Download File - Biology with Radjewski

Hardy Weinberg
What the heck is that?
Let’s review Evolution
• What is a gene pool?
• includes all the alleles for all the genes present
in the population
• So what does this mean?
• Means we can calculate different types of
frequencies
Suppose for example, that there are
1000 people in a population and they
have the following genotypes for a
trait:
Genotype
AA
Aa
aa
Total:
Number
490 people
420 people
90 people
1000 people
What is the genotype frequency?
Genotype
AA
Aa
aa
Total:
Number
490 ppl
420
90
1000
•
•
•
•
490/1000 = 0.49
420/1000 = 0.42
90/1000 = 0.09
Add all the
genotype
frequencies up
and they should
equal 1.0.
What is the phenotype frequency?
Genotype
AA
Aa
aa
Number
490 ppl
420
90
There are 2 phenotypes
Dominant
Recessive
How many dominant individuals are there?
490 + 420 = 910
How many recessive individuals are there?
90
• 910/1000 = 0.91
• 90/1000 = 0.09
• Equals 1.0
What is the allele frequency?
Genotype
AA
Aa
aa
Number
490 ppl
420
90
• 1400/2000 = 0.7
• 600/2000 = 0.3
• Total is 1.0
There are 2 alleles
A
a
So how many individuals
have A?
How many
individuals have a?
490+490+420 = 1400
420 + 90 + 90 = 600
Do you think these frequences
(genotype, phenotype and
allelic) would change over time?
Yes, if evolution was occurring
WOULD NOT
These frequencies _________
change if the population was in
genetic equilibrium.
So these 2 guys, Hardy and
Weinberg got together and said
that if certain conditions are kept
constant, large populations will not
change their frequencies.
• So what are these
conditions?
Five conditions are:
•
•
•
•
•
Random mating – no selection of mates
No net mutations
Large population size
No migration (immigration or emigration)
No natural selection – no favoring of
phenotypes
The best thing about Hardy
Weinberg is
It can be represented
mathematically! And I know how
much you guys LOVE math 
Symbols to memorize
• P = frequency of dominant allele (A)
• Q = frequency of recessive allele (a)
• And P+Q = 1; why?
• Because all students in the population are
either dominant or recessive
Equations to memorize
• P2 = frequency of homozygous dominant (AA)
• 2pq = frequency of heterozygous dominant
(Aa)
• Q2 = frequency of the recessive (aa)
• Also, P2 + 2pq + Q2 = 1; why?
• Because all people fall in one of those 3
groups above
So from our example earlier,
Genotype
AA
Aa
aa
Number
490 ppl
420
90
•
•
•
•
0.09
What is Q2?
What is Q? 0.3
What is P? 0.7; remember p+q=1
Does P + Q =1 in this 0.7+0.3 = 1;
yes
example?
• What is P2? P = 0.7, so (0.7)2 = 0.49
• What is 2pq? 2(0.7)(0.3) = 0.42
• Does , P2 + 2pq + Q2 = 1
in this example? 0.49 + 0.42 +
0.09 = 1; yes