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Gene Pool.

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Presentation on theme: "Gene Pool."— Presentation transcript:

1 Gene Pool

2 A change in the genetic make-up of a population over time.
What is Evolution? A change in the genetic make-up of a population over time.

3 How Does Evolution Occur?
There were two hypotheses

4 Evolution by acquired traits by Jean Baptiste de Lamarck

5 Do we acquire traits? Eating Show affection Defend yourself Act nutty
Climbing Eating Show affection Defend yourself Act nutty

6 These traits are not genetic so evolution does not occur

7 How Does Evolution Occur?
NATURAL SELECTION !!! (major mechanism of evolution) Darwin’s hypothesis (now a theory): Survival of the fittest…..how is fitness measured? By reproductive success Inheritable variations occur in individuals in a population. Due to competition for limited resources, individuals with more favorable variations or phenotypes are more likely to survive & produce more offspring, thus passing traits to future generations.

8 Darwin’s View of History
Like a Tree with multiple branches. Common trunk Tips of twigs = diversity of organisms living in the present. Forks = most recent common ancestor

9 Natural Selection Summary
A process in which individuals that have certain heritable traits survive & reproduce at a higher rate than others because of those traits. Over time, natural selection can increase the match between organisms & their environment. If an environment changes, or if individuals move to a new environment, natural selection may result in adaptation to these new conditions, sometimes giving rise to new species.

10 Natural Selection acts on phenotypic variations in populations
Environments change and act as selective mechanism on populations.

11 Phenotypic variations are not directed by the environment but occur through random changes in the DNA and through new gene combinations.

12 Some phenotypic variations significantly increase or decrease fitness of the organism and the population.

13 Explain 2 examples of Evolution in response to environmental change; 1 must be antibiotic resistance in bacteria

14 Examples of Natural Selection
Antibiotic resistance in bacteria Develops in several steps: Person is sick from a bacterial infection Takes antibiotics Gets better One bacteria is not killed by the antibiotics, due to genetic modification & reproduces Person gets sick again & goes to the doctor again Same antibiotic is prescribed but there’s no effect Doctor prescribes a different antibiotic which hopefully works. If bacterium continues to change it could become resistant to more antibiotics

15 Examples of Natural Selection
Pesticide resistance in rats Apply pesticide…most rats killed Due to natural variations, a few rats are not affected by the poison. They reproduce passing on the trait to some if not all of their offspring Seeing the rats, you apply the pesticide again with worse results. A new pesticide must be used.

16 Artificial Selection Darwin used these examples to help him derive another piece of his theory. Humans impact the gene variation.

17 What Evidence is there that Evolution by Natural Selection occurs?
Direct observations Peppered moths Drug resistant bacteria Analysis of similarities among different organisms. Homologous structures Vestigial structures Fossil Record Documents the pattern of evolution Shed light on origin of new groups of organisms Biogeography Geographical distribution of species Continental drift (slow movement of the continents over time) Help make predictions of where fossils of groups of organisms can be found

18 Direct observations

19 Analysis of similarities among different organisms
Homologous structures: represent variations on a structural theme that was present in their common ancestor. Vestigial structures: remnants of features that served important functions in the organism’s ancestors.

20 Convergent Evolution: independent evolution of similar features in different lineages.
Species that share features because of convergent evolution are said to be analogous. Analogous features share similar function but not common ancestry.

21 Fossil Record Fossils can be dated, this helps us provide evidence of evolution by dating rocks where fossils are found, it helps indicate the relationships within phylogenetic trees, as well as chemical properties &/or geographical data. Allow us to take a look at how new groups came about & when characteristics showed up. EX: Cetaceans are closely related to even-toed ungulates.

22 Biogeography We can use our understanding of evolution and continental drift to predict where fossils of different groups of organisms might be found. EX: Horses Fossil dating indicates horses originated in North America 5 million years ago. Since North & South America were not yet connected it was predicted that the oldest horse fossils would be located in North America. So far the prediction has been upheld

23 The environment does not direct the changes in DNA, but acts upon phenotypes that occur through random changes in DNA These changes can involve alterations in DNA sequences, changes in gene combinations, and/or the formation of new gene combinations.

24 Environments are always changing
No “perfect” genome (entirety of an organism's hereditary information). Diverse gene pool = long term survival in a changing environment. Mutations contribute to diversity Some are silent Some result in phenotypic difference Interaction of the environment & phenotype determines fitness.

25 What does “survival of the fittest” mean?
The species that are most adapted in their environment by reproducing more successfully will survive.

26 Mutation Change in the nucleotide sequence (are rare; change from gen. to gen. is very small. In multicellular organisms, only mutations occurring in gametes will be passed on to offspring Most occur in somatic cells. Some are “silent” changes Point mutation

27 Genes duplicating Due to errors in meiosis During DNA replication
Activities of transposable elements (wandering DNA segments) Large chromosome segment duplications are usually harmful Smaller pieces of DNA may not be. Gene duplications that don’t have severe effects can persist & accumulate = potential new genes with new functions.

28 Example of Beneficial Increases in Gene Numbers
A remote ancestor had a single gene for detecting odors & have duplicated over time. Today we have about 1,000 olfactory receptor genes.

29 Evolving Populations What is a population?
A group of individuals of the same species that live in the same area & interbreed, producing fertile offspring.

30 We can characterize a population’s genetic make-up by describing its gene pool.
What is a gene pool? The total number of genes of every individual in an interbreeding population. The size of the gene pool affects the rate of mutation

31 Why is it vital to have diversity in the gene pool?
Environmental conditions change What kills one would kill them all.

32 Clearing Potential Misunderstandings
Natural selection acts on ___________ Ex: pepper moths _____________not individuals evolve. Organisms that are _______________ fit will pass on their _________. PHENOTYPE POPULATIONS REPRODUCTIVELY GENES

33 G.H. Hardy & W. Weinberg (1908) Both men independently suggested a scheme whereby evolution could be viewed as changes in the frequency of alleles in a population of organisms.

34 Calculating changes in allele frequency
Hardy-Weinberg For populations to be at equilibrium (remain constant) the following conditions must be met. Population must be large Absence of migration No net mutations Random mating Absence of selection These conditions are seldom if ever met.

35 Of what value is this? Provides a yardstick by which changes in allele frequency, & therefore evolution, can be measured.

36 The Hardy-Weinberg Equation
Tests whether a population is evolving.

37 The Hardy-Weinberg Principle
The equation determines what the genetic make-up of a population would be if it were not evolving at that locus. Those results are compared to data from an actual population If there are no differences, it can be concluded that the “real” population is not evolving It is also used in medical applications: Est. the % of a population that carries the allele for an inherited disease.

38 Knowing the frequency of the phenotype, you can calculate the frequency of the genotypes and alleles in the population. Because there are only two alleles, the sum of p and q must always equal 1. This equation finds the allele frequency p + q = 1 = frequency of the dominant allele =frequency of the recessive allele

39 The Hardy-Weinberg equilibrium can be written as an equation
p2 q2 1 2pq + = + % of Individuals homozygous for allele bb written as a decimal % of Individuals homozygous for allele BB written as a decimal % of Individuals heterozygous for alleles Bb written as a decimal By convention The more common allele (B) is designated p The less common allele (b) is designated q This equation lets us calculate genotypic/phenotypic frequencies in a very simple way.

40 142/546 = .26 which represents q2 or gg
Let’s say we have a population of 546 frogs. 142 of these frogs have dark spots on them. The plain green frogs are completely dominant to the spotted frogs. Determine the genotypic frequencies within this population. 142/546 = .26 which represents q2 or gg In order to get the homozygous dominant & heterozygous we need to use the p + q = 1 equation. q2 = .26  take the square root of each side to get q which is .51 p2 = .24 p + q = 1 p= 1- q p=  p = .49  2pq = 2(.51 x .49) = .50 So, 26% of the frogs are recessive; 50% are heterozygous; 24% are homozygous dominant.

41 Which means 51% of the population carries at least one g allele.
To determine the frequency of gametes carrying the dominant allele. Meaning the percent of the population carrying at least one dominant allele: You would take half of the 2pq frequency and add it to the p2 frequency. = .49 Which means, 49% of the frog population carry at least one dominant allele. To determine the recessive frequency take half of the 2pq & add to q2 = .51 Which means 51% of the population carries at least one g allele.

42 Cystic fibrosis is caused by the recessive allele b.
CALCULATING THE FREQUENCY OF CYSTIC FIBROSIS Cystic fibrosis is caused by the recessive allele b. Calculate the frequency of the recessive allele If q2, the frequency of recessive homozygotes, is , then q is , or Calculate the frequency for the dominant allele B: p + q = 1 , p = 1-q SO p = 1 – 0.022, OR Determine the frequency of heterozygotes 2pq = x x = Meaning: 43 of every 1,000 Caucasian North Americans are predicted to carry the cystic fibrosis allele unexpressed.

43 TONGUE CURLING!!! How would we determine q2? How do you determine q?
What percentage of the class are carriers for the tongue curling trait? (Tongue curling is a dominant trait.) Try to curl your tongue upwards. How would we determine q2? Divide the total number of non-curler students by the total number of students. How do you determine q? Calculate the square root of q2. Since p + q= 1; determine p. Now plug in numbers for 2pq.

44 Time for a simulation!!! Let’s Get It On!!!!

45 Genotypes # of Students # of A’s # of a’s AA Aa aa Total Genotypes # of Students # of A’s # of a’s AA Aa aa Total Genotypes # of Students # of A’s # of a’s AA Aa aa Total

46 Case Studies p= q= Genotype Frequency: TOTAL number of A alleles
TOTAL number of alleles in the population TOTAL number of a alleles q= TOTAL number of alleles in the population

47 Number of alleles present after several generations
Number of offspring with AA _____X 2= _________ A alleles Number of offspring with Aa _____X 1= __________A alleles Total= __________A alleles TOTAL number of A alleles p = TOTAL number of alleles in the population (number of students X 2)

48 Altering Allele Frequencies in Populations Directly & cause most Evolutionary Change
Natural Selection Genetic drift Gene Flow

49 Genetic Drift Random fluctuation of alleles due to chance events
More likely to occur in smaller population Founder effect Small group of individuals establishes a population in a new location Bottleneck effect A sudden decrease in population size to natural forces

50 Case Study: Genetic Drift
The land was being converted to farmland and other uses. Led to significant loss of genetic variation & an increase in the frequency of harmful alleles. A reduction of genetic variation within a given population can increase the differences between populations of the same species.

51 Gene Flow The transfer of alleles into or out of a population due to the movement of fertile individuals or their gametes. If there is gene flow between two populations there is a tendency for the amount of genetic variation between the populations to decrease.

52 Natural Selection is the only mechanism that consistently causes adaptive evolution

53 Increase in the frequency of the intermediate phenotype
Stabilizing Selection Increase in the frequency of the intermediate phenotype Fig In humans, infants with intermediate weight at birth have the highest survival rate In chicken, eggs of intermediate weight have the highest hatching success

54 Disruptive Selection In the African seed-cracker finch, large- and small-beaked birds predominate Can open tough shells of large seeds Intermediate-beaked birds are at a disadvantage Unable to open large seeds Too clumsy to open small seeds More adept at handling small seeds

55 Directional Selection
Drosophila flies that flew toward light were eliminated from the population The remaining flies were mated and the experiment repeated for 20 generations Common when environment changes or members of a population migrate out. Phototropic flies are far less frequent in the population

56 Sexual Selection Sexual selection acts on an organism's ability to obtain (often by any means necessary!) or successfully copulate with a mate. Sexual dimorphism- a difference in the 2 sexes Sexual selection is often powerful enough to produce features that are harmful to the individual’s survival. Australian Peacock Spiders

57 Operations of Sexual Selection
Intrasexual selection: Intersexual selection: Individuals of one sex compete for mates of the opposite sex. Mostly males compete but there are some species where females compete (ring-tailed lemurs and broad-nosed pipefish) “mate choice” – individuals of one sex (usually females) are choosy in selecting their mates of opposite sex. Many cases it falls to the male’s showiness or behavior that wins the female.

58 Why natural selection cannot fashion perfect organisms
Limited by species ancestors Birds ancestors are reptiles & only had 4 legs. Wings were opted for flight so that left only 2 legs left. Adaptations are often compromises Seals spend a lot of time on rocks so legs would be a better trait than flippers but then they would not swim as well. Chance & natural selection interact Snakes are carried to different islands on seaweed rafts but the snakes that are carried are not necessarily the snakes best suited to the environment. Selection can edit out only existing variations New alleles do not arise on demand

59 The biological species concept
Emphasizes reproductive isolation

60 Belonging to the same biological species
Means you are reproductively compatible, potentially. But, it all hinges on… Reproductive barriers: Impede members of two species from producing viable, hybrids. One barrier may not impede but a combination of several can isolate a species gene pool.

61 Prezygotic & Postzygotic Barriers
Impede mating or hinder the fertilization. POSTZYGOTIC: If the sperm is able to overcome the prezygotic barriers then the zygote may be prevented from developing.

62 Two main ways by which new species form

63 Speciation can take place with or without geographic separation
Reproductive barrier must be present. -allopolyploidy -reproductive isolation -habitat, food source, or other source not used by parent pop. -temporal or behavioral isolation Geographic isolation -reproductive isolation may occur; preventing interbreeding

64 Example of sympatric speciation

65 Adaptive Radiation

66 Tempo of Speciation

67

68 The study of the evolutionary past of a species.
Phylogeny The study of the evolutionary past of a species.

69 Systematics An approach to looking at the diversity & relationships between organisms living & extinct. Morphology Biochemical resemblances Molecular comparisons (ex: DNA) If similar with any they are likely to be closely related It’s also good to look at fossils- they reveal ancestral characteristics that may have been lost over time.

70 Sorting Analogy from Homology
How can you tell if the structure is similar because of a common ancestor or due to convergent evolution? Search for corroborating similarities between the species Fossil evidence Look at the complexity of the characters & note points of similarities.

71 Molecular comparisons of Nucleic Acids
Species 1 & 2 DNA are identical Begin to diverge Mutations shift the matching sequences Homologous regions (in yellow) no longer align Using a computer program homologous regions now align because appropriate gaps were created.

72 Connecting Classification with Evolutionary History

73 Binomial nomenclature
Two part naming system genus and specific epithet Canis lupus or

74 1. Cyanocitta cristata 2. Iris cristata 3. Cyanocitta stelleri
WHICH OF THE FOLLOWING ORGANISMS ARE MORE CLOSELY RELATED & EXPLAIN WHY. 1. Cyanocitta cristata 2. Iris cristata 3. Cyanocitta stelleri

75 Iris cristata Cyanocitta cristata Cyanocitta stelleri

76 Hierarchy of Classification

77 Fig. 14.3

78

79

80 Using & making a dichotomous key

81 Key: 1. Has light blue colored body… go to 2 Has dark blue colored body… go to 4 2. Has 4 legs… go to 3 Has 8 legs… Deerus octagis 3. Has a tail… Deerus pestis Does not have a tail… Deerus magnus 4. Has a pointy hump… Deerus humpis Does not have a pointy hump… go to 5 5. Has ears… Deerus darkus Does not have ears… Deerus deafus

82 Don’t worry, this won’t hurt
Now it’s your turn  Don’t worry, this won’t hurt

83 ANIMALS 4 legs 2 legs or less Has fur Has no fur Has 4 wings Has 2 wings Has no yellow coloring Has yellow coloring a) has 4 legs……………………3 b) has 2 or less legs…………..2 a) has 4 wings……………Dragi purplus b) has 2 wings……….….Flamo pinketti a) has fur……………………….4 b) no fur………………..Frogata hoppus a) no yellow coloring……...Ella phantus b) yellow coloring……………..5 a) long neck………………..Girafit neket b) no long neck………....Lionus mainto Has a long neck Does not have a long neck

84 Phylogenetic trees & cladograms are graphical representations (models) of evolutionary history that can be tested

85 Phylogenetic Tree Each branch point represents the divergence of two species from a common ancestor

86 Cladogram – depicts patterns of shared characteristics
Does not imply evolutionary history. If characteristics are homologous the cladogram can serve as a basis for a part of the phylogenetic tree. Outgroup? Ingroup?

87 Making cladograms Organism Multicellular Vertebral column Hair
Placenta Total of yeses Sponge Yes No 1 Sailfish 2 Wombat 3 Elephant 4 elephant sponge sailfish wombat placenta hair Vertebral column multicellular

88 Constructing a cladogram
Using the following animals, list as many characteristics which each organism possesses . Create & fill in a chart with the animals & the characteristics you have come up with. Build your cladogram Rhesus monkey Snapping Turtle Kangaroo Human Bull frog Tuna

89 Rhesus Monkey Human Snapping Turtle Kangaroo Bull Frog Short canine teeth Tuna Placenta Mammary glands Amniotic sac Paired legs

90 Using Amino Acid Sequences To Determine Evolutionary Relationships
Homework answers

91 Number of Differences in the Amino Acids Sequences

92 One possible answer

93 Questions from the Worksheet
Species X and Y have 25 amino acid differences. Species X and B have 10 amino acid differences in the same protein. Species Y and B have 27 amino acid differences. a) Which organism (X, Y, or B) diverged from the common ancestor first? ____________ Explain your reasoning. Y Species Y has the most differences between the other 2 species. With species X it has 25 differences and with species B it has 27 differences. This indicates that it split off from the common ancestor very early.

94 Species X and Y have 25 amino acid differences
Species X and Y have 25 amino acid differences. Species X and B have 10 amino acid differences in the same protein. Species Y and B have 27 amino acid differences. b) Which pair of organisms--X & Y, X & B, or Y & B--are likely to share more characteristics than the other two pairs. ______________ Again, explain your reasoning. X & B X and B have the fewest amino acid sequence differences between the 3 species. Having the fewest differences indicates a closer relationship.

95 Structural evidence supports the relatedness to all eukaryotes
Cytoskeleton Membrane-bound organelles Linear chromosomes Endomembrane systems, including nuclear envelope.

96 Sometimes the most obvious evidence isn’t the best
Which of these is most likely in your opinion? Sometimes the most obvious evidence isn’t the best

97 Molecular & genetic evidence from existing and extinct organisms indicates all organisms on Earth share a common ancestral origin of life Molecular building blocks are common to all life forms Common genetic code are shared by all modern organisms. Metabolic pathways are conserved across all currently recognized domains (bacteria, archea, & eukarya)

98 The Universal Tree of Life
1. Last common ancestor of all living things. 2. Possible fusion of bacterium with archea making eukaryotes 3. Symbiosis of mitochondrial ancestor with ancestor of eukaryotes 4. Symbiosis of chloroplast ancestor with ancestor of green plants

99 The History of Life on Earth
Earth formed approximately 4.6 billion years ago. The earliest fossil is dated 3.5 billion years old.

100 Primitive Earth Provided inorganic precursors from which organic molecules could have been synthesized due to the presence of available free energy & the absence of a significant quantity of oxygen. These molecules served as monomers of building blocks for the formation of more complex molecules, including amino acids & nucleotides. Joining of the monomers produced polymers with the ability to replicate, store & transfer information. The RNA World hypothesis proposes that RNA could have been the earliest genetic material.

101 Miller/Urey Experiment
This experiment showed it was possible to form complex organic molecules from inorganic molecules in the absence of life.

102 How are rocks & fossils dated?
Radiometric dating

103 Fossils have been found linking all the major groups
Fig Whale “missing links” Fossils have been found linking all the major groups The forms linking mammals to reptiles are particularly well known

104 Radiometric Dating Certain atoms are known to decay (break down) at a specific rate. Scientists can look at these atoms to determine how old an organic object is. Radioactive isotope 14C- gradually decays over time back to 14N (known as Carbon Dating) It takes ~5600 years for half of the 14C present in a sample to be converted to 14N. This length of time is called the half-life. Half life (t1/2): the time needed for half of the atoms of the isotope to decay For fossils older than 50,000 yrs scientists use other isotopes such as, potassium isotope t1/2 of 40K = 1.3 billion years to turn to argon (40Ar)

105 Mass Extinctions Are rapid during times of ecological stress.
Fossil records chronicles mass extinctions

106 1st single-celled organism
Prokaryotes 1st Eukaryotes About 2.1 billion years old. The endosymbiosis theory


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