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2 Genetic structure of a population & Allele and genotype frequencies Lecture 4

3 Population genetics – Outline What is population genetics? Calculate Why is genetic variation important? - genotype frequencies - allele frequencies How does genetic structure change?

4 Why is genetic variation important? potential for change in genetic structure adaptation to environmental change - conservation Genetic variation in space and time divergence of populations - biodiversity

5 Why is genetic variation important? variation no variation north south north south

6 Why is genetic variation important? variation no variation divergence NO DIVERGENCE!! north south north south

7 The Gene Pool Members of a species can interbreed & produce fertile offspring Species have a shared gene pool Gene pool – all of the alleles of all individuals in a population

8 Populations A group of the same species living in an area No two individuals are exactly alike (variations) More Fit individuals survive & pass on their traits

9 Modern Synthesis Theory Combines Darwinian selection and Mendelian inheritance Combines Darwinian selection and Mendelian inheritance Population genetics - study of genetic variation within a population Population genetics - study of genetic variation within a population Emphasis on quantitative characters Emphasis on quantitative characters

10 Genes Within Populations

11 Allele Frequencies Define Gene Pools As there are 1000 copies of the genes for color, the allele frequencies are (in both males and females): 320 x 2 (RR) x 1 (Rr) = 800 R; 800/1000 = 0.8 (80%) R 160 x 1 (Rr) + 20 x 2 (rr) = 200 r; 200/1000 = 0.2 (20%) r 500 flowering plants 480 red flowers20 white flowers 320 RR160 Rr20 rr

12 GenotypesCounts Genotype frequencies. AA n AA D= f(AA) = n AA /n Aan Aa H= f(Aa) = n Aa /n aan aa R= f(aa) = n aa /n Total n D + H + R = 1 Allele frequencies p(A) = (2n AA + n Aa )/2n q(a) = (2n aa + n Aa )/2n Standard error of the estimate of the allele frequency Var(p A ) = p A (1 - p A )/2n Allele Frequencies Define Gene Pools

13 Calculations of allele frequencies and genotype frequencies GenotypesCountsEstimates genotype frequencies AA 224D= f( AA ) = 224/294 = Aa 64H= f( Aa ) = 64/294 = aa 6 R= f( aa ) = 6/294 = Total 294 D + H + R = =1 Allele frequencies p( A ) = (2  )/(2  294)=0.871, q( a ) = (2  6+64)/(2  294)=0.129, p( A ) + q( a ) = = 1 Expected genotype frequencies AAp 2 = = ≈ Aa 2pq = 2   = ≈ aaq 2 = = ≈ Allele Frequencies Define Gene Pools