Hardy-Weinberg Equilibrium

Hardy-Weinberg Equilibrium

What Darwin didnt Get Darwin couldnt figure out why there was so much GENETIC VARIATION in natural populations.

Darwin thought that selection should ALWAYS favor the optimal form and eliminate vaiation hmmm. But.

The reality is, there is A LOT of variation in populationsSo how could this be?Hardy and Weinberg (1908) Independently solved WHY this genetic variation exists

Hardy was a mathematician

Weinberg was a physician

They showed that the frequency of genotypes in a population will stay the same from one generation to the next.

That is if : SEVEN conditions are met

We call this HARDY-WEINBERG EQUILIBRIUMTHE BIG SEVENMutation is not occurring

Natural selection is not occurring

The population is very large

All members of a population breed

All mating is totally random

Everyone produces the same number of offspring

There is no immigration or emigration happening in the populationOk, so how realistic is this???Not very, but we can use an equation as a model for population geneticsFirst you need to know that:

ALLELES represent GENES

Individuals receive one allele from each parent

This makes up an individuals genes

The genes determine the phenotype

Therefore an individual will receive a combination of alleles in the form of :

Dominant Dominant

Recessive Recessive

Dominant Recessive

The alleles are represented as letters

Capital letter = DominantLowercase Letter = Recessive

AAaaAa

AA is called: HOMOZYGOUS DOMINANT

Aa is called: HETEROZYGOUS DOMINANT

aa is called: HOMOZYGOUS RECESSIVE

The HARDY- WEINBERG Equation (s)

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

BREATH DEEP.here we goThese equations figure out:

ALLELE FREQUENCY

GENOTYPE FREQUENCY

AA + Aa + aa = 1p2 + 2pq + q2 = 1

Formula for GENOTYPE Frequency

A + a = 1 p + q = 1

Formula for ALLELE frequency

Now that we know what each formula represents, figuring out each problem is easy!!!!!!You will ALWAYS be givenThat the characteristic is either DOMINANT or RECESSIVE

Example: the problem will tell you that

RED = RWHITE = rTHEN you will be GIVENA VALUE of one of these:

A a AA aa

And you already know that:

A = p a = q AA = p2 Aa = 2pq aa = q2

NOW all you have to do is..Plug the values in!!!

But its kind of like a maze

Sooooooooo STEP 1: write out both formulas

AA + Aa + aa = 1p2 + 2pq + q2 = 1

AND

A + a = 1 p + q = 1

Step 2: Figure out what youve been given and plug it in

Example: if you are given the value of aa as 50% or .5o

Plug .50 into the q2 spot

AA + Aa + aa = 1p2 + 2pq + q2 = 1p2 + 2pq + .50 = 1

Now you can figure out q

.50=.71A + a = 1p+ q = 1

P + .71 = 1.29 + .71 = 1

AA + Aa + aa = 1p2 + 2pq + q2 = 1

.084 + 2 (.29)(.71) + .50 = 1.084 + .41 + .50 = 1

Lets look at a problemThe gene for an intelligent dolphin is dominant to a gene for an aggressive dolphin. In a population there are 25% that have the gene for homozygous recessive aggressiveness. Figure out the gene frequency for the heterozygous intelligent. OK, so we know that:

Were looking or GENE FREQUENCY

Intelligent = A

Aggressive = a

Homozygous recessive = aa = 25% = .25

Heterozygous = Aa