Lecture_24_DulaiS09_MicroEvolution

Lecture_24_DulaiS09_MicroEvolution - BIS 1 Lecture 23 1...

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Unformatted text preview: BIS 1 Lecture 23 1 Evolution Microevolutionary Process – Chapter 18 Lasthenia californica BIS 1 Lecture 23 2 Many Parts to Understanding Many Parts to Understanding Evolution Evolution • Change over time to the genetic material. • Best to understand each one first and then combine them… • MICROEVOLUTION – within species evolution. BIS 1 Lecture 23 3 Microevolution refers to the small-scale changes in allele frequencies in a population (gene pool) ( microevolution is studied by population biologists) You’ve seen how mutation can create new alleles. The mechanisms of evolution— natural selection , genetic drift , and gene flow — ALL change allele frequencies in a population’s gene pool BIS 1 Lecture 23 4 Example… • Fruit fly • Real experiments • 20 hours without food • 80/20 rule • 62 hours without food BIS 1 Lecture 23 5 hat do we mean by ‘allele frequencies’ in a population? CONSIDER: A (small) population of 10 ( diploid ) individuals. Let’s focus one allele; A in chromosome 1 of this population (note that this is called a locus ; for instance a population geneticist would study the frequency of different alleles at locus A). A A A A A A A A A A A a A a A a A a a a 20 total chromosomes in the 10 individuals of this population BIS 1 Lecture 23 6 Frequencies • In statistics, the total of a frequency may be expressed as a percentage – All the people in this room = 100% • Or as a fraction – Where the total is always 1.00 – Number of boys = 0.5 – Number of girls = 0.5 BIS 1 Lecture 23 7 What is the frequency of each allele (A vs. a) at this locus in the population ? A A A A A A A A A A A a A a A a A a a a 5 homozygotes AA 4 heterozygotes Aa 1 homozygote aa f A = (5x2) + 4 20 f a = (1x2) + 4 20 = 0.7 = 0.3 This is just counting up A’s and a’s. Note f A +f a =1. BIS 1 Lecture 23 8 The key question is: What is the frequency of each allele at this locus in the gametes (at the end of this generation)? f A = f a = 0.7 0.3 TAKE AS GIVEN The allele frequencies in the gametes should be identical to the allele frequencies in the population. BIS 1 Lecture 23 9 Notion of genetic equilibrium at a locus Genetic equilibrium is when allele frequencies stay the same from one generation to the next (in our example, f A =0.7, f a =0.3 ) Genetic equilibrium implies no evolution at that locus. BIS 1 Lecture 23 10 AA ( p 2 ) Aa ( pq ) Aa ( pq ) A p a q A p a q aa ( q 2 ) If this locus is at genetic equilibrium , then we can predict the genotype frequencies found in the next generation. They are given by the Hardy-Weinberg equation : p 2 AA + 2 pq Aa + q 2 aa = 1 Frequency of allele Frequency of allele A A = = p Frequency of allele Frequency of allele a = = q The Hardy-Weinberg equation is derived (quite simply) from a Punnet square BIS 1 Lecture 23 11 490 AA dark-blue wings 420 Aa medium-blue wings...
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This note was uploaded on 11/18/2010 for the course SS 101 taught by Professor Denver during the Spring '10 term at Alabama.

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Lecture_24_DulaiS09_MicroEvolution - BIS 1 Lecture 23 1...

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