Transcript Is the Hardy-Weinberg principle a realistic model to

Sponge: Set up Cornell Notes on pg. 55
Topic: 5.4 Evolution: Hardy-Weinberg Principle
Essential Question: Is the Hardy-Weinberg
principle a realistic model to use to study
evolution?
5.4 Evolution: Hardy-Weinberg Principle
Is the Hardy-Weinberg principle a realistic model to
use to study evolution?
Key Vocabulary:
Hardy-Weinberg Principle
BIOZONE: 238-251 due Wed11/05
BIOZONE: 238-251 due Wed 11/05
The Hardy-Weinberg Principle
Hardy-Weinberg Principle: is used to predict genotype frequencies in a
population
• States that allelic frequencies will remain the same from generation to
generation assuming five conditions are met (below)
• Describes populations that are NOT evolving
• This principle is important because it gives biologists a standard from which
to measure changes in allele frequency in a population.
The Hardy-Weinberg Principle
Allele frequencies will remain the same
from generation to generation assuming
five conditions are met:
1. Very large population: no genetic
drift.
In each generation, some individuals may, just by
chance, leave behind a few more descendants
(and genes, of course!) than other individuals.
The genes of the next generation will be the
genes of the “lucky” individuals, not necessarily
the healthier or “better” individuals.
2. No emigration or immigration: no
gene flow. No organisms coming or
going into the population.
The Hardy-Weinberg Principle
3. No mutations: No new alleles added to gene pool.
4. Random mating: No sexual selection. They will mate with any
female/male.
5. No natural selection: All traits aid equally in survival. No traits are
better than others.
Real populations rarely
meet all five conditions!!!
The Hardy-Weinberg Equation
• In order to calculate the frequencies of alleles, genotypes, or phenotypes
within a population the Hardy-Weinberg equation is needed
• Useful in determining how fast a population is changing or in predicting the
outcomes of matings or crosses
• Values predicted by the equation are those that would be present if the population is
in equilibrium.
• The Hardy-Weinberg equation is based on Mendelian genetics. It is derived
from a simple Punnett square in which p is the frequency of the dominant
allele and q is the frequency of the recessive allele.
The Hardy-Weinberg Equation
2 (pxq)
The Hardy-Weinberg Example
BB(p²)= 36% of population is homozygous dominant
Bb (2pq)= 48% of population is heterozygous
Bb (q²)= 16% of population is homozygous recessive
Freq of B allele?
Freq of b allele?
How to find allele frequencies:
p+q=1
p= dominant allele frequency
q= recessive allele frequency
How can I find p if I know p²?
• Use the square root!
• √ of p² = p
How to find allele frequencies:
p+q=1
• p= the frequency of the dominant allele (B) (p+ ½ 2pq)
• q= frequency of the recessive allele (b) (q+ ½ 2pq)
• Must add up to 1
p= .36+.24=.60
q= .24+.16=.40
.60 + .40 = 1
The Hardy-Weinberg Principle Practice
Albinism is a rare genetically inherited trait that is only expressed in the phenotype of
homozygous recessive individuals (aa). The most characteristic symptom is a marked deficiency in the skin
and hair pigment melanin. This condition can occur among any human group as well as among other animal
species. The average human frequency of albinism in North America is only about 1 in 20,000.
Referring back to the Hardy-Weinberg equation (p² + 2pq + q² = 1), the frequency of homozygous recessive
individuals (aa) in a population is q².
Therefore, in North America the following must be true for albinism: q² = 1/20,000 = .00005
Figure out the predicted frequency of homozygous individuals,
heterozygous individuals, and homozygous recessive
individuals. (HINT: Find the square root of q² to find q.)
Referring back to the Hardy-Weinberg equation (p² + 2pq + q² = 1), the frequency of homozygous recessive
individuals (aa) in a population is q².
Therefore, in North America the following must be true for albinism: q² = 1/20,000 = .00005
Figure out the predicted frequency of homozygous individuals, heterozygous individuals, and homozygous
recessive individuals. (HINT: Find the square root of p2 to find p.)
p² + 2pq + .00005
Sq. root of .00005= .007
p + q= 1
p + .007= 1
1-.007= p
.993 + .007= 1
p= .993
q= .007
Referring back to the Hardy-Weinberg equation (p² + 2pq + q² = 1), the frequency of homozygous recessive
individuals (aa) in a population is q².
Therefore, in North America the following must be true for albinism: q² = 1/20,000 = .00005
Figure out the predicted frequency of homozygous individuals, heterozygous individuals, and homozygous
recessive individuals. (HINT: Find the square root of p2 to find p.)
p2 + 2pq + .00005
Sq root of .00005= .007
p + q= 1
p + .007= 1
1-.007= p
.993 + .007= 1
p= .993
q= .007
Now let’s input this information
into the Hardy-Weinberg
equation: (p² + 2pq + q² = 1)
 p²=
 2pq=
 q²=
Referring back to the Hardy-Weinberg equation (p² + 2pq + q² = 1), the frequency of homozygous recessive
individuals (aa) in a population is q².
Therefore, in North America the following must be true for albinism: q² = 1/20,000 = .00005
Figure out the predicted frequency of homozygous individuals, heterozygous individuals, and homozygous
recessive individuals. (HINT: Find the square root of p2 to find p.)
p2 + 2pq + .00005
Sq root of .00005= .007
p + q= 1
p + .007= 1
1-.007= p
.993 + .007= 1
p= .993
q= .007
Now let’s input this information
into the Hardy-Weinberg
equation: (p² + 2pq + q² = 1)
p²= .986
2pq= .014
q²= .00005
 Change to %s to find the
frequency for each in the
population
p²= predicted freq. of homozygous dominant
individuals= .986….98.6%
2pq= predicted freq. of heterozygous
individuals= .014…..1.4 %
q²= predicted freq. of homozygous recessive
individuals= .00005…..005%
• With a frequency of .005% (about 1 in 20,000), albinos are extremely rare.
• However, heterozygous carriers for this trait, with a predicted frequency of 1.4% (about 1 in 72), are far more
common than most people imagine.
• There are roughly 278 times more carriers than albinos.
• Clearly, though, the vast majority of humans (98.6%) probably are homozygous dominant and do not
have the albinism allele.
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the
percentage of the homozygous recessive genotype (aa) is 36%.
Using that 36%, calculate the following:
1. The frequency of the "aa" genotype.
2. The frequency of the "a" allele.
3. The frequency of the "A" allele.
4. The frequencies of the genotypes "AA" and "Aa."
5. The frequencies of the two possible phenotypes if "A" is completely
dominant over "a."
Find:
q²=
q=
p=
p²=
2pq=
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
aa= 36….. q²= .36
Now let’s input this information
Sq. Root of .36= .6
into the Hardy-Weinberg equation:
q = .6
p+q=1
_____ + .6= 1
p= .4
(p² + 2pq + q² = 1)
 Change to %s
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
Now let’s input this information
into the Hardy-Weinberg equation:
(p² + 2pq + q² = 1)
 Change to %s
p² + 2pq + q² = 1
(.4)² + 2(.4x.6) + (.6)² = 1
.16 +
.48 + .36 = 1
AA= 16%
Aa= 48%
aa= 36%
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
1. The frequency of the "aa" genotype.
36%
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
2. The frequency of the "a" allele.
.36 + . 24 (1/2 of 2pq)= .6 or 60%
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
3. The frequency of the "A" allele.
.16 + .24 (1/2 of 2pq) = .4 or 40%
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
4. The frequencies of the genotypes "AA" and "Aa”.
AA= 16%
Aa= 48%
The Hardy-Weinberg Principle Practice
• You have sampled a population in which you know that the percentage of
the homozygous recessive genotype (aa) is 36%. Using that 36%, calculate
the following:
5. The frequencies of the two possible phenotypes if "A" is completely dominant over
"a.“
48+ 16= 64% of the population will show the trait.
36% will be recessive for the trait.
The Hardy-Weinberg Principle Practice
• Please complete the Hardy-Weinberg practice problems (both sides)
The Hardy-Weinberg Principle Pre-Lab
• Solve.
• Fill out table
Find:
q²=
q=
p=
p²=
2pq=
Genotype Frequency of Gene frequency
allele pairs in (Freq. #/Total)
population
Homozygous
Dominant
Heterozygous
Homozygous
Recessive
Total
LL
Ll
ll
.25
p²
2pq
q²
The Hardy Har Har-Weinberg Principle Lab
• Read your Hardy-Weinberg Principle notes for background
• Write hypothesis. What do you think is going to happen to the allele
frequencies as we move from generation to generation?
P 1 (Parental Generation) P1
Homozygous
Dominant (LL)
8
Heterozygous
(Ll)
16
Homozygous
Recessive (ll)
8
Calculate gene frequencies for each.
.25
.50
.25
P 1 (Parental Generation) P2
Homozygous
Dominant (LL)
9
Heterozygous
(Ll)
18
Homozygous
Recessive (ll)
9
Calculate gene frequencies for each.
.25
.50
.25
F1 (Generation 1)
Homozygous
Dominant (LL)
Heterozygous
(Ll)
Calculate gene frequencies for each.
Homozygous
Recessive (ll)
F2 (Generation 2)
Homozygous
Dominant (LL)
Heterozygous
(Ll)
Calculate gene frequencies for each.
Homozygous
Recessive (ll)
F3 (Generation 3)
Homozygous
Dominant (LL)
Heterozygous
(Ll)
Calculate gene frequencies for each.
Homozygous
Recessive (ll)
F4 (Generation 4)
Homozygous
Dominant (LL)
Heterozygous
(Ll)
Calculate gene frequencies for each.
Homozygous
Recessive (ll)
F5 (Generation 5)
Homozygous
Dominant (LL)
Heterozygous
(Ll)
Calculate gene frequencies for each.
Homozygous
Recessive (ll)
The Hardy Har Har-Weinberg Principle Lab
• Please answer the 7 analysis questions on a separate piece of paper
• Staple to lab notes/data sheet
The Hardy-Weinberg Principle Lab Report
• Hypothesis
• Data collection
• 1-2 data tables
• Data Processing/Analysis
• 1-2 Graphs
• Conclusion
• Only part I