Terms: Population: Group of interbreeding or potentially interbreeding organisms Population Genetics: Branch of genetics that studies the genetic makeup of groups and how the group’s genetic composition changes over time. Microevolution: evolution at the genetic level

Terms Cont. Gene Pool: Total genetic information in a population at one time; all the alleles in the population Ex. The genotypes of a certain population are below: AA = 45Aa= 35aa= 20 In the gene pool there are 125 (A) alleles and 75 (a) alleles in this gene pool. Population Geneticists: study how we get from the gene pool now to the gene pool in the future through microevolution

Gene Pool Allele frequency Phenotype frequency Genotype frequency

Allele Frequency f(A) = (2n AA + n Aa )/ 2N this is symbolized by the letter p f(a) = (2n aa + n Aa )/2N this is symbolized by the letter q Where n AA = number of homozygous dominant individuals n Aa = number of heterozygous individuals n aa = number of homozygous recessive individuals N = number of organisms in the population Ex. Aa- One A and one a

Allele Frequency Calculations in a Gene Pool: AA=50Aa=20aa=30 Calculate the genotypic and allelic frequencies from the numbers above.

Practice Problem The genotypic numbers of a population of bears is below. Calculate the genotypic and allelic frequency for this gene pool: BB – 34Bb- 56bb- 16

Predicting Phenotypes You can use alleleic frequencies and probability rules to predict future phenotypic and genotypic ratios. What would expect the phenotypic ratios to be of the next generation?

Allele Frequency Although four o’clock flowers differ phenotypically from generation to generation, the allele frequencies tend to remain the same.

The Hardy-Weinberg Genetic Law The primary goal of population genetics is to understand the process that shapes a population’s gene pool. First we must know what effect reproduction has on genotypic and allelic frequencies. The Hardy-Weinberg Law allows us to model the effect of reproduction of the two frequencies.

The Hardy-Weinberg Genetic Law The Law is actually a mathematical model that allows us to see the effect of reproduction on genotypic and allelic frequencies. It makes several assumptions about the population and provides two key predictions if the assumptions are met. Large, random mating populations No genetic drift No selection No mutation No migration

Uses for Hardy-Weinberg Equation Test for change in gene pool Estimate the frequency and number of carriers in a dominant/recessive trait Basis for modeling Mechanisms of Gene Pool change

Example of Problems Is a population in Hardy-Weinburg equilibrium? How many carriers are found in a population?

To find if a population is in equilibrium: Find allele frequencies (p and q) Find expected genotypic frequencies Find expected genotypic counts Run a Chi-Square Test (Less than 3.84)

Chi-Squared Equation O= Observed ValuesE=Expected Values Sigma= “The Addition of All”

Example Problem A population has the following genotypes SS: 57SC: 169CC: 29 Is this population in Hardy-Weinberg Equilibrium?

Other example In a population of 400 individuals 300 express the dominant phenotype. How many heterozygous individuals (carriers) would you expect?

Practice Problems Two scientist working at Glacier Lake, Colorado discovered three genotypes (RR, Rr, rr) at a locus in some weird pine tree. The observed numbers were: RR135 Rr44 rr11 Do the trees show Hardy-Weinberg Equilibrium at this locus?

Practice Problems Cystic Fibrosis is a recessive disorder that is found in approximately 1 out of every 2000 people. Assuming the population is in Hardy- Weinberg what percentage of people are carriers of the disorder.