2 Population = An interbreeding group of the same species in a given geographical area Gene pool = The collection of all alleles in the members of the population Population genetics = The study of the genetics of a population and how the alleles vary with time Gene Flow = Movement of alleles between populations when people migrate and mate

3 Hardy-Weinberg Equation Developed independently by an English mathematician and a German physician Used algebra to explain how allele frequencies predict genotypic and phenotypic frequencies in a population of diploid, sexually- reproducing species Disproved the assumption that dominant traits would become more common, while recessive traits would become rarer

4 Allele Frequencies Allele frequency = # of particular allele Total # of alleles in the population Count both chromosomes of each individual Frequencies are often expressed as decimals - The frequency of the two homozygotes and the heterozygote in the population= Hardy Weinberg equation

5 Frequency of a trait varies in different populations Table 14.1 Phenotype Frequencies

6 Figure 14.3 Source of the Hardy-Weinberg Equation Figure 14.3

7 Gamete (allele) Frequencies : Freq(A) = p Freq(a) = q  p + q = 1 Genotype Frequencies of 3 Possible Zygotes : AAAaaa Freq (AA) = p A x p A = p A 2 Freq (Aa) = (p A x q a ) + (q a x p A ) = 2p A q a Freq (aa) = q a x q a = q a 2  p 2 + 2pq + q 2 = 1

8 Solving a Problem

9 The allele and genotypic frequencies do not change from one generation to the next Thus, this gene is in Hardy-Weinberg equilibrium

10 Figure 14.3 Applying the Hardy-Weinberg Equation Used to determine carrier probability For autosomal recessive diseases, the homozygous recessive class is used to determine the frequency of alleles in a population - Its phenotype indicates its genotype

11 Table 14.3 Calculating the Carrier Frequency of an Autosomal Recessive

12 Figure 14.3 Calculating the Carrier Frequency of an Autosomal Recessive Figure 14.5

13 Figure 14.3 Calculating the Carrier Frequency of an Autosomal Recessive disease ( CF) What is the probability that two unrelated Caucasians will have an affected child? Mendelian solution involves probability or punnett squares Probability that both are carriers = 1/23 x 1/23 = 1/529 Probability that their child has CF = 1/4 Therefore, probability = 1/529 x 1/4 = 1/2,116

14 Figure 14.3 Calculating the Risk with X-linked Traits For females, the standard Hardy-Weinberg equation applies p 2 + 2pq + q 2 = 1 However, in males the allele frequency is the phenotypic frequency p + q = 1

15 Calculating the Risk with X-linked Traits Figure 14.6

16 A few things to keep in mind as we take an excursion into population genetic theory: “Make things as simple as possible, but no simpler.” ---Einstein “No theory should fit all the facts because some of the facts are wrong.” ---Bohr

17

18 Mechanisms of Evolution: Mendelian Genetics in Populations  Genetic variation is the raw material of evolutionary change: how do we measure it?  What are the forces that cause genetic changes within populations? That is, what mechanisms cause evolutionary change?

19 1. Mutation = ultimate source of variation 2. Natural selection = genotypes best suited to survive and reproduce in a particular environment give rise to a disproportionate share of the offspring 3. Migration = the movement of organisms among subpopulations 4. Random genetic drift = the random, undirected changes in allele frequencies, especially in small populations Changing Allele Frequencies

20 MUTATIONSELECTION DRIFTMIGRATION POPULATIONS Phenotypic Evolution: Process + +/ — — —

21 Darwin’s Observations and Inferences Inference 1: Production of more individuals than can be supported by the environment leads to a struggle for existence among individuals, with only a fraction of offspring surviving in each generation.

22 Inference 2: Survival in the struggle for existence is not random, but depends in part on the inherited characteristics of individuals Darwin’s Observations and Inferences

23 Inference 3: The unequal ability of individuals to survive and reproduce leads to a gradual change in a population, with favorable characteristics accumulating over generations (natural selection). Darwin’s Observations and Inferences

24 DARWINIAN EVOLUTION BY NATURAL SELECTION  Many more individuals are born than survive (COMPETITION).  Individuals within species are variable (VARIATION).  Some of these variations are passed on to offspring (HERITABILITY).  Survival and reproduction are not random. There must be a correlation between fitness and phenotype.

25  Because Darwin knew nothing about mutation, he had no idea how variation was generated in populations  Because Darwin knew nothing about genetics or genes, he had no idea how variation was passed on to offspring (Mendel)  Darwin did not know about nonadaptive evolutionary forces, such as Genetic Drift

26  In 1900, Mendel’s laws of inheritance were “rediscovered”  Worked out laws of inheritance independently  Discovered Mendel’s work as they were publishing their own  Formed the beginning of the foundation of Genetics: Mendel is considered the “Father of Genetics”

27 MUTATIONISM AND THE IMPACT OF MENDEL Gregor Mendel’s research was published in 1866, but was not noticed until  NOTE: Darwin knew nothing about the mechanism of inheritance when he conceived of natural selection.  MUTATIONIST THEORIES (based on Mendel’s work):  Emphasized the importance of VARIATION  T. H. Morgan -- the founder of Drosophila genetics.

28  Mendel: dealt with particulate traits  Darwin: observed continuous traits Q: How would continuous traits get passed on?

29 Mutationists (+ Mendelianism)  They thought that evolution required only mutations and passing on of discrete traits Darwinists  They thought that evolution required only Natural Selection on continuous variation

30  At the heart was the question of whether Mendelian genetics and Mutation could be reconciled with mechanisms of Natural Selection.  A second issue was whether the broad-scale changes (macroevolution) seen by palaeontologists could be explained by changes seen in local populations (microevolution).

s ~ 1940s Also called the “Synthesis of Evolution and Genetics” The synthesis of population genetics (role of mutation, selection, genetic drift), paleontology, systematics Darwin and Mendel Reconciled

32 J. B. S. Haldane The Causes of Evolution 1932  Developed the mathematical theory of gene frequency change under selection (and many other interesting applications).

33 Sir R. A. Fisher The Genetical Theory of Natural Selection 1930  Fisher united Mendelian population genetics with the inheritance of continuous traits.

34

35 DNA Profiling Developed in the 1980s by British geneticist Sir Alec Jeffreys Also called DNA fingerprinting Identifies individuals Used in forensics, agriculture, paternity testing, and historical investigations

36 DNA Repeats Short repeated segments are distributed all over the genome The repeat numbers can be considered alleles and used to classify individuals Two types of repeats are important: - Variable number of tandem repeats (VNTRs) - Short tandem repeats (STRs)

37 DNA Repeats

38 DNA Profiling A technique that detects differences in repeat copy number Calculates the probability that certain combinations can occur in two sources of DNA by chance DNA evidence is more often valuable in excluding a suspect - Should be considered along with other types of evidence

39 1) A blood sample is collected from suspect 2) White blood cells release DNA 3) Restriction enzymes cut DNA 4) Electrophoresis aligns fragments by size 5) Pattern of DNA fragments transferred to a nylon sheet DNA Profiling Technique

40 6) Exposed to radioactive probes 7) Probes bind to DNA 8) Sheet placed against X ray film 9) Pattern of bands constitutes DNA profile 10) Identify individuals DNA Profiling Technique

41 Figure 2.3 DNA Fingerprinting Animation Please note that due to differing operating systems, some animations will not appear until the presentation is viewed in Presentation Mode (Slide Show view). You may see blank slides in the “Normal” or “Slide Sorter” views. All animations will appear after viewing in Presentation Mode and playing each animation. Most animations will require the latest version of the Flash Player, which is available at

42 DNA can be obtained from any cell with a nucleus STRs are used when DNA is scarce If DNA is extremely damaged, mitochondrial DNA (mtDNA) is often used For forensics, the FBI developed the Combined DNA Index System (CODIS) - Uses 13 STRs DNA Sources

43 The probability that any two individuals have same thirteen markers is 1 in 250 trillion CODIS- Combined DNA Index System Figure 14.10

44 The power of DNA profiling is greatly expanded by tracking repeats in different chromosomes The number of copies of a repeat are assigned probabilities based on their observed frequency in a population The product rule is then used to calculate probability of a certain repeat combination Population Statistics Is Used to Interpret DNA Profiles

45 To Solve A Crime Table 14.6 Figure 14.11

46 Recent examples of large-scale disasters - World Trade Center attack (2001) - Indian Ocean Tsunami (2004) - Hurricane Katrina (2005) Using DNA Profiling to Identify Victims

47 Challenges to DNA Profiling Figure 14.12

48 Today’s population genetics presents a powerful way to identify individuals Our genomes can vary in more ways than there are people in the world DNA profiling introduces privacy issues Genetic Privacy