population_genetics

b. From genotypic proportions.
p= f(A)=(Frequency of the AA homozygote) + (1/2)(frequency of the Aa heterozygote) p= f(a)=(Frequency of the aa homozygote) + (1/2)(frequency of the Aa heterozygote)
Assumptions of the Hardy-Weinberg Law
1. This law is a simplification of complex events. There are certain assumptions that must be present for the law to apply:
Predictions of the Hardy-Weinberg Law
1. If the conditions are met, the population will be in genetic equilibrium, with two expected results:
a. Allele frequencies do not change over generations, so the gene pool is not evolving at the locus under study. b. After one generation of random mating, genotypic frequencies will be p2, 2pq and q2, and will stay constant in these proportions as long as the conditions above are met. This is Hardy-Weinberg equilibrium, which allows predictions to be made about genotypic frequencies.
Allelic Frequencies
1. Allelic frequencies give more information about the structure of the population than genotypic frequencies.
Allelic Frequency= No. of copies of a given allele / Sum of counts of all alleles in the population
Population Genetics
PhD Candidate: Zhang Lu Computer Science, CityU of HongKong
Introduction
1. Population genetics is the field of genetics that studies heredity in groups of individuals for traits that are determined by one, or only a few genes. 2. Both Population and Quantitative Genetics use Mendelian principles. 3. These areas of genetics have been important in the fusion of Mendelian theory with Darwinian theory to create the neo-Darwinian synthesis that underlies much of current biological thinking. 4. Population geneticists study the genetic structure of populations, and how they change geographically and over time. 5. A Mendelian population is a group of interbreeding individuals who share a common set of genes. The total of all alleles in the population constitutes the gene pool. 6. Modern molecular biology techniques have allowed for rapid advancement in population genetics. 7. Statistical models are often developed in population genetics. The Hardy-Weinberg law is a major example.
Genetic Structure of Populations Genotypic Frequencies
1. Genotypic frequencies are a way to study the genes in a particular gene pool by quantifying the genotypes (pairs of alleles) at a given locus. 2. To calculate genotypic frequency, count individuals with one genotype, and divide by total individuals in the population. Repeat for each genotype in the population. 3. A frequency is a proportion with a range of 0–1. If 43% of population has a trait, the frequency of that trait is 0.43. For any given trait, the sum of the genotypic frequencies in a population should be 1. Spot patterns on the moth Panaxia dominula are an example.
1. Often more than two alleles are possible at a given locus, and the frequencies of possible genotypes are still given by the square of the allelic frequencies. If three alleles are present (e.g., alleles A, B and C) with frequencies p, q, and r, the frequencies of the genotypes at equilibrium will be:
The Hardy-Weinberg Law
1. This is a simple explanation showing how Mendelian segregation influences allelic and genotypic frequencies in a population. 2. There are three parts to the law: one set of assumptions and two major results.
Fig. 22.3 Relationship of the frequencies of the genotypes AA, Aa, and aa to the frequencies of alleles A and a in populations in Hardy-Weinberg equilibrium
Derivation of the Hardy-Weinberg Law
1. Zygotes are formed by random combinations of alleles, in proportion to the abundance of that allele in the population. 2. When a population is in equilibrium, genotypic frequencies will be in the proportions p2, 2pq and q2. This results from the expansion of the square of the allelic frequencies: (p + q)2 = p2 + 2pq + q2. 3. Mendelian principles acting on a population in equilibrium will work to maintain that equilibrium.
3.
Allelic frequencies at an X-linked locus are more complex because one sex will have only one X-linked allele while the other has two.
p=f(XA)=((2 x XAXA females) + (1 x XAXa female) + (1 x XAY male)) / ((2 x number of females)+ (1 x number of males)) p=f(Xa)ห้องสมุดไป่ตู้((2 x XaXa females) + (1 x XAXa female) + (1 x XaY male)) / ((2 x number of females)+ (1 x number of males))