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Population Genetics

2pq 2pq • prob a passed to male sib ½ • prob a

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Unformatted text preview: 2pq + 2pq • Prob a passed to male sib ½ • Prob a passed to sister ½ • Prob both bro+sister pass a ¼ Effect of Mating of Close Relatives on Homozygosity • Which of the following most closely approximates the risk of an affected child from a brother-sister mating in a population in which q=0.001? a) 1/1000 b) 1/4000 c) 1/10,000 d) 2p/N e) 2q/N Compared to outbred risk… if q=1/1000, then 2q x 2q x ¼ = 1/1,000,000 Relatedness and Inbreeding Challenge: Two full brothers marry two full sisters. Each of these two couples produce a biological child and these “cousins” later wish to marry. Calculate the value of R for these “cousins” and the value of F for the future children of these “cousins”. Random Events • Random Genetic Drift and the Founder Effect • through random changes in allele frequency, populations eventually drift to p=1 or p=0 • Allele frequencies can change dramatically in single generation, especially in small populations with small # offspring (basically a sampling “error”) • Thus two isolated populations could, via random genetic drift, diverge toward fixation of either the A or the a allele Bottlenecks and Population Size Founder Effect, Recovery or Extinction Risk of Extinction Greater for Small Populations • 3 main reasons: – loss of genetic variability and related problems of inbreeding and genetic drift – demographic fluctuations due to random variations in birth and death rate – environmental fluctuations due to variation in predation, competition, disease and food supply; and natural catastrophes that occur at irregular intervals, such as fires, floods, volcanic eruptions, storms and droughts Random Events • Founder effect (“acute drift”)- small population size – rare allele becomes very common if introduced into small population, either due to chance (stochastic) or proliferative parent • lack of B blood group in Native Americans, whose ancestors migrated across Bering Strait 20,000 years ago • Genetic “bottlenecks” in zoo populations, island dwellers, ethnic/religious cloisters Genetic Drift and Population Size simulations, N = 10 and 100 20 alleles, 50 generations The War on Baby Girls Gendercide,Mar 4th 2010 From The Economist print edition Excess of Males Gendercide, Mar 4th 2010 From The Economist print edition Male:Female Ratios Gendercide, Mar 4th 2010 Effects of Disturbed Sex Ratio • Increased crime – Status depends on marriage/children – Crime has doubled in China in past 20 yrs • Violence against women – bride abduction, prostitution, sex trafficking, rape • Increased savings – bride price increasing • Increase in suicide rates in women S. Korea reversing its preference for sons Race/ethnicity in medical genetics • Genetic disease prevalence – Genetic screening (Tay Sachs, CF, Sickle cell) • Allele frequency estimates • SNP profiling – drug sensitivity Ethnic differences in the distribution of SNPs in 36 cardiovascular disease-associated genes...
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2pq 2pq • Prob a passed to male sib ½ • Prob a passed...

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