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Population Genetics

Population Genetics. “The study of genetic variation and its causes in population”. Suggestion to do well in this class # Attend every lab session. # Give your undivided attention. # Ask the TA to repeat himself. # Review the power-point presentations before the quiz.

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Population Genetics

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  1. Population Genetics “The study of genetic variation and its causes in population”

  2. Suggestion to do well in this class # Attend every lab session. # Give your undivided attention. # Ask the TA to repeat himself. # Review the power-point presentations before the quiz. # Hand your assignment in due time. # Do your best with the lab. reports

  3. Announcements • Cedo field trip. • preceptor program • Home assignment include game 1, 2, and questions 1, 3 and 4 • on page 12 • There will be a quiz (8 points) on Thursday, February 3th. • The questions will cover materials from the population • genetics lab and the classification and phylogeny lab.

  4. Population Genetics • Evolution • Mechanisms of evolution • How to prove it • How to measure evolution

  5. Evolution • Population is a group of individuals that coexist in certain place at the same time and capable of interbreeding with one another • Evolution is change over time in the traits of a population • Phenotype is the observable properties of an organism. • Gene is piece of DNA that codes for a protein • Alleles are different forms of a gene

  6. Evolution • Genotype is the genetic composition the governs • a trait (AA, Aa, aa) • Evolution is change of the allele frequencies over time. • Dominant allele, determine the phenotype of • heterozygous individuals. • Recessive allele, shows its phenotype only in • homozygous individuals

  7. Forces of evolution • Natural selection advantage in survival and reproduction. • Mutations. random changes in nucleotide sequence. • Migration (gene flow). new individuals are introduce to the population. • Non-random mating. possession or absence of certain phenotype. • Genetic drift. random changes (allele fixation in small population).

  8. Natural selection

  9. Genetic drift

  10. Genetic drift • Its effect is clear in small populations • These populations lose genetic variability rapidly. • alleles drift to fixation. • http://darwin.eeb.uconn.edu/simulations/drift.html.

  11. Gene flow

  12. Applied aspects of population genetics Cystic fibrosis Cystic Fibrosis (CF) is the most common AR (autosomal recessive) disorder found in Caucasians with an estimated incidence of 1 in 2500 in newborns of European ancestry. About 1 in 25 persons of European ancestry is a carrier.CF especially affects the respiratory and digestive systems. The CF gene was identified in 1989. The average life expectancy of a person with CF is now at 30 years, due to advances in medical care.

  13. Evolution

  14. How to prove that evolution occur • Hardy-weinberg theory (equilibrium) A population that is not changing genetically from generation to generation.(null hypothesis) • Essential assumptions 1-Mating is random 2-Population size is very large (no effect for genetic drift) 3-Mutations can be ignored 4-Natural selection has no effect 5-No migration

  15. Hardy-weinberg theory (equilibrium) sperm A a AA Aa A Punnett square eggs aa Aa a Frequency of event= actual number of occurrence total number of events

  16. Hardy-weinberg theory (equilibrium) • Allele frequency = number of occurrence of that allele total number of alleles in the population • Genotype frequency= number of occurrence of that genotype total number of the population or product of its alleles frequency= p * q Note: frequency is just another way to express (absolute)numbers. It is just the decimal fraction • p + q =1 • p2 + 2pq + q2 = 1

  17. How to measure evolution • Calculate allele and genotype frequencies in each generation and compare it to the previous one. • are differences in genotype frequency from generation to generation evident? Are we sure that these differences have not happened due chance alone? • Significance of the difference in frequency chi-square analysis ( X2 ) P.200 X2 =  (O # – E# )2 E#  X2 = 0 it is hardy-weinberg equilibrium ( H0 or null hypothesis) • The higher the value of X2, than that obtained by chance, the more likely to be significant

  18. How to measure evolution  Degree of freedom : number of categories that are free to vary indepenantly . df= total number of categories - 1

  19. Questions 1a- population in game 2 1b- for game 2, we have high confidence because the probability of sampling error were less than 5% . For game 1, vice versa.. 1c- population in game 1 1d- population in game 2 because evolutionary force (natural selection) was acting in the population. 3a- by natural selection 3b-heterozygous individuals 4- aa= 0.7x 0.7=0.49 AA=0.3x0.3=0.09 Aa=0.3x0.7=0.21 = 0.21x2=0.42

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