1. Evolutionary Change in Populations
Chapter 18

2. Frequencies Gene pool – all the alleles in a population
Genotype frequency – total = 1.0 (100%)
homozygous dominant
heterozygous
homozygous recessive
Phenotype frequency – total – 1.0 (100%)
dominant
Recessive
Allele frequency
A or a
Each individual has 2: AA, Aa, or aa

3. Hardy-Weinberg Principle
A way of measuring if a population is evolving
Non-evolving populations ‘fit’ the principle – they are in genetic equilibrium
Five conditions must be met:
random mating
no net mutations
large population size
no migration
no natural selection
In other words: no evolutionary change

4. Hardy-Weinberg Principle…
Shows that the process of inheritance by itself does not cause changes in allele frequencies
Explains why dominant alleles are not necessarily more common than recessive ones
Seldom occurs in the natural world but instead provides us with a model for understanding evolution in sexually reproducing populations

5. Hardy-Weinberg Principle…
p = frequency of dominant allele
q = frequency of recessive allele
Therefore:
p + q = 1
From this we know that:
p = 1 – q (frequency of dominant allele)
q = 1 – p (frequency of recessive allele)

6. Hardy-Weinberg Principle…
Each individual has 2 alleles, therefore:
p pq + q 2 = 1
{AA + 2Aa + aa = 1} remember, there are 2 different ways an individual can inherit Aa
What the heck does this mean??

7. Problem #1
You have sampled a population in which you know that the percentage of the homozygous recessive genotype (aa) is 36%. Using that, calculate the following:
The frequency of the aa genotype
The frequency of the a allele
The frequency of the A allele
The frequencies of the genotypes of AA and Aa
The frequencies of the two possible phenotypes if A is completely dominant over a

8. Problem #2
Sickle-cell anemia is an interesting genetic disease. Normal homozygous individuals (SS) are more susceptible to malarial infection. Those with the sickle-cell trait (ss) often die due to the condition. Heterozygous individuals (Ss) tend to survive better than either of the homozygous conditions. If 9% of an African population is born with a severe form of sickle-cell anemia (ss), what percentage of the population will be more resistant to malaria because they are heterozygous (Ss) for the sickle-cell gene?

9. Problem #3
There are 100 students in a class. Ninety-six did well in the course whereas four blew it totally and received a grade of F. In the highly unlikely event that these traits are genetic rather than environmental, if these traits involve dominant and recessive alleles, and if the 4% represent the frequency of the homozygous recessive condition, calculate the following:
The frequency of the recessive allele
The frequency of the dominant allele
The frequency of heterozygous individuals

10. Problem #4
Within a population of butterflies, the color brown (B) is dominant over the color white. And 40% of the butterflies are white. Given this simple information, calculate the following:
The percentage of butterflies in the population that are heterozygous
The frequency of homozygous dominant individuals

11. Problem #5
A rather large population of Biology instructors have 396 red-sided individuals and 557 tan-sided individuals. Assume that red is totally recessive. Calculate the following:
The allele frequencies of each allele
The expected genotype frequencies
The number of heterozygous individuals that you would predict in this population
The expected phenotype frequencies
Conditions happen to be really good this year for breeding and next year there are 1,245 young Biology instructors. Assuming all of the H-W conditions are met, how many of these would you expect to be red-sided and how many tan-sided?