Hardy Weinberg Equilibrium

Hardy Weinberg Equilibrium

What is Hardy - Weinberg Equilibrium?

What is Hardy - Weinberg Equilibrium? It allows us to predict allele

frequencies in living populations The allele frequency tends to remain

the same from generation to generation unless acted on by outside influences.

In other words, we can predict what phenotypes/traits will be in a given population

It allows us to predict allele frequencies in living populations

The allele frequency tends to remain the same from generation to generation unless acted on by outside influences.

In other words, we can predict what phenotypes/traits will be in a given population

Hardy - Weinberg assumes that:

Hardy - Weinberg assumes that:

No net mutations occurIndividuals never enter or

leave a populationThe population is largeIndividuals mate randomlySelection does not occur

No net mutations occurIndividuals never enter or

leave a populationThe population is largeIndividuals mate randomlySelection does not occur

Misc. Info:Misc. Info:

“gene pool” = total genetic information in a population

Review: A = dominant alleleReview: a = recessive alleleReview: gametes = sperm,

egg

“gene pool” = total genetic information in a population

Review: A = dominant alleleReview: a = recessive alleleReview: gametes = sperm,

egg

Common Patterns of Inheritance

Common Patterns of Inheritance

Many populations follow a bell-shaped curve pattern

Consider fish length…Long fish = LLAverage length fish = LlShort fish = llMost samples show a smaller

amount of long & short fish, with more of them being average sized.

Many populations follow a bell-shaped curve pattern

Consider fish length…Long fish = LLAverage length fish = LlShort fish = llMost samples show a smaller

amount of long & short fish, with more of them being average sized.

Common Bell CurveCommon Bell Curve

Predicting Phenotype & Genetic Frequencies

Predicting Phenotype & Genetic Frequencies

Assume 100 fish in a population This means with 100 fish, 200 total alleles are

contributed. 4 are long (LL) So…there’s 8 “L” alleles 86 are average (Ll) So…there’s 86 more “L” alleles and 86 “l”

alleles 10 are short (ll) So…there’s 20 “l” alleles Therefore … 8 L’s + 86 L’s + 86 l’s + 20 l’s =

200 total alleles

Assume 100 fish in a population This means with 100 fish, 200 total alleles are

contributed. 4 are long (LL) So…there’s 8 “L” alleles 86 are average (Ll) So…there’s 86 more “L” alleles and 86 “l”

alleles 10 are short (ll) So…there’s 20 “l” alleles Therefore … 8 L’s + 86 L’s + 86 l’s + 20 l’s =

200 total alleles

Determining frequencies of alleles

Determining frequencies of alleles

There is a total of 94 “L”s out of 200

So … 94/200 = LThere is a total of 106 “l”s

out of 200.So … 106/200 = l

There is a total of 94 “L”s out of 200

So … 94/200 = LThere is a total of 106 “l”s

out of 200.So … 106/200 = l

The importance of p & qThe importance of p & q

No matter the allele letter, assign the dominant allele as letter “p”

No matter the allele letter, assign the recessive allele as letter “q”

The combinations of the p and q alleles must equal 100% of the population, so p + q = 1.

The probability of an “L” for the fish example is 94/200 or 0.47

The probability of an “l” for the fish example is 106/200 or 0.53

So… 0.47 + 0.53 = 1, or 100% of population

No matter the allele letter, assign the dominant allele as letter “p”

No matter the allele letter, assign the recessive allele as letter “q”

The combinations of the p and q alleles must equal 100% of the population, so p + q = 1.

The probability of an “L” for the fish example is 94/200 or 0.47

The probability of an “l” for the fish example is 106/200 or 0.53

So… 0.47 + 0.53 = 1, or 100% of population

So what does this mean to us??

So what does this mean to us??

There are LL genotypes There are Ll genotypes There are ll genotypes

So ….

LL = p2 Ll = 2pq ll = q2

Meaning … p2 + 2pq + q2 = 1 (or 100% of population

There are LL genotypes There are Ll genotypes There are ll genotypes

So ….

LL = p2 Ll = 2pq ll = q2

Meaning … p2 + 2pq + q2 = 1 (or 100% of population

Figure out the genotype frequencies …..

Figure out the genotype frequencies …..

Using the fish example, the probability of L = 0.47 and p represents the L allele

The probability of l = 0.53 and q represents the l allele

So, LL = (0.47)(0.47) = 0.2209 = p2

So, Ll = 2(0.47)(0.53) = 0.4982 = 2pq So, ll = (0.53)(0.53) = 0.2809 = q2

Therefore, 0.2209 + 0.4982 + 0.2809 = 1

Using the fish example, the probability of L = 0.47 and p represents the L allele

The probability of l = 0.53 and q represents the l allele

So, LL = (0.47)(0.47) = 0.2209 = p2

So, Ll = 2(0.47)(0.53) = 0.4982 = 2pq So, ll = (0.53)(0.53) = 0.2809 = q2

Therefore, 0.2209 + 0.4982 + 0.2809 = 1

Importance??Importance??

Genetic equilibrium is a theoretical state; factors can affect it.

By using H-W equilibrium, we can then consider what forces disrupt equilibrium

Forces that disrupt equilibrium drive natural selection.

Genetic equilibrium is a theoretical state; factors can affect it.

By using H-W equilibrium, we can then consider what forces disrupt equilibrium

Forces that disrupt equilibrium drive natural selection.