Population Genetics and Examination Preparation

Introduction to Practical Exam and Assignments

• The practical exam will be similar to the practice exam.
• Exam 4 grades are ready for return in class.
• Reflections can still be submitted for a score addition.
• Problem Set 3, due on the final day, will be handed out.
• Importance of course evaluations and the bonus for completion (80% required).

Final Exam Information

• Students can use a 3x5 inch note card on the final.
• Review session may be planned for further practice if desired by the class.

Population Genetics Overview (Chapter 26)

• Focus on population frequencies and how they change over time.
• Example question on determining frequency of homozygous recessive individuals:
• If 9 out of 100 individuals are homozygous recessive, frequency = 0.09.
• Working with allele frequencies is critical; e.g., if 200 copies of gene x exist, with 60 being recessive, frequency = 60 / 200 = 0.3.
• The Hardy-Weinberg equilibrium establishes that allele frequencies remain stable under certain conditions.

Hardy-Weinberg Principle

• Formula: p^2 + 2pq + q^2 = 1 and p + q = 1, where:
• p = frequency of dominant allele.
• q = frequency of recessive allele.
• p^2 = homozygous dominant frequency.
• q^2 = homozygous recessive frequency.
• 2pq = heterozygous frequency.
• Understanding how to apply these equations rather than memorize them is essential.

Example Problem

• Given: 500 plants, with 28 being homozygous recessive (dwarf plants).
• Calculate frequencies:
• f(q^2) = 28/500 = 0.056
• q = ext{ sqrt(0.056)} = 0.24
• p = 1 - q = 0.76
• p^2 and 2pq calculations followed by checking the total count to assure accuracy.

Evolution and Hardy-Weinberg Assumptions

• For a population to be in equilibrium, certain conditions must be met:
• No new mutations, no genetic drift, no gene flow, no natural selection, and random mating.
• If these conditions aren't met, the population may evolve, leading to changing frequencies of alleles.

Factors Causing Evolution

• Mutation:
• Acts as a source of genetic variation.
• Typically produces minor changes over many generations.
• Genetic Drift:
• Random changes in allele frequencies can lead to fixation or loss of alleles.
• Two important types:
  • Bottleneck Effect: Large population significantly reduced in size, leading to less genetic variability.
  • Founder Effect: A small group leaves a large population and starts a new population with lower variability.
  • Example: Cheetah population with low genetic variation due to past bottlenecks.
• Gene Flow:
• Migration can transfer alleles between populations, altering allele frequencies.
• Example problem calculating allele frequencies using migration data provided.

Future Topics

• Focus on natural selection and its various patterns, such as directional selection.
• Distribution of new problem set focusing on these topics.