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1. Lab 1

1. Lab 1






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    1. Lab 1 1. Lab 1 Presentation Transcript

    • 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. # Hand your assignment in due time. # Do your best with the lab. reports
    • 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 3 th.
      • The questions will cover materials from the population
      • genetics lab and the classification and phylogeny lab.
    • Population Genetics
      • Evolution
      • Mechanisms of evolution
      • How to prove it
      • How to measure evolution
    • 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
    • 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
    • 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).
    • Natural selection
    • Genetic drift
    • 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.
    • Gene flow
    • 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.
    • Evolution
    • 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
    • Hardy-weinberg theory (equilibrium) A a A a sperm eggs AA Aa Aa aa Punnett square Frequency of event= actual number of occurrence total number of events
    • 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
    • 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 ( X 2 ) P.200
      • X 2 =  (O # – E# ) 2
      • E#
      •  X 2 = 0
      • it is hardy-weinberg equilibrium ( H 0 or null hypothesis)
      • The higher the value of X 2 , than that obtained by chance,
      • the more likely to be significant
    • How to measure evolution  Degree of freedom : number of categories that are free to vary indepenantly . df = total number of categories - 1
    • 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