Hardy-Weinberg and Microevolution Flashcards
Exam 1
Population
A group of interbreeding individuals
-In the same area
-(Somewhat) isolated from other groups
-Tend to mate with those closer rather than farther away
*Can treat as separate groups with different gene pool
Populations differ…
Populations differ in genetic makeup
Gene pool
All alleles of all genes in a population
-Many genes have fixed alleles (homozygous)
-Some genes have two or more alleles
Genotypic Frequency
The percentage of each genotype in the population
-%AA, %Aa, %aa
Allelic Frequency
The percentage of each allele in the population
-%A and %a
Population #1: Three Phenotypes with 25 Total; 4 AA, 12 Aa, 9aa
4/25 = 16% = 0.16 AA
12/25 = 48% = 0.48 Aa
9/25 = 36% = 0.36 aa
These are genotypic frequencies
20/50 = 40% = 0.4A
30/50 = 60% = 0.6a
These are allelic frequencies
*Same allelic frequency as Population #2, but genotypic frequency is different
Population #2: Three Phenotypes with 25 Total; 7 AA, 6 Aa, 12 aa
28% AA
24% Aa
48% aa
These are genotypic frequencies
40% A
60% a
These are allelic frequencies
*Same allelic frequency as Population #1, but genotypic frequency is different
Population #3: Two phenotypes with 25 Total; 16 AA, 9 Aa
*aa never lives
64% AA
36% Aa
0% aa
These are genotypic frequencies
82% A
18% a
These are allelic frequencies
*Both allele frequency and genotypic frequency are different
*General appearance of the population is more green/yellow with no blue
Population #4: Four phenotypes with 25 total; 1 AA’, 14AA, 8 Aa, 2 aa
4% AA’
56% AA
32% Aa
8% aa
These are genotypic frequencies
74% A
24% a
2% A’
These are allelic frequencies
*Random mutation changes allele and genotype ratios and produces a new phenotype
*This gene now has 3 alleles in this population
Microevolution
Any change in population allelic or genotypic frequency over time
-Most fundamental unit of evolution
*Not random chance
Can we predict the genotypic and allelic frequencies in a population over successive generations?
Yes. If there is no selective pressure the frequencies should not change. If they do, it could be evidence that evolution is occurring
Hardy-Weinberg Principle has…
Hardy-Weinberg Principle has no microevolution
-Same frequency of alleles and genotypes in next generation
-The null hypothesis
Hardy-Weinberg Principle
States that given a set of assumptions, allele frequencies in a population will not change from generation to generation
Hardy-Weinberg Equilibrium Conditions
1) No mutations
2) Mating is random
3) No selection (offspring have equal survival
4) Population size is very large
5) No gene flow in or out
*The population is not changing
Hardy-Weinberg Equilibrium Example: A population of 500 flowers: 320 CrCr, 20 CwCw, 160 CrCw
64% CrCr
4% CwCw
32% CrCw
These are genotypic frequencies
80% Cr
20% Cw
These are allelic frequencies
*Each successive generation will have the same ratios
Hardy-Weinberg Equilibrium and Probability
If population has 80% (0.8) red alleles (Cr):
-The probability of one male or one female gamete with red allele = 80%
If mating is random with equal chance to produce offspring:
-Frequency of producing a particular genotype is the product of probabilities of each gamete
*Allelic frequencies are the same also
Developing the Hardy-Weinberg Equation
p = Frequency of dominant alleles
q = Frequency of recessive alleles
*Allelic frequency: p + q = 1
p^2 = Frequency of homozygous dominant genotypes
q^2 = Frequency of homozygous recessive genotypes
2pq = Frequency of heterozygous genotypes
*So in any generation
Genotypic frequency: p^2 + 2pq + q^2 = 1
Applying the Hardy-Weinberg Equation: In an isolated human population (assume H-W), the frequency of the Tay-Sach’s allele t is 0.02.
What is the chance that any one individual is a carrier?
Carriers are Tt
p(Tt) = % of heterozygotes = 2pq
q = 0.02
p + q = 1
p = 0.98
2pq = 2(0.98)(0.02) = 0.0392 or
3.92%
Applying the Hardy- Weinberg Equation: An island population of butterflies is in the H-W equilibrium. 64% have black stripes, a trait due to an autosomal dominant allele B.
What are the allele frequencies?
What % of the population is homozygous dominant?
What are the allele frequencies?
p^2 + 2pq + q^2 = 1
If 64% dominant phenotype, then 36% are homozygous recessive and q^2 = 0.36
q = \sqrt 0.36 = 0.6 = 60% b
p = 1-q = 0.4 = 40% B
What % of the population is homozygous dominant?
%BB = p^2 = (0.4)^2 = 0.16 = 16%
Using Hardy-Weinberg to Detect Microevolution
-Hardy-Weinberg is the null hypothesis
-If actual frequencies (ratios) differ from the expected (H-W) ratios, then the population is evolving
Using Hardy-Weinberg to Detect Microevolution: A population of 1000 ducks has: 500 AA, 200 Aa, 300 aa.
Is this population evolving?
Frequency a = (300x2 + 200) / 2000 = q = 0.4
p = 1- 0.4 = 0.6
Expected H-W ratios:
p^2 = (0.6)^ = 0.36 (360)
2pq = 2(0.6)(0.4) = 0.48 (480)
q^2 = (0.4) ^2 = 0.16 (160)
Actual (observed) ratios:
0.50 (500/1000)
0.20 (200/1000)
0.30 (300/1000)
The population is evolving
Using Hardy-Weinberg: In the Mushroom Kingdom, Yoshis come in 3 variants: red (RR), pink (Rr), and white (rr). Calculate the allele frequencies in a single Yoshi population where 75 out of every 1000 are white Yoshis, assuming the Yoshi population is in Hardy-Weinberg equilibrium.
p^2 + 2pq + q^2 = 1
75/1000 = 0.075
q^2 = \sqrt 0.075 = q = 0.27
1- q = p
1 - 0.27 = p = 0.73
R = 0.73 and r = 0.27
Using Hardy-Weinberg: Approximately how many of each Yoshi would you expect in the next generation that produces 2500 total individuals, provided they remain in the H-W equilibrium?
There was 75 white of original 1000 population
(75/1000)(2500) = 187 white
D) 1325 red; 975 pink; 187 white
