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Population Genetics

Population Genetics. Chapter 16. 8. What is Population Genetics?. The study of genetics within populations --- not just individuals , families , and crosses Population Genetics uses Mendel’s Laws Gene and Protein Analysis Mathematical Models To understand evolution!. Basic Terms.

thomas-rodriguez
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Population Genetics

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  1. Population Genetics Chapter 16 8

  2. What is Population Genetics? The study of genetics within populations --- not justindividuals, families, andcrosses Population Genetics uses • Mendel’s Laws • Gene and Protein Analysis • Mathematical Models To understand evolution!

  3. Basic Terms Population • All members of one species in an area • Group of interbreeding individuals living in the same area Evolution Changing of a population over time • Microevolution: Change within species • Macroevolution: Creation of new species Change can include appearance, numbers, or genetic composition of a population.

  4. Gene Pool:All the genes of one trait for that population e.g. the genotypes of 20 individuals rr Rr Rr rr rr RR rr Rr Rr Rr rr rr Rr RR Rr RR rr RR Rr rr 3 If there is more than one allele, the population is Polymorphic.

  5. RR RR RR RR Rr rr rr rr rr rr rr rr rr Allele Frequency is: R = ? / 40 = ? % r = ? / 40 = ? % Rr Rr Express allele frequencies as decimals - sometimes as percentages. Rr Rr Rr Rr Rr Do the math! And the answer is... Frequency of R allele = 0.4 or 40 % Frequency of r allele = 0.6 or 60 %

  6. pp PP 2 P x In a stable population (no evolution), the allele frequencies remain the same. 1 F1 x Pp Pp F2 PP Pp Pp pp Remember the purple and white flowered peas…

  7. Hardy-Weinberg Principle Assumes a large population which is at equilibrium with its environment: 1. Diploid organisms 2. Non-overlapping generations 3. Large population 4. Nomutations 5. Sexual reproduction 6. Randommating (allele frequency is same for males & females) 7. No gene flow due to migration of individuals with a different allele frequency (immigration = in to; emigration = out of) 8. No artificial or natural selection Remember - Equilibrium means no net change!

  8. _________-____________ Principle ALLELES: p + q = 1 p = % dominant allele R q = % recessive allele r INDIVIDUALS: p2 + 2pq + q2 = 1 p2= % homozygous dominant genotype RR 2pq = % heterozygous genotype Rr q2= % homozygous recessive genotype rr If allele frequencies change, one or more H-W assumptions aren’t true.

  9. p = 0.8 (R) Allele Frequencies q = 0.2 (r) R R RR p2 = 0.64 Eggs Sperm p= 0.8 p= 0.8 r r q= 0.2 rR qp= 0.16 q= 0.2 Rr pq= 0.16 rr q2 = 0.04 p2= 0.64 (RR) 2pq = 0.32 (Rr) q2= 0.04 (rr) Genotype frequencies Figure 13.18

  10. Suppose… Frequency of R allele = 40 % or 0.4 Frequency of r allele = 60 % or 0.6 If there is environmental pressure favoring one allele over the other (natural or artificial selection), allele frequencies in the gene pool change ...this is EVOLUTION!

  11. 16.4 Microevolution in Large Populations Populations that are not in H-W Equilibrium … Natural Selection at work! Pepper Moths of England4 If there is environmental pressure favoring one allele over the other allele frequencies in the gene pool change ...this is microEVOLUTION!

  12. 5 3 Sickle Cell Anemia Caused by a 1 nucleotide substitution which changes 1 amino acid in Hemoglobin • Simple Recessive • Homozygous recessives are sick • Heterozygotes are resistant to malaria Two different forces at work here! ~ 5 min

  13. Mechanisms Affecting Gene Pools Look! All of them violate one of the H-W assumptions!

  14. Genetic Drift: Bottleneck/Founder Effect5 Population numbers decrease dramatically--- Founder effect is when a few individuals start a new population… same basic idea.

  15. Inbreeding Depression5 Over time, genetic variation (and % heterozygotes) decreases. Fertility and survival also decrease.

  16. Population 1 250 AA 150 Aa Population 2 300 Aa 100 aa Gene Flow If 50 homozygotes move from population 1 to population 2, will microevolution occur in each population? How do you know? Original frequencies: Pop 1 A = 0.81; a = 0.19. Pop 2 A = 0.38; a = 0.63. Later frequencies: Pop 1 A = 0.79; a = 0.21. Pop 2 A = 0.44; a = 0.56 .

  17. Sources Cited 1. http://www.rasayana.com.au/rasayanastory.htm 2. faculty.uca.edu/~johnc/ mendel1440.htm 3. www.sacnews.com/current.htm 4. web.nmsu.edu/~wboeckle/ biston.html 5. www.denniskunkel.com with permission 6. www.pueblo.gsa.gov/cic_text/health/ sicklecell/496_sick.html 7. BioCD. From Biology, Fifth Edition. Campbell, Reece, Mitchell. Addison, Wesley, Longman. 1999. 8. http://www.mgcpuzzles.com/mgcpuzzles/artgallery/Royce_McClure_artist/art_gallery_two.html

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