Genes within Populations

1. Genes within Populations

2. What is a population? How are populations characterized? What does it mean to be diploid, haploid, polyploid? How can we characterize populations based on their genes?

3. What is a population? • A group of individuals of the same species that have a high potential of interbreeding • Share a common gene pool

4. Phenotype & Genotype • The phenotype is the expression of the genetic material (the genes) of the chromosomes. • The genotype relates to the alleles found at loci on the chromosomes

5. How many alleles can an individual have at a locus? How many alleles can there be in a population at a specific locus?

6. Determining the genotype for an enzyme in a fish.

7. IDHP (isocitrate dehydrogenase) from a grasshopper Individuals 2 1 3 . . . AA Aa aa

8. Genotype There are 3 Genotypes AA and aa (Homozygous), and Aa (Heterozygous)there are 2 alleles A and a

9. Genotype frequency • If there are 100 individuals60 are AA • 30 are Aa • 10 are aa Genotype frequency AA= 60/100= 0.6 Aa = 30/100= 0.3 aa= 10/100 = 0.1Total = 1.0

10. Allele Frequency • in 100 individuals there are 200 alleles 60 indiv. AA = 120 A 30 indiv. Aa = 30 A and 30 a 10 indiv. aa = 20 a Therefore A = 150 A=150/200 = 0.75 a = 50 a=50/200 = 0.25

11. Phenotype • there are 2 phenotypestrait “X” (AA and Aa) and trait “Y” (aa)

12. Phenotype frequency • trait X = 90 indiv. (AA and Aa)trait Y = 10 indiv. (aa)Freq. X = 90/100 = 0.9Freq. Y =10/100 = 0.1

13. Hardy-Wienberg Equilibrium • If p = proportion of allele A and if q = proportion of allele a • Then p+q = 1 • Hardy-Wienberg Equilibrium gives the expected frequency of the three genotypes as: (p+q)2 = p2 +2pq + q2 = 1 AA = p2, aa = q2 and Aa = 2pq

14. Hardy-Wienberg EquilibriumAssumptions • Population size is very large • Random mating is occurring • No mutation is taking place • No immigration (geneflow)‏ • No selection is occurring

15. If the proportion of genotype aa in a population = 1% or 0.01 • aa = 0.01 • q2 = aa • Therefore q = square root of 0.01 =0.1 • p= 1 - 0.1 = 0.9 • AA = p2 = 0.81 • Aa = 2pq =0.18 • aa = q2 = 0.010

17. How the Hardy-Wienberg Equilibrium can be used!

18. Extension to Hardy-Wienberg • Three alleles

20. Genotype frequency p12 + 2p1p2 + 2p1p3 + p22 + 2p2p3 + p32 = 1

21. 3 alleles therefore 6 genotypes • genotype q2 =.01, z2 = 0.04 genotypes = q2+z2+p2+2qz+2zp+2pq alleles p+q+z=1 Genotypes are: q= 0.1, z= 0.2, p= 0.7 p2= 0.49 q2=0.01 z2=0.04 2pz=0.28 2pq=0.14 2zq=0.04

22. Populations share a common gene pool!What does this mean? • At each gene locus a population will be characterized by a particular allele frequency. The combination of allele frequencies is what characterizes a population and potentially makes populations unique.

23. What will cause deviation from Hardy-Wienberg Equilibrium?

24. Genetic Drift • For small populations random chance may result in the loss of an allele! • Results in Fixation • Loss of heterozygosity

25. Genetic drift is a random process

26. What is inbreeding and why is it bad?

27. Inbreeding alleles are common by descent

28. Genes common by descent • Loss of heterozygosity • No loss of alleles

29. Other Processes GENE FLOW – result of dispersal (an individual leaving one population and entering another population). Gene flowcounters genetic drift. FOUNDER EFFECT – refers to the chance genecombination in newly founded population (the variation in a new pop. Generally less thanvariation in the source population). GENETIC BOTTLENECK – when a population is reduced tonumbers but then recovers some genetic variation isgenerally lost.

31. What generalities and patterns are there? Selection is a change in allele frequency which is directional, NOT random.