University:
Boston University
Course:
CAS BI 108 | Biology 2
Academic year:

2024
Views:

230

Pages:

18
Author:

Melina Hobbs

Exploring the complicated role of evolutionary modeling in paleobiology Overview • Two instances where evolutionary modeling meets human paleobiology 1. Sequence evolution models behind molecular tests for natural selection 2. Models of cooperation in connection with the evolution of human cognition and social behavior • Conclusion: comparison and a coincidence 1. Signatures of selection 1. Signatures of selection • Evolution by natural selection occurs when there is variation in some trait, that variation is responsible for differences in evolutionary fitness, and the trait is heritable 1. Signatures of selection • Evolution by natural selection occurs when there is variation in some trait, that variation is responsible for differences in evolutionary fitness, and the trait is heritable • A signature of selection is a detectable trace that coheres with a specific selection hypothesis 1. Signatures of selection • Evolution by natural selection occurs when there is variation in some trait, that variation is responsible for differences in evolutionary fitness, and the trait is heritable • A signature of selection is a detectable trace that coheres with a specific selection hypothesis • The epistemic risk: such signatures may be artifactual—they may cohere with some selection hypothesis but be produced by different causes Molecular signatures Molecular signatures • Molecular detection methods use sequence data (primarily DNA) Molecular signatures • Molecular detection methods use sequence data (primarily DNA) ‣ Ratio of nonsyn. to syn. substitution rates (dn/ds) Molecular signatures • Molecular detection methods use sequence data (primarily DNA) ‣ Ratio of nonsyn. to syn. substitution rates (dn/ds) ‣ MK tests - within vs. between species variation Molecular signatures • Molecular detection methods use sequence data (primarily DNA) ‣ Ratio of nonsyn. to syn. substitution rates (dn/ds) ‣ MK tests - within vs. between species variation ‣ Hitchhiking effects - selective sweeps Molecular signatures • Molecular detection methods use sequence data (primarily DNA) ‣ Ratio of nonsyn. to syn. substitution rates (dn/ds) ‣ MK tests - within vs. between species variation ‣ Hitchhiking effects - selective sweeps ‣ Frequency spectrum Frequency spectrum Frequency spectrum • Sample DNA sequences (of the same gene) from several individuals within a species Frequency spectrum • Sample DNA sequences (of the same gene) from several individuals within a species • Compare sequences, determine the number of alleles (segregating sites), and the frequency of each allele in the sample Frequency spectrum • Sample DNA sequences (of the same gene) from several individuals within a species • Compare sequences, determine the number of alleles (segregating sites), and the frequency of each allele in the sample • Frequency spectrum: a distribution of the number of segregating sites that occur at a specific frequency in the sample data Frequency spectrum More precisely, the distribution of the number of sites x at some frequency across a sequence sample size of n. i xi : number of sites at frequency = , n for i = 1, . . . , n 1 E(xi ) 1 i and depends on , = 4Ne µ Figure 2 From Nielsen 2005 based on Sawyer & Hartl 1992 The frequency spectrum under a selective sweep, negative selection, neutrality, and positive selection.