Evolution 7 - Hardy-Weinberg Principle

Question 1

What are the 5 agents of evolutionary change?

Answer 1

-Mutation
-Gene Flow
-Non-Random Mating
-Genetic Drift
-Selection

Question 2

What is a population?

Answer 2

A population is a localized group of interbreeding individuals.

Question 3

What is a gene pool?

Answer 3

A gene pool is a collection of alleles in a particular population.

Question 4

What is the difference between alleles and genes?

Answer 4

• Genes are DNA sections that code for specific proteins or functional RNA, which play a crucial part in biological functions.
• Alleles, however, are variations of these genes, leading to diverse traits such as eye or hair color.

Question 5

What is allele frequency?

Answer 5

How common that allele is in the population (how many of A or a in whole population).

Question 6

What does it mean when a population evolves?

Answer 6

• Evolution is a change in allele frequencies in a population.

Question 7

What conditions would cause allele frequencies not to change? (1 point, 5 subpoints)

Answer 7

• In a non-evolving population, you would need to remove all agents of evolutionary change.
  1. Very large population size (No genetic drift)
  2. No migration (No gene flow in or out)
  3. No mutation (No genetic change)
  4. Random mating (No sexual selection)
  5. No natural selection (Everyone is equally fit)

Question 8

In a non-evolving population, what are preserved? (2 points with 2 subpoints)

Answer 8

-Allele frequencies are preserved, and they are said to be in Hardy-Weinberg equilibrium.
-But:
1. Natural populations are rarely in Hardy-Weinberg equilibrium.
2. However it provides a useful model to measure if evolutionary forces are acting on a population.

Question 9

How do you count Alleles? (Hardy-Weinberg Theory)

Answer 9

• Assume 2 alleles = B, b
• Frequency of dominant allele (B) = p
• Frequency of recessive allele (b) = q
• Frequencies must add up to 1 (100%), so:
  p + q = 1

Question 10

How do you count Genotypes? (Hardy-Weinberg Theory)

Answer 10

-Frequency of homozygous dominant: p x p = p^2
-Frequency of homozygous recessive: q x q = q^2
-Frequency of heterozygotes: (p x q) + (q x p) = 2pq
-Frequencies of all individuals must add to 1 (100%), so:
p^2 + 2pq + q^2 = 1

Question 11

What are the Hardy-Weinberg formulas?

Answer 11

-Alleles (B and b): p + q = 1
-Genotypes (BB, Bb, and bb): p^2 + 2pq + q^2 = 1

Question 12

In the part of the formula, (p+q)^2, where can I find information about the frequency of allele types?

Answer 12

p = Frequency of allele B
q = Frequency of allele b

Question 13

In the part of the formula, p^2 + 2pq + q^2, where can I find information about the frequency of allele combinations?

Answer 13

-p^2 = Frequency of BB (homozygous dominant)
-2pq = Frequency of Bb (heterozygous)
-q^2 = Frequency of bb (homozygous recessive)

Question 14

What is the part of the formula that tells us the frequency of the allele combination BB in a population?

Answer 14

p^2

Question 15

What is the part of the formula that tells us the frequency of the allele combination Bb in a population?

Answer 15

Add “Bb” and “Bb” together to get 2pq

Question 16

What is the part of the formula that tells us the frequency of the allele combination bb in a population?

Answer 16

q^2

Question 17

What are the steps to solving Hardy-Weinberg problems?

Answer 17

• Remember to use proportions in your calculations, not percentages!
  1. Examine question to determine what information is given; In most cases this is the frequency of the homozygous recessive phenotype q^2 or the allele q.
  2. Take the square root of q^2 to find q or multiply q to find q^2
  3. Find p by subtracting q from 1 (p = 1 – q)
  4. Find p^2 by multiplying it by itself (p2^2= p x p)
  5. Find 2pq by multiplying p x q x 2
  6. Check that your calculations are correct by adding values for p^2 + q^2 + 2pq

Question 18

What does the Hardy Weinberg principle show?

Answer 18

It shows that In a non-evolving population, allele frequencies are preserved (they are said to be in Hardy-Weinberg equilibrium).

Question 19

Why do we use the Hardy Weinberg principle?

Answer 19

We use it to measure if evolutionary forces are acting on a population.

Question 20

What are the criteria that must be met? (5 points)

Answer 20

• Very large population size (no genetic drift)
• No migration (no gene flow in or out)
• No mutation (no genetic change)
• Random mating (no sexual selection)
• No natural selection (everyone is equally fit)

Question 21

A population of mice has a gene consisting of 90% B alleles (black fur) and 10% b alleles (gray fur). Determine the proportion of offspring that will be black and the proportion that will be gray.

Answer 21

Recessive allele q = 0.1 Given
Dominant allele p = 0.9 1 – q = p 1 – 0.1 = 0.9
Recessive phenotype q2 = 0.01 q x q = q2 0.1 x 0.1 = 0.01
Homozygous dominant p2 = 0.81 p x p = p2 0.9 x 0.9 = 0.81
Heterozygous 2pq = 0.18 2 x p x q = 2pq 2 x 0.9 x 0.1 = 0.18
Check q2 + p2 + 2pq = 1 0.01 + 0.81 + 0.18 = 1
Black: 0.99
0.81 + 0.18 = 0.99
Gray: 0.01

Question 22

A population of 134 lizards has 81 individuals with green skin and a gg genotype. The remaining 53 individuals have yellow skin and therefore have either the GG or Gg genotype. What proportion of the population are homozygous dominant?

Answer 22

Recessive allele q = 0.77 √0.60 = 0.77
Dominant allele p = 0.23 1 - 0.77 = 0.23
Recessive phenotype q2 = 0.60 81/134 = 0.60
Homozygous dominant p2 = 0.05 0.23 x 0.23 = 0.05
Heterozygous 2pq = 0.35 2 x 0.77 x 0.23 = 0.35
0.60 + 0.05 + 0.35 = 1