What Darwin didn’t Get  Darwin couldn’t 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 populations So 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 EQUILIBRIUM

THE BIG SEVEN 1.Mutation is not occurring 2.Natural selection is not occurring 3.The population is very large 4.All members of a population breed 5.All mating is totally random 6.Everyone produces the same number of offspring 7.There is no immigration or emigration happening in the population

Ok, so how realistic is this??? Not very, but we can use an equation as a model for population genetics First 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 Recessive Dominant Recessive The alleles are represented as letters Capital letter = Dominant Lowercase Letter = Recessive AA aa Aa

 AA is called: HOMOZYGOUS DOMINANT  Aa is called: HETEROZYGOUS DOMINANT  aa is called: HOMOZYGOUS RECESSIVE

The HARDY- WEINBERG Equation (s) p + q = 1 p 2 + 2pq + q 2 = 1 BREATH DEEP….here we go…… These equations figure out: ALLELE FREQUENCY GENOTYPE FREQUENCY

AA + Aa + aa = 1 p 2 + 2pq + q 2 = 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 given That the characteristic is either DOMINANT or RECESSIVE Example: the problem will tell you that RED = R WHITE = r

THEN you will be GIVEN A VALUE of one of these: A a AA aa And you already know that: A = p a = q AA = p 2 Aa = 2 pq aa = q 2

NOW all you have to do is.. Plug the values in!!! But it’s kind of like a maze Sooooooooo

STEP 1 : write out both formulas AA + Aa + aa = 1 p 2 + 2pq + q 2 = 1 AND A + a = 1 p + q = 1

Step 2 : Figure out what you’ve been given and plug it in

Example: if you are given the value of aa as 50% or.5o Plug.50 into the q 2 spot AA + Aa + aa = 1 p 2 + 2pq + q 2 = 1 p 2 + 2pq +.50 = 1 Now you can figure out q.50 =.71

A + a = 1 p+ q = 1 P +.71 = = 1 AA + Aa + aa = 1 p 2 + 2pq + q 2 = (.29)(.71) +.50 = = 1

Lets look at a problem The 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: We’re looking or GENE FREQUENCY Intelligent = A Aggressive = a Homozygous recessive = aa = 25% =.25 Heterozygous = Aa