Genetics and Evolution Notes

Page 1: Introduction

In this section, various key terms related to genetics and evolution are introduced. Each term is associated with a specific definition to aid understanding of concepts in population genetics and evolutionary biology.

Definitions

  • Mutation: The process that creates new alleles in a population.

  • Gene Flow: The movement of alleles within a population.

  • Migration: The movement of individuals in and out of a population.

  • Fitness: The probability of survival and reproduction in a particular environment.

  • Genetic Drift: A change in allele frequency in a population due to random sampling, often affecting small populations.

  • Natural Selection: A phenomenon where some organisms survive and reproduce better in certain environments than others.

  • Bottleneck Effect: A term used to describe what happens when a significant event reduces a large population to a much smaller size, impacting genetic diversity.

  • Founder Effect: Describes what occurs when a small population breaks off from a larger population and moves to a new environment, potentially having different allele frequencies.

  • Sexual Selection: Selection that amplifies differences between males and females.

Frog Population Study

Scientists studied Columbia spotted frogs in Montana and Idaho at different elevation breeding ponds to assess gene flow and genetic variation.

  • Environmental Differences: Frog survival and breeding can vary based on elevation, which may affect temperature, humidity, and food resources.

  • Findings:

  • Higher elevation ponds show decreased genetic variation, possibly due to a smaller base population and limited mating opportunities.

  • Lower elevation ponds experience higher gene flow, as frogs from distant ponds mate with one another, indicating better mobility and adaptability.

Page 2: Types of Natural Selection

In this section, students analyze different natural selection scenarios through graphical representations and explanations.

Types of Natural Selection

Directional Selection

Occurs when individuals at one end of the spectrum have higher fitness. Example: Tree frogs adapt to drying environments favoring traits that prevent skin dehydration during drought.

Stabilizing Selection

Favors intermediate phenotypes. Example: Body sizes of cichlids and kangaroos illustrate how certain sizes are favored due to ecological constraints like nesting areas or birth complications.

Disruptive Selection

Favors extreme phenotypes at both ends of the spectrum.Example: In a study of oysters, light and dark colors succeed while intermediate colors do not, indicating predator preference.

Page 3: Analyzing Genetic Changes

This page includes scenarios involving the bottleneck effect, founder effect, and gene flow, and how they affect the genetic composition of populations.

Scenarios

  1. Bottleneck Effect: Northern elephant seals reduced to 30 individuals, displaying minimal genetic diversity.

  2. Gene Flow: Blue jays randomly transporting acorns allow allele mixing across oak tree populations.

  3. Founder Effect: A group of beetles isolated post-volcanic eruption may diverge genetically from their original population.

  4. Impact of Catastrophe: Hurricane Hugo decimates the Puerto Rican parrot population, showcasing the bottleneck effect.

  5. Wildlife Crossings: Roads fragment wildlife populations, but crossings help reconnect bear populations, enhancing gene flow.

Page 4: Hardy-Weinberg Equilibrium Problems

This section emphasizes allele frequencies in a salamander population and applies calculations to determine genetic variation in a closed environment.

Population Genetics Calculations

  1. Calculate the fraction of homozygous recessive individuals:

  • q^2 = Solid Salamanders / Total Salamanders

  1. Calculate allele frequencies (q and p):

  • q = √(q^2); p = 1 - q

  1. Calculate fractions of homozygous dominant and heterozygous individuals:

  • p^2 = (p)^2; 2pq = 2(p)(q)

Evolutionary Implications

After introduction of a predator, assess population equilibrium and future predictions based on allele frequency changes. Consider factors affecting equilibrium such as selection pressures and mating patterns.

Page 5: Assessing Evolution and Hardy-Weinberg

This page examines another iguana population post-catastrophe, calculating allele frequencies and assessing evolutionary status.

Key Calculations

  1. Allele Count:

  • “A” alleles = 2(#large) + #medium

  • “a” alleles = 2(#small) + #medium

  1. Total Alleles and Frequencies:

  • Use total individuals to calculate total alleles and determine p and q.

  1. Equilibrium Status: Evaluate if the population remains in Hardy-Weinberg equilibrium post-catastrophe based on changes in allele distribution and possible selection pressures.

Prediction and Effects

After natural disasters, alleles' frequencies might shift dramatically affecting future generations; consider what effects may occur if there are subsequent changes or if conditions restore to previous states.