ch. 27 a

# ch. 27 a - Chapter 27: Population genetics Definitions...

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Chapter 27: Population genetics Definitions Population - group of individuals sharing a common set of genes, occupying the same area, and can interbreed. Population genetics - the distribution of genes in populations and how the frequencies of genes and genotypes are maintained or changed over time. Allelic frequency - measurement of the proportion of the individuals in a population carrying a particular allele. Phenotype frequency - measurement of the proportion of total individuals in a population that express a given trait or phenotype. Genotype frequency - measurement of the proportion of total individuals in a population that carry a particular genotype.

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# of copies of an allele in a population Allelle frequency = total # of alleles for that gene in a population # of individuals with a particular genotype in a population Genotype frequency = total # of individuals in a population 64 tall plants TT , 32 tall plants Tt and 4 dwarf plants tt Calculate allele frequency t = = = 32 + 2(4) 2(64) + 2(32) + 2(4) 40 200 0. 2 Allelle frequency of t is 20% Calculate genotype frequency of tt (dwarf) plants = = 0. 04 4 64 + 32 + 4 4 100 Genotype frequency of dwarf plants in the population is 4%
200 32 + 2(4) 2(64) + 2(32) + 2(4) Allelle frequency of t is 20% 64 tall plants TT , 32 tall plants Tt and 4 dwarf plants tt Allelic frequencies can be calculated from (1) the number of or (2) the frequency of the genotypes. From the number of genotypes (# of copies of particular allele divide by total # of all alleles) For a locus with only 2 alleles the frequency of the alleles are represented by symbols p and q. p = f ( A ) = where n AA , n Aa and n aa represent AA , Aa , and aa individuals and N is total number of individuals. Divide by 2N because each diploid individual has 2 alleles at a locus. p + q = 1 q = f ( a ) = Calculate allele frequency t = = = From the genotype frequency Add the frequency of the homozygote to half the frequency of the heterozygote (because half the heterozygote’s alleles are of each type). t

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## This note was uploaded on 10/07/2009 for the course BIOLOGY 2203 taught by Professor Anthwal during the Fall '08 term at Temple.

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ch. 27 a - Chapter 27: Population genetics Definitions...

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