Evolution: Hardy-Weinberg equilibrium

• Biologie
• Middelbare school
• vwo
• Leerjaar 4

Evolution

Chapter 12&13 

Lesson 4: Hardy-Weinberg equilibrium

Learning objectives

• You can distinguish between allele frequency, genotype frequency, gene, allele and gene pool
• You can explain the requirements necessary for a population to meet the Hardy-Weinberg equilibrium
• You can use the Hardy-Weinberg equations to perform calculations on population genetics

Gene

Allele

Phenotype

Genotype

Gene pool

Version of a gene

All copies of a gene in a population

Section of DNA that controls a particular trait

Set of alleles

Observable features

1

2

3

1: two W alleles

2: one W allele and one w allele

3: two w alleles

Total number of alleles?
Number of W?
Number of w?

Total: 18

W: 13

w: 5

Allele frequency

Calculate allele frequency of W and the allele frequency of w

Total: 18

W: 13

w: 5

Allele frequency

Allele frequency of W:13/18=0,72

Allele frequency of w: 5/18=0,28

                      Total=1,00

Make sense?

Allele frequency formula

We assign p to the dominant allele

We assign q to the recessive allele

Result:

p + q = 1

What is represented by the letter q?

1. the gene pool
2. the dominant allele
3. the recessive allele
4. the genotype

If p= 0,7, q is?

1. 0,3
2. 1,0
3. 0,2
4. 0,7

If the frequency of the dominant allele is 0,6, the frequency of p is?

1. 1,0
2. 0,4
3. 0,5
4. 0,6

Genotype frequency

• Frequency WW?
• Frequency Ww?
• Frequency ww?

Genotype frequency

Usually more interesting

• Frequency WW?:
  6/9=0,67
• Frequency Ww?
  1/9=0,11
• Frequency ww?
  2/9=0,22

Calculate chance of genotype WW

= W

= w

1. Frequency W in population
2. Frequency = chance to 'pull'
3. Chance to pull WW = chance to pull W x chance to pull W

Calculate chance of genotype WW

= W

= w

1. Frequency W in population
2. Frequency = chance to 'pull'
3. Chance to pull WW = chance to pull W x chance to pull W

Frequency W = 0,7

Chance WW = 0,7 x 0,7 =0,49

A population of 150 individuals has an allele frequency of 0,6 for the dominant allele (B) and a frequency of 0,4 for the recessive allele (b). Use the Hardy-Weinberg equation to determine the frequency of the genotype (bb).

1. 0,36
2. 0,4
3. 0,16
4. 0,24

Turning it into p and q

If WW is W x W, how do you write it using p?

If ww is w x w, how do you write it using q?

Turning it into p and q

If WW is W x W, how do you write it using p?

If ww is w x w, how do you write it using q?

p x p = p2

q x q = q2

How would you calculate the chance of a heterozygote?

Turning it into p and q

How would you calculate the chance of a heterozygote?

Calculating genotype frequencies

Homozygous dominant: p x p = p2

Heterozygous: p x q + q x p = 2pq

Homozygous recessive: q x q = q2

In total:

p2 + 2pq + q2 = 1

Total is 1 because together they make up all genotypes

q2 is the frequency of:

1. the recessive allele
2. the dominant allele
3. the recessive genotype
4. the dominant genotype

p=0,2. What is the frequency of the recessive phenotype?

1. 0,04
2. 0,4
3. 0,32
4. 0,64

Give the frequencies

Hardy-Weinberg equilibrium

p+q=1 and p2+2pq+q2=1 are formulas that belong to the Hardy-Weinberg equilibrium.

They are used to track allele frequencies and see if they chance/ make predictions about and how they will change.

If a population is in a Hardy-Weinberg equilibrium this means the allele frequencies are not changing. Therefore, there is no evolution! 

Equilibrium only exists if these five requirements are met

Remember the five fingers of evolution?

What if requirements are not met?

Evolution!

A population's recessive allele frequency is 25%. What is the percentage of the Homozygous Dominant genotype?

64% of the population has the recessive phenotype. What is the percentage of the heterozygous genotype?

Homework

Worksheet Hardy-Weinberg on Classroom