Con Gen

Effective Population Size and Genetic Drift

• Contextual Introduction

  • Often discussed later in the material, but covered earlier due to relevance to recent paper.

  • Relationship to genetic drift emphasized.

  • Focus on effective population size ahead of the mutation topic and the selection discussion.

  • Anticipation of finishing material by Wednesday in preparation for the exam scheduled for next Monday (the 23rd).

  • Class reminder: No class on Friday.

• Assignment Timeline

  • Paper due next Friday; class prep altered due to presentation needs.

Definitions of Population Sizes

• Census Population Size

  • Defined as the total number of individuals in a population.

• Effective Population Size

  • Represents the number of individuals contributing to the next generation.

  • Unlike census size, accounts for factors like breeding capability and social hierarchy.

• Key Definitions and Identification

  • Importance of being able to not only identify but explain effective population size.

  • Link between idealized versus actual populations explained.

Assumptions of Effective Population Size

• Critical Assumptions

  • All adults can breed.

  • No generational overlap.

  • Constant number of breeding individuals.

  • No mutation or selection.

  • Random union of gametes.

• Application

  • Treats populations as a snapshot under various assumptions, providing nuanced insight about genetic diversity compared to census population size.

  • Effective population size can vary significantly from census numbers due to various factors.

Numerical Cases and Calculations

• Population Models

  • Example: A population of 1,000 individuals can have varying effective population sizes (e.g., 100 or 500).

  • Genetic diversity loss can mirror that of an idealized population under specific assumptions.

• Challenges of Calculation

  • Effective population size calculations are more complex than census figures, often requiring genetic information and accounting for additional factors.

NE to NC Ratio

• Meaning and Importance

  • Ratio of effective population size (NE) to census population size (NC) captures the relative health of genetic diversity in a population.

  • Typically, populations show a major gap where effective population sizes can be as low as 10% of census sizes, highlighting genetic risks.

Genetic Diversity and Hardy-Weinberg Equilibrium

• Equilibrium Assumptions Related

  • Reflect similar principles to those of Hardy-Weinberg equilibrium focusing on controlled systems.

• Concept Integration

  • Comparing actual populations’ dynamics to assumptions allows detailed insights into genetic diversity.

Mutations and Their Effects on Genetic Materials

• Nucleotides

  • Basic building blocks of nucleic acids consisting of nitrogenous bases (A, C, G, T), deoxyribose sugars, and phosphate groups.

  • Nucleosides are defined as nucleotides without nitrogen bases.

• Types of Mutations

  • Varieties exist, including silent mutations, point mutations, insertions, deletions, and frame shifts.

Different Types of Mutations

• Silent Mutations

  • Codon position unchanged.

  • Example: A change from cytosine to thymine may have no effect on the encoded amino acid.

  • Non-deleterious and adaptive traits often observed.

• Base Substitutions

  • Can be synonymous (no amino acid change) or nonsynonymous (result in a different amino acid).

• Example of Nonsynonymous Mutation

  • Sickle cell anemia linked to a substitution that causes a change in hemoglobin.

• Insertion and Deletion Impact

  • Changes in nucleotide sequence that can create frame shifts impacting overall protein synthesis.

Selection Mechanisms

• General Concept of Selection

  • Defined as specific traits becoming more common due to differential survival and reproduction.

  • Comparison with the phrase "survival of the fittest" redefined to focus on reproduction.

• Ernst Mayr’s Contributions

  • Discussed how the combination of chance (mutation) and