Assume that dark hair is dominant over light hair; if there are 5 students in a room of 20 students with light hair what can you tell me about the population of students using this equation:

p² + 2pq + q² = 1

Hardy WeinbergREVIEW

Evolution is simply a change in frequencies of alleles in the gene pool of a population over time.

• Genes determine most of an individual’s features, such as tooth shape or flower color.

• If an organism has a feature that is poorly adapted to its environment, the organism may be unable to survive and reproduce.

GENETICS AND EVOLUTION

Picture all of the alleles of a population as being together in a large pool called a gene pool.

The percentage of any specific allele in the gene pool is called

the allelic frequency.

What is the gene pool for this frog population???

What is the allelic frequency of green frogs? Red frogs?

Purple frogs?

Genetic Drift

• Genetic Drift – the random fluctuation in allele frequencies over time, due to chance occurrences alone

• It is more significant in smaller populations• It increases the chance of any given allele

becoming more or less prevalent when the number of individuals is small

Gene Flow

• Genes move with individuals when they move (emigrate or immigrate) into and out of a population…and it changes the gene pool

• Evolution occurs as a population’s genes and their frequencies change over time.•This can take millions of years for a species to change

GENETICS AND EVOLUTION

•A population in which the frequency of alleles remains the same over generations is in genetic equilibrium.

GENETICS AND EVOLUTION

• A population that is in genetic equilibrium is NOT evolving or changing.

According to Hardy-Weinberg, Evolution is …simply a change in frequencies of alleles in the gene pool of a population. 

• Alleles:

•Gene Pool:

• Population:

One of two or more forms of a gene that code for different versions of the same trait.

All possible genes and genetic combinations in a population.

A group of organisms from the same species and the geographic location.

Hardy-Weinberg came up with five basic reasons why a population would stay at genetic equilibrium:

3.  no mutations occur in any individuals DNA within this population.

Under these conditions it is obvious that evolution would NOT occur. 

There are no mechanisms of evolution acting on the population, so the process cannot happen--the gene

pool frequencies will remain unchanged.

5.  natural selection is not occurring

1.  the population is large, and genetic drift is not an issue (People won’t separate into cliques, and disease, predation, or any

other catastrophe will not occur).

4. all mating is totally random (No artificial selection or sexual selection)

2.  there is no gene flow, or migration in or out of the population

Hardy and Weinberg developed an equation we can use to calculate how

many individuals in a population are:

BB (Homozygous Dom.)

Bb (Heterozygous)

bb (Homozygous Rec.)

This is used to track allelic frequencies from generation to generation in a population

to monitor evolution OR changes in the gene pool.

This is the Hardy-Weinberg equilibrium equation.

p² + 2pq + q² = 1

p is defined as the frequency of the dominant allele

p = B

q is defined as the frequency of the recessive allele

q = b

Because there are only two alleles in this case, “B” and “b” the frequency of one plus

the other must equal 100%, so…

p + q = 1 (or 100%)

p² + 2pq + q² = 1

In this equation:

p² = homozygous dominant (BB) organisms in a population.

2pq = heterozygous (Bb) organisms

q² = homozygous recessive (bb) ones

p = B q = b

Albinism is a rare genetically inherited trait that is only expressed 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.

The Hardy-Weinberg equation (p² + 2pq + q² = 1), and 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 = .00005By taking the square root of both sides of this equation, we get:   

q = .007 (rounded)     

Knowing one of the two variables (q) in the Hardy-Weinberg equation, it is easy to solve for the other (p).

p = 1 – q

p = 1 - .007

p = .993

The frequency of the dominant, normal allele (A) is, therefore, .99293 or about 99 in 100.The next step is to plug the frequencies of p and q into the Hardy-Weinberg equation:

p² + 2pq + q² = 1(.993)² + 2 (.993)(.007) + (.007)² = 1

.986 + .014 + .00005 = 1This gives us the frequencies for each of the three genotypes for

this trait in the population:

p² = AA = .986 = 98.6%

2pq = Aa = .014 = 1.4%

q² = aa = .00005 = .005%

1. If 98 out of 200 individuals in a population express the recessive phenotype, what percent of the population are homozygous dominant?

Original problem source unknown

2. Brown hair (B) is dominant to blond hair (b). If there are 168 individuals with brown hair in a population of 200:

What is the predicted frequency of heterozygotes?A. 16% B. 40% C. 60% D. 48% E. 84%

Original problem source unknown

Brown hair (B) is dominant to blond hair (b). If there are 168 individuals with brown hair in a population of 200:

3. What is the predicted frequency of homozygous dominant genotype?

A. 16% B. 36% C. 60% D. 48% E. 84%

Original problem source unknown

4. What are the allele frequencies in an isolated field of 382 pink, 355 white, and 103 red

snapdragon plants?

Original problem source unknown

5. A population of turtles (in Hardy Weinberg equilibrium) is variable for the length of their tail. Long tails are dominant to short tails. 25 have long tails and 75 have short tails. If 400 baby turtles are born in the population, predict how many of the offspring will have long tails and how will have short tails.

Original problem source unknown

6. A population of 1000 individuals has 49 people that are left-handed. Assume left-handedness is homozygous recessive and that this population is in Hardy Weinberg equilibrium. Calculate p and q. What is the frequency of homozygous

dominants, heterozygotes, and homozygous recessives? How many individuals in the population carry the allele for left-

handedness, but are not left-handed?

Original problem source unknown

7. Assume 1 in 10,000 babies born in the US have PKU (which is recessive). What is the frequency of carriers for this allele?

8. 30,000 individuals in the United States have cystic fibrosis. Assuming the population is in Hardy Weinberg equilibrium how many individuals are carrier of the disease? Assume the US population is 316,000,000.

Bell Ringer

• In your journal...