The Hardy-Weinberg Principle. Essential Learning Objectives 1.A.1 (g) and 1.A.1 (h)

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1 The Hardy-Weinberg Principle Essential Learning Objectives 1.A.1 (g) and 1.A.1 (h)

2 Evolution of Populations Individuals do not evolve, but rather, populations evolve Scientists use mathematical models to study evolutionary changes in allele frequencies within a population

3 Population and Gene Pool Population: A group of individuals of the same species that live in the same area and interbreed, producing fertile offspring Gene Pool: Consists of all copies of every type of allele at every locus in all members of a population

4 Hardy-Weinberg Principle Used to assess whether natural selection or other factors are causing evolution of a population (a change in the frequency of alleles in a population) Used to make predictions for populations (like a Punnett square is used to make predictions about individuals)

5 Hardy-Weinberg and the Punnett Square

6 Hardy-Weinberg Principle States that allele frequencies in a population should remain constant unless one or more factors cause those frequencies to change Mathematical equation is used to test whether a population is evolving

7 Five Conditions for a Population to be in Hardy-Weinberg Equilibrium (NOT evolving)

8 Conditions for a Population to Remain in Hardy-Weinberg Equilibrium 1. Large population size (small populations are more susceptible to genetic drift) 2. Absence of migration (also known as gene flow) 3. No mutations 4. Random mating (meaning no sexual selection) 5. No natural selection Are these conditions realistic?

9 Application of Hardy-Weinberg 1 st Determine what the genetic makeup of a population would be if it were NOT evolving 2 nd Compare with the data that we actually observe for the population in subsequent generations Can be used to identify variables that are influencing evolution of a population (such as natural selection or genetic drift)

10 Hardy-Weinberg Equations p + q = 1 p 2 + 2pq + q 2 = 1

11 What do all those p s and q s mean???

12 Hardy-Weinberg Equation p + q = 1 p = frequency of the dominant allele for a particular gene in a population q = frequency of the recessive allele for a particular gene in a population

13 Hardy-Weinberg Equation p 2 + 2pq + q 2 = 1 p 2 = frequency of homozygous dominant individuals within a population 2pq = frequency of heterozygous individuals within a population q 2 = frequency of homozygous recessive individuals within a population

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15 Now Try It! In a pig population, tan pigs (T) are dominant to black pigs (t) What are the possible genotypes for tan pigs and black pigs?

16 Determine the frequency of the tan allele (p) and the frequency of the black allele (q): (Hint you will need to count the total number of pigs in the population)

17 Now determine the frequency of individuals that are homozygous dominant, heterozygous, and homozygous recessive: p = 0.5 Tan (TT) = p 2 = q = 0.5 Tan (Tt) = 2pq = Black (tt) = q 2 =

18 Sample Problem Cystic Fibrosis

19 Sample Problem Cystic fibrosis is a recessive genetic disorder in which a defective gene (CFTR) causes a thick, buildup of mucus in the lungs, pancreas and other organs. 1 in 1700 U.S. Caucasian newborns have cystic fibrosis. Use F for the normal allele which is dominant to the cystic fibrosis allele, f.

20 Sample Problem p + q = 1 p 2 + 2pq + q 2 = 1

21 Calculate the allele frequencies (p and q): p represents the frequency of the dominant allele (F) for cystic fibrosis q represents the frequency of the recessive allele (f) for normal CFTR

22 Calculate the genotypic frequencies (p 2, 2pq, q 2 ):

23 About the Population (1700) How many people in the population are carriers (heterozygous) for the cystic fibrosis gene?

24 Not so bad?