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Lecture

# Patterns of Selection

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School
Brock University
Department
Biology
Course
BIOL 2P92
Professor
Ingrid Makus
Semester
Fall

Description
(Pages 194 – 207) 6.3. Patterns of Selection: Testing Predictions of Population Genetic Theory Selection on Recessive and Dominant Alleles  This chapter covers the mathematics behind the evolution of populations. Read the book because I can’t explain numbers in words. Chapter 6 (Pages 210 – 218) 6.4 Mutation Adding Mutation to the Hardy – Weinberg Analysis: Mutation as an Evolutionary Mechanism  Mutation by itself is generally not a rapid mechanism of evolution. o For example in a population with a frequency of 0.9 for A alleles and a frequency of 0.1 for a alleles, a mutation rate of 1 per 10 000 (a high rate of mutation) would result in frequency of 0.89991 for the A allele and frequency of 0.10009 for the a allele.  This number is very similar to the original frequencies of alleles within that given population.  Therefore, it would take 1000 generations for the allele frequency for A to change from 0.9 to 0.81.  Mutation can cause substantial change in allele frequencies but it does slowly.  See Page 211 for clarification and the math shown Mutation and Selection  It is not correct to assume that mutation is unimportant because of its unappreciable changes in the allele frequencies of a population  Mutation combine with selection can become a crucial piece of the evolutionary process. o Read experiment on page 212 and 213. o The experiment shows that while mutation itself is only a weak mechanism of evolution, it nonetheless supplies the raw material on which natural selection acts. o Mutation is the ultimate source of genetic variation. Mutation-Selection Balance  Most mutations are deleterious.  Selection acts to eliminate such mutations from populations.  Deleterious alleles persist, however, because they are continually created anew.  When the rate at which copies of a deleterious alleles are being eliminated by selection is exactly equal to the rate at which new copies are beings created by mutation, the frequency of the allele is at equilibrium  mutation-selection balance.  What is the frequency of the deleterious allele at equilibrium? o ^q = √(µ/s) *The ^ should be on top of the q. o µ is the mutation rate and s is the selection coefficient (between 0 and 1) which
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