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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Powerpoint Lecture Outline Human Genetics Concepts and Applications Eighth Edition Ricki Lewis Prepared by Dubear Kroening University of Wisconsin-Fox Valley 14-1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 14 When Allele Frequencies Stay Constant 14-2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Population • Is an interbreeding group of the same species within 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 alleles can move between populations when individuals migrate and mate 14-3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Allele Frequencies Allelic Frequency # of particular allele total # of alleles in the population • Count both chromosomes of each individual • Allele frequencies affect the genotype frequencies – The frequency of each type of homozygote and heterozygote in the population 14-4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Phenotype Frequencies • Frequency of a trait varies in different populations Table 14.1 14-5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microevolution • Genetic change due to changing allelic frequencies in populations • Allelic frequencies can change when: – Nonrandom mating – Gene flow – Genetic drift – Mutation – Natural selection (unequal reproductive success) • Macroevolution – The formation of new species 14-6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Microevolution • When the relative frequencies of alleles in a population change over a number of generations, evolution is occurring on its smallest scale (microevolution) 14-7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. There are several potential causes of microevolution • Genetic drift is a change in a gene pool due to chance (smaller populations) – Genetic drift can lead to the founder Effect and cause the bottleneck effect • Gene flow can change a gene pool due to the movement of genes into or out of a population • Mutation changes alleles • Nonrandom mating • Natural selection leads to differential reproductive success 14-8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Drift • Natural selection is not the only source of evolutionary change. • The smaller a population is, the farther the results may be from what the laws of probability predict. This kind of random change in allele frequency is called genetic drift. • How does genetic drift take place? – In small populations, individuals that carry a particular allele may leave more descendants than other individuals do, just by chance. – Over time, a series of chance occurrences of this type can cause an allele to become common in a population. 14-9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Drift Sample of Original Population Descendants Founding Population A Founding Population B 14-10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equilibrium: • If a population’s gene pool remains constant, then the population will not evolve. (Hardy-Weinberg Equilibrium) 14-11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equilibrium • Developed by mathematicians • A condition in which allele frequencies remain constant • Used algebra to explain how allele frequencies predicts genotype and phenotype frequencies in equilibrium 14-12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg principle • The Hardy-Weinberg principle states that allele frequencies in a population will remain constant unless one or more factors cause those frequencies to change. • The situation in which allele frequencies remain constant is called genetic equilibrium (juh-net-ik ee-kwih-lib-ree-um). • If the allele frequencies do not change, the population will not evolve. 14-13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Five conditions are required for Hardy-Weinberg equilibrium Evolution v/s Equilibrium • Five conditions are required to maintain genetic equilibrium from generation to generation • The population is very large • The population is isolated • Mutations do not alter the gene pool • Mating is random • All individuals are equal in reproductive success 14-14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 14-15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equation: • Used to calculate the frequency of alleles p2 + 2pq + q2 = 1 • Frequency of WW + Frequency of Ww + Frequency of ww = 1 • The combined frequencies of all alleles must be 100% 14-16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equilibrium p = allele frequency of one allele q = allele frequency of a second allele p+q=1 All of the allele frequencies together equals 1 or the whole collection of alleles p2 + 2pq + q2 = 1 All of the genotype frequencies together equals 1 p2 and q2 genotype frequencies for each homozygote 2pq genotype frequency for heterozygotes 14-17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 14.3 14-18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equilibrium Generation 1 p allele frequency of D normal finger length = .7 q allele frequency of d short middle finger = .3 Genotype frequencies DD p2 = (.7)2 = .49 Gamete frequencies Dd 2pq = 2 (.7)(.3) = .42 .49 Frequency D gamete = .7 .21 dd q2 = (.3)2= .09 .21 .09 frequency d gamete = .3 14-19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equilibrium Figure 14.4 14-20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Hardy-Weinberg Equilibrium Figure 14.4 14-21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 14.2 14-22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The Hardy-Weinberg equation is useful in public health science • Public health scientists use the HardyWeinberg equation to estimate frequencies of disease-causing alleles in the human population – Example: phenylketonuria (PKU) 14-23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The evolution of antibiotic resistance in bacteria is a serious public health concern • The excessive use of antibiotics is leading to the evolution of antibioticresistant bacteria – Example: Mycobacterium tuberculosis – MRSA Figure 13.22 14-24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Adaptive change results when natural selection upsets genetic equilibrium • Natural selection results in the accumulation of traits that adapt a population to its environment – If the environment should change, natural selection would favor traits adapted to the new conditions 14-25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. VARIATION AND NATURAL SELECTION Variation is extensive in most populations • Phenotypic variation may be environmental or genetic in origin – But only genetic changes result in evolutionary adaptation 14-26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. How natural selection affects variation • Natural selection tends to reduce variability in populations – The diploid condition preserves variation by “hiding” recessive alleles – Balanced polymorphism may result from the heterozygote advantage 14-27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Applying Hardy-Weinberg Equilibrium • Used to determine carrier probability • Homozygous recessive used to determine frequency of allele in population (phenotype is genotype) 14-28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Calculating the Carrier Frequency of an Autosomal Recessive Figure 14.5 14-29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 14.3 14-30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Calculating Risk with X-linked Traits Females: p2 + 2pq + q2 = 1 Males: p+q=1 All of the women in the population All of the men in the population Hemophilia is X-linked and occurs in 1 in 10,000 males p = 1/10,000 = .0001 therefore q = .9999 Carrier females = 2pq = 2 (.0001) (.9999) = .0002 1 in 5000 are carriers Affected females = p2 = (.0001) 2 1 /100 million women = .00000001 will have hemophilia 14-31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Calculating Carrier Frequency for X-linked Traits Figure 14.6 14-32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Profiling • Hardy-Weinberg equilibrium applies to portions of the genome that do not affect phenotype • They are not subject to natural selection • Short repeated segments that are not protein encoding, distributed all over the genome • Detects differences in repeat copy number • Calculates probability that certain combinations can occur in two sources of DNA • Requires molecular techniques and population studies 14-33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Table 14.4 14-34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Comparing DNA Repeats Figure 14.7 14-35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Profiling • Developed in 1980s • Identifies individuals • Used in forensics, agriculture, paternity testing, and historical investigations • DNA can be obtained from many sources 14-36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Figure 14.8 14-37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Identification Figure 14.9 14-38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. A Sneeze Identifies Art Thief Table 14.6 14-39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Profiling Techniques • (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 14-40 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Profiling Techniques • (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 14-41 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Box Figure 14.1 14-42 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Comparing DNA Sequences Figure 14.10 Figure 14.10 14-43 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. DNA Profiles • Databases are essential for statistical analysis • Nuclear and mitochondrial DNA can be used • Very small amounts of DNA can be used • Recent examples of large scale analysis – World Trade Center victims – 2004 Asian tsunami disaster – Hurrican Katrina 14-44 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Genetic Privacy • DNA dragnets • Health care concerns • Health Insurance Portability and Accountability Act (HIPAA) 14-45