Deriving genotypic and allelic frequencies One definition of a population is its genotypic frequencies. This gives an indication of the genotypes which are the most or least prevalent in the population. The examples that will be used are for the blood type locus. Two alleles are possible, M or N, that can combine to give the following genotypes MM, MN, NN. The following data was collected from a human population. Genotype # of Individuals Genotypic frequencies MM 1787 MM = 1787/6129 = 29 MN 3039 MN = 3039/6129 = 50% NN 1303 NN = 1303/6129 = 21% Total 6129 The population that we just analyzed has just two alleles at the blood type locus, and each individual will have some combination of these two alleles. Thus, this entire population consists of 12,258 (6129 X 2) blood type alleles at the blood type locus. To deter mine the allelic frequencies we simply count the number of M or N alleles and divide by the total number of alleles. So the allelic frequency for the M allele will be: f(M) = [(2 x 1787) + 3039]/12,258 = 0.5395 and the frequency for the N allele will be: f(N) = [(2 x 1303) + 3039]/12,258 = 0.4605 By convention one of the alleles is given the designation P and the other q. Thus for the data we presented above, p=0.5395 and q=0.4605. Because we are analyzing all the alleles, the frequencies shoul d sum to 1.0 and p + q = 1. Furthermore, a population is considered by population geneticists to be polymorphic if two alleles are segregating and if the frequency of the most frequent allele is less than 0.99. The following quote from one of the classic books on quantitative genetics defines a population in a genetic perspective. The quote is from Introduction to Quantitative Genetics by D. S. Falconer, 1960, Ronald Press. "A population in the genetic sense, is not just a group of individuals, but a breeding group; and the genetics of a population is concerned not only with the genetic constitution of the individuals but also with the transmission of the genes from one gen eration to the next. In the transmission the genotypes of the parents are broken down and a new set of genotypes is constituted in the progeny, from the genes transmitted in the gametes. The genes carried by the population thus have continuity from gene ration to generation, but the genotypes in which they appear do not. The genetic constitution of a population, referring to the genes it carries, is described by the array of gene frequencies, that is by specification of the alleles present at every locu s and the numbers or proportions of the different alleles at each locus." The following example will illustrate how to calculate allelic frequencies from genotypic frequencies. It will also demonstrate that two different populations from the same species do not have to have the same allelic frequencies. Percent Location MM MN NN p q Greenland 83.5 15.6 0.9 0.92 0.08 Iceland 31.2 51.5 17.30 0.57 0.43 Let p=f(M) and q=f(N). Thus, p=f(MM) + Ѕ f(MN) and q=f(NN) + Ѕ f(MN). So the results of the above data are: for Greenland p=0.835 + Ѕ (0.156)=0.913 and q=0.009 + Ѕ (0.156)=0.087; and for Iceland p=0.312 + Ѕ (0.515)=0.569 and q=0.173 + Ѕ (0.515)=0.431. Clearly the allelic frequencies vary between these populations. Deriving Allelic Frequencies from Molecular Data Populations can also be scored with respect to loci scored with molecular probes. The above image displays the variability among humans at one specific locus. Each band can be considered to be an allele of the locus. No two individuals are the same i n this group. The individual whose DNA is found in lane 1 is homozygous. All of the others are heterozygous.. Individuals 2 and 8 share one allele, but differ at the other allele. Likewise individuals 3 and 10 share one allele, but are polymorphic at their second alleles. If a large number of individuals are scored with respect to this locus, then allelic frequencies for each allele (band) can be determined. Now lets score the allelic frequecies for a locus recognized by a molecular marker. The human population rep www.youtube.com
«The United States and European Reconstruction 1945-1960 (America in the 20th Century Series)» John Killick An accessible introduction to a key aspect in economic history--the impact of American financial intervention in Europe after World War II. Did "American dollars save the world"? Would Europe have revived itself after 1945? Was the Marshall Plan's creation of a coherent and prosperous western bloc critical for the outcome of the Cold War? Did American policy cause the substantial convergence in trans-atlantic productivity, incomes, and lifestyles? This analysis provides new and accessible answers to these important questions. Это и многое другое вы найдете в книге The United States and European Reconstruction 1945-1960 (America in the 20th Century Series) (John Killick). Напишите свою рецензию о книге John Killick «The United States and European Reconstruction 1945-1960 (America in the 20th Century Series)» http://izbe.ru/book/72491-the-united-states-and-european-reconstruction-1945-1960-america-in-the-20th-century-series-john-killick/