Chapter 25__upload_Genetics of Populations

Flower color is red pink or white and controlled by 2

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Unformatted text preview: , or white and controlled by 2 alleles at a single gene (I and i). With II=red, Ii=pink, ii=white Suppose we sample 400 individuals in a population: 165 were red (I/I) 190 were pink (I/i) 45 were white (i/i) Calculating Allele Frequencies Calculating Allele frequency of white (i) allele: Other populations of this plant my have different allele frequencies Calculating Allele Frequencies Calculating Allele frequency of (I) allele: NOTE: Frequencies of the two alleles should add to 1.0. In other words p + q=1.0 From Genotypes (400 individuals) From 165 400 = 0.413 190 400 = 0.475 (I/i) 45 400 = 0.113 (I/I) (i/i) 1 0.113 + (0.475) = 0.35 2 Calculating Allele Frequencies Sample problem: Suppose we sample 196 individuals in a population: 75 were (AA) 26 were (Aa) 95 were (aa) What are the frequencies of the A and a alleles? Calculating Allele Frequencies What if population contains 3 or more alleles? Suppose we sample 236 individuals in a population: 36 were (A1A1) 29 were (A1A2) 67 were (A2A2) 54 were (A2A3) 50 were (A3A3) What are the frequencies of the A1, A2, A3 alleles? What are the genotype frequencies? Calculating Allele Frequencies Sex-linked loci XX, XY; ZZ, ZW – occur in different doses in females and males. – Butterfly example: Males Females ZF ZF ZFZS ZS ZS Total ZF W ZS W total 39 46 27 112 29 33 62 Frequency of ZF = Why calculate allele frequencies? -provides information on the diversity present in natural populations! What is genetic diversity? Genetic diversity is the variety of alleles and genotypes present in organisms. GD can be detected via morphological variation – eye color – or genetic variation – protein or DNA variation – and can results in many different forms or behaviors. Genetic Diversity and its relation to… Evolution – a change in the genetic composition of a population ­ only occurs when there is genetic diversity What processes cause allele frequencies to change? IMPORTANCE OF GENETIC DIVERSITY: Environmental change is a continuous process and genetic diversity is required for populations to evolve to adapt to such change Reasons why the ability to change is relevant: a. Global warming b. Habitat destruction c. Pesticide/Herbicide use d. Introduction of novel competitors IMPORTANCE OF GENETIC DIVERSITY: Examples of species’ response to environmental change. Industrial melanism – The peppered moth, Biston betularia, is generally a mottled light color, called typical, but in a number of areas of England, a dark melanic form is common. The melanic moths have increased because their dark color serves as protective camouflage from bird predation in the polluted areas they inhabit Changes in allele frequency Must understand how alleles behave in populations Develop a null model for behavior of genes in populations Model specifies what will happen to frequencies of alleles and genotypes Applies to all diploid sexual organisms How Can We Quantify and Track Genetic Variation in Populations? Populations? Theoreti...
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This document was uploaded on 09/17/2013.

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