MIT6_047f08_lec11_slide11

MIT6_047f08_lec11_slide11 - MIT OpenCourseWare...

Info iconThis preview shows pages 1–15. Sign up to view the full content.

View Full Document Right Arrow Icon
MIT OpenCourseWare http://ocw.mit.edu 6.047 / 6.878 Computational Biology: Genomes, Networks, Evolution Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Computational Biology 6.047 10/09/08 Guest Lecture: Molecular evolution: traditional tests of neutrality Dr. Daniel Neafsey Research Scientist, Broad Institute
Background image of page 2
Mutation+Selection=Evolution Relative importance of each for maintaining variation in population?
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Early Criticism of Darwin Blending inheritance, ‘gemmules’ Fleeming Jenkin (1867): Var [ X ( t +1)] = ½ Var [ X ( t )] X =
Background image of page 4
Mendelian Inheritance published 1865-66, rediscovered 1900 Law of Segregation: • allelic variation • offspring receive 1 allele from each parent • dominance/recessivity • parental alleles ‘segregate’ to form gametes Law of Independent Assortment
Background image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Simple case: no selection The Hardy-Weinberg Law (1908) Requires: • infinite population size • random mating • non-overlapping generations • no selection, mutation, or migration
Background image of page 6
The Hardy-Weinberg Law Genotype: AA Aa aa Frequency at time 0: u 0 v 0 w 0 u 0 + v 0 + w 0 = 1 frequency of A ( p 0 ) = u 0 + v 0 /2 frequency of a ( q 0 ) = w 0 + v 0 /2 p 0 + q 0 = 1
Background image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
The Hardy-Weinberg Law Genotype: AA Aa aa Frequency at time 0: u 0 v 0 w 0 Mating Pair Frequency Offspring AA Aa aa AA x AA u 0 2 100 AA x Aa u 0 v 0 ½½0 Aa x AA u 0 v 0 Aa x Aa v 0 2 ¼½¼ Frequency of AA in next generation: u 1 = u 0 2 + u 0 v 0 + 1/4 v 0 2 = ( u 0 + v 0 /2) 2 = p 0 2
Background image of page 8
The Hardy-Weinberg Law If assumptions met: •allele frequencies don’t change •after a single generation of random mating, genotype frequencies are: u = p 2 v = 2 pq w = q 2 •entire system characterized by one parameter ( p ) Deviation from expectations indicates failure of 1 or more assumptions—selection?
Background image of page 9

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
HW application: Sickle cell anemia =SS =ss Observed Expected Counts Counts SS 834 Ss 161 ss 5 2 pq *1000= 129 p = 0.834 = 0.91 q = 0.005 = 0.071
Background image of page 10
Approach: Detect selection through comparison to neutral expectation Kimura: neutral theory Ewens: sampling formula Coalescence
Background image of page 11

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Neutral Theory History • Motoo Kimura (1924-1994) • 1968: a large proportion of genetic change is not driven by selection • Adapted diffusion approximations to genetics • Dealt with finite pops
Background image of page 12
Genetic Drift no drift infinite pop drift finite pop
Background image of page 13

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Neutral allele diffusion t = 100 t = 40 t = 500 t = 28 t = 10 0.0 1.0 2.0 0.0 0.5 1.0
Background image of page 14
Image of page 15
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 09/24/2010 for the course EECS 6.047 / 6. taught by Professor Manoliskellis during the Fall '08 term at MIT.

Page1 / 44

MIT6_047f08_lec11_slide11 - MIT OpenCourseWare...

This preview shows document pages 1 - 15. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online