The Hardy-Weinberg Principle Essential Learning Objectives 1.A.1 - - PowerPoint PPT Presentation

The Hardy-Weinberg Principle

Essential Learning Objectives 1.A.1 (g) and 1.A.1 (h)

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

Population and Gene Pool

• Population: A group of

individuals of the same species that live in the same area and interbreed, producing fertile

• ffspring
• Gene Pool: Consists of all copies
• f every type of allele at every

locus in all members of a population

What do you know about the Hardy-Weinberg Principle?

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

Hardy-Weinberg and the Punnett Square

Hardy-Weinberg Principle

• Used to assess whether natural selection or
• ther 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)

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

Conditions for Hardy-Weinberg Equilibrium

• 1. Large population size
• 2. Absence of migration (gene flow)
• 3. No mutations
• 4. Random mating
• 5. No natural selection

Are these conditions realistic?

Application of Hardy-Weinberg

• 1st – Determine what the genetic makeup of a

population would be if it were NOT evolving

• 2nd – Compare with the data that we actually
• bserve 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)

What do all those p’s and q’s mean???

Hardy-Weinberg Equations

p + q = 1 p2 + 2pq + q2 = 1

Hardy-Weinberg Equation

p = frequency of the dominant allele in a population q = frequency of the recessive allele in a population

p2 = frequency of homozygous dominant individuals 2pq = frequency of heterozygous individuals q2 = frequency of homozygous recessive individuals

Hardy-Weinberg Equation

Let’s 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?

Determine the frequency of the tan allele (p) and the frequency of the black allele (q):

Now determine the frequency of individuals that are homozygous dominant, heterozygous, and homozygous recessive:

p = 0.5 Tan (TT) = p2 = q = 0.5 Tan (Tt) = 2pq = Black (tt) = q2 =

Sample Problem – Cystic Fibrosis

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

• ther 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.

Sample Problem

p + q = 1 p2 + 2pq + q2 = 1

Calculate the allele frequencies (p and q):

• p represents the frequency of the recessive

allele (f) for cystic fibrosis

• q represents the frequency of the dominant

allele (F) for normal CFTR

Calculate the genotypic frequencies (p2, 2pq, q2):

About the Population (1700)

• How many people in the population are

carriers (heterozygous) for the cystic fibrosis gene?

Not so bad?