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NORWEGIAN UNIVERSITY OF SCIENCE AND TECHNOLOGY
Faculty of Natural Sciences and Technology
Department of Biology
Subject teacher: Hans Stenøien 73596096 (91897592), Jarle Mork 90973351.
EXAMINATION IN : BI3010 Population genetics
DATE: December 5, 2005
Points: 7.5 SP
Number of pages: 2
ENGLISH
Number of hours: 4
Permitted aids: Calculator HP30S
Grades to be announced on: Dec. 27, 2005
ALL QUESTIONS COUNT AS EQUAL
___________________________________________________________________________
ANSWER EACH QUESTION (1,2,3,4,5) ON A NEW PAGE
Question 1.
A sample of N=200 specimens is taken from a natural, panmictic population of diploid organisms. At an autosomal locus with 3 alleles A, B and C, the following genotype distribution is observed.
AA: 48
AB: 62
AC: 43
BB: 15
BC: 27
CC: 5 a) Calculate: i) allele frequencies ii) observed genotype frequencies iii) Expected genotype frequencies iv) Chi-square test for Hardy-Weinberg conformity of genotype frequencies v) Observed heterozygosity vi) Expected heterozygosity b) Our null hypothesis is that the sample is taken from a population in Hardy-Weinberg equilibrium. Decide if the null hypothesis should be maintained or rejected in light of the chi-square test.
Information: The 0.05 significance level for chi-square with 1 degree of freedom = 3.84, with
2 degrees of freedom = 5.99, with 3 degrees of freedom = 7.81, with 4 degrees of freedom =
9.49.
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Question 2.
Imagine a natural population of diploid organisms and a polymorphic locus with two alleles A and B. We look at the fitness component survival. At the start of our study the genotypic distribution is: AA: 250, AB: 500, BB: 250. We assume that natural selection causes a differential genotypic mortality so that at the time of reproduction, the genotypic distribution has changed to: AA: 200, AB: 450, BB: 100.
Calculate the relative fitness coefficients and selection coefficients for the genotypes.
Give a characterization of the three main forms of selection, determine which type is operating in this example, and deduce briefly whether it will lead to an equilibrium of allele frequencies or to fixation/loss of one of the alleles.
Question 3.
Describe briefly the following terms: a) Random genetic drift b) Genetically effective population size c) Founder effect d) Effective number of alleles e) Wahlund effect f) F
ST
(the formula based on heterozygosities in total- and sub-populations) g) Formula for F
ST
at equilibrium between immigration ( m ) and genetic drift h) Inbreeding coefficient ( f ) with definition i) The initial propability of fixation for a new mutant h) Gene flow, with the formula for the effect of immigration in one (1) generation on the allele frequency.
Question 4.
The body weight of lambs in a population shows a phenotypic mean of 54 kg with a standard deviation of 12.1 kg. The heritability h
2
is 0.45. a) Estimate V
A b) Assume that V
E
= 39.2. Estimate (V
D
+ V
I
).
Question 5. a) How are substitution rates estimated in coding DNA-sequences? b) Give some examples of the usage of such estimates.
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