Species = takes a literal interpretation of the book of Genesis which states that species were created and never changed.

5. For centuries, since at least the time of Aristotle (4th Century BC), people (including scientists) believed that simple living organisms could come into being by spontaneous generation. This was the idea that non-living objects can give rise to living organisms.
Observation: Every year in the spring, the Nile River flooded, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times.
Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs.
Interesting recipe for bees: Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse.

6. Darwin made two new, main points in The Origin of Species.
1) Modern species came from a succession of ancestors through a process of “descent with modification” or evolution.
2) Evolution occurs through a process called natural selection.

7. Natural Selection
Idea that nature, or the environment, will select the changes that occur in a population over many generations by favoring those heritable traits that are best suited to that environment.
The result of natural selection is evolutionary adaptation, or an increase in the frequency of traits best suited for the environment.

10. Pattern?

11. Darwin’s Key Observations
1) Overproduction: More organisms are born than will survive to reproduce.
This creates a COMPETITION because individuals must compete for limited resources.
Any competition has winners and losers.

12. Darwin’s Key Observations
2) Individual Variation: Members of a population show variations, which can be inherited from the parents.
Some individuals have advantageous traits or adaptations to help them compete.
Adaptation = a genetically determined characteristic that increases an organism’s ability to survive and reproduce in its environment.

13. These adaptations can be:
Behavioral = actions, activities
Morphological = shape, form, structure
Physiological = function, or internal activities

14. Adaptation?

15. Darwin’s Inference from His Observations
Differential Reproductive Success
or Natural Selection
The survivors, with the adaptations, will live to reproduce & pass on these adaptations (DNA) to their offspring, more often than those without the adaptations.

16. which equals evolution
Eventually the population will have more individuals with these adaptations which equals a change in the population,
which equals evolution

18. Survival of the Fittest

19. Survival of the Fittest = REPRODUCTIVE FITNESS

20. Sexual reproduction = produce sex cells or gametes, requires two parents
Eggs and Sperm are gametes
Each gamete has one half set of DNA or chromosomes
Fertilization unites the two gametes and creates a zygote with a full set of chromosomes

21. Asexual Reproduction = no sex cells or gametes produced, only requires one parent
Bacteria = binary fission
Yeast = budding

22. Plants = vegetative reproduction
Includes; rhizomes (underground stems)
Runners or stolons (e.g. strawberries, grasses)
Suckering (shoots that arise from existing root system)
Tubers (e.g. potatoes)
Bulbs (e.g. onions, tulips)

23. Many examples of asexual reproduction, that form clones.
A clone is a population created asexually from one parent or founder, where all individuals are genetically identical.

24. Populations show variations
Source of variations for;
Asexual Reproduction
= mutations, which are changes in DNA not done on purpose
Sexual Reproduction
= mutations & new combinations from fertilization

25. The Modern Synthesis: Darwinism Meets Genetics
The modern synthesis is the combining of
Genetics with Evolutionary Biology
Genetics is the study of DNA and how it produces traits in organisms

26. Gene = A segment of DNA = A sequence of nucleotides
= A portion of the DNA that is the instructions to build a specific protein
= A portion of the DNA that produces a specific trait

28. Genome
Genome = a complete set of an organism’s genes; an organism’s genetic material

29. Genotype
Genotype = The genetic makeup of an organism; the type of genes an organism has in its cells

30. Alleles Allele = a possible form of a gene
Dominant Allele = always expressed
symbol is a capital letter, like “R”
Recessive allele = expression masked by dominant allele
symbol is a lower case letter, like “r”

31. Cells get TWO copies of each different gene
What are the possible genotypes for a gene
with only one recessive & one dominant allele?
RR = Homozygous dominant
rr = Homozygous recessive
Rr = Heterozygous

32. Gene Pool
Gene Pool = all alleles ( possible forms of genes) in all the individuals making up a population
The Gene Pool is the reservoir from which the next generation draws its genes

33. Gene Pool
If only one allele exists for a loci in a population, that allele is said to be fixed in the gene pool, so all individuals would be homozygous.
Each allele has a frequency in a population.

34. Why is the following statement incorrect? “Pesticides have created
pesticide resistance in insects”

35. Analyzing Gene Pools
Imagine a population of wildflowers with two varieties (called morphs),
one red and one white.
Allele for red flowers = R
Allele for white flowers = r
If we know that 70% or 0.70 of all genes in the population are “R” then what percent of all the genes in the population are “r”?

36. If we let p equal the frequency of the dominant allele (R) in a population of wildflowers and q the frequency of the recessive allele (r), then what would p plus q equal?
p q = 1
So, if you know the frequency of one allele you can subtract it from 1 to get the frequency of the other allele.

37. Remember that each body cell has two copies of each gene (RR, Rr, rr)
Each sex cell or gamete only has ½ the DNA of each parent so it only has one copy of each gene (R or r)
What copy of the gene for color would a flower with a homozygous dominant genotype donate to its egg?
What would a heterozygous flower donate?

38. RR RR Rr RR Rr Suppose the following five genotypes
represent an entire population of flowers
RR RR Rr RR Rr
What is p?
What is q?
What is the chance the pollen will have an R ?
What chance for an egg?
What is the chance the egg will have an r ?

40. Hardy-Weinberg formula
p pq + q2 = 1
p2 = frequency of homozygous dominant
2pq = frequency of heterozygous
q2 = frequency of homozygous recessive

42. Phenylketonuria (PKU) = inherited inability to break down the amino
acid phenylalanine

43. Phenylketonuria (PKU)
Untreated it causes mental retardation
Occurs in about one out of 10,000 babies born in the U.S.
Newborns routinely tested for PKU and treated with strict diet
PKU is caused by a recessive allele

44. Phenylketonuria (PKU)
Genotype of RR = Phenotype?
Phenotype = Normal
Genotype of Rr = Phenotype?
Normal, but “carrier” of allele for PKU
Genotype of rr = Phenotype?
Phenotype = Phenylketonuria

45. Phenylketonuria (PKU)
What percentage of the U.S. population
who do not have PKU are carriers (Rr) ?

46. Phenylketonuria (PKU)
So if one out of 10,000 babies are born with PKU, what is the frequency of rr ?
frequency of rr = q2
q2 =
What is q ?
q = square root of or 0.01

47. Phenylketonuria (PKU)
What is p ?
(or the frequency of the dominant allele?)
p = 1 minus q
p = 0.99

48. What percentage of the U.S. population
who do not have PKU are carriers (Rr) ?
= 2pq
= 2 X X 0.01
= or 1.98% or about 2%

49. Main causes of evolution (mechanisms that change a gene pool)
1) Natural Selection
2) Genetic Drift
Bottleneck Effect
Founder Effect
3) Gene Flow

50. Genetic Drift = a change in the gene pool of a population due to chance, usually occurring in a small population
A common result of genetic drift is the loss of all but one possible allele in a population, called genetic fixation

51. Genetic Drift
There are two main ways a population would shrink down to a small size
1) Bottleneck Effect
2) Founder Effect

52. Bottleneck Effect
Disasters such as earthquakes, floods or fires may kill large numbers of organisms, producing a small surviving population.

53. Bottleneck Effect
Number of cheetahs fell drastically during last ice age (about 10,000 years ago) and a second time during the 1800s, when framers hunted the cheetah to near extinction.

54. Founder Effect
Founder effect is the establishment of a small, new population whose gene pool differs from that of the parent population
For example a few individuals may colonize an isolated island, lake, or other new habitat

55. Founder Effect
In 1814, a group of 15 people founded a British colony on Tristan da Cunha, a cluster of small islands in the middle of the Atlantic Ocean.
One colonist carried a recessive allele for retinitis pigmentosa, a form of blindness.
Recently the frequency of this allele was ten times higher on Tristan da Cunha than in the British population from which the founders came.

56. Gene Flow
Gene flow is when a population gains or loses alleles when fertile individuals move into or out of the population or when gametes (such as plant pollen) are transferred between populations

57. Gene Flow
Gene flow tends to reduce differences between populations.