Microevolution Overview

Inbreeding and Genetic Purging

• Continued discussion of microevolution focusing on inbreeding and its consequences.

• Habsburg Jaw: A notable deformity associated with the Habsburg dynasty from the 15th-17th century Europe, illustrating the effects of inbreeding.

Emerging Model Organisms

• Importance of Model Organisms: Major scientific advancements in the 20th century linked to model organisms like E. coli, yeast, Drosophila, C. elegans, Arabidopsis, and mice.

• Expansion of Models: Recent advancements in sequencing and functional genomics have led to the inclusion of less-studied organisms into research.

• Key Topics for Course:

  • Characteristics of model organisms

  • New technologies aiding emerging models

  • Lessons learned from emerging models in various fields: medicine, neurobiology, ecology, evolutionary biology, agriculture, and cell biology.

Textbook Reading Engagement Poll

• Request: Encouragement for students to engage in textbook readings, using the Slido app for results presentation.

Practice Exam Engagement Poll

• Request: Inquiry about completion of the practice exam, also using the Slido app for results presentation.

Lecture Outline Topics Overview

• Harmful mutations (deleterious recessives)

• Mutation-selection balance

• Genetic diseases

• Identity-by-descent

• Quantifying inbreeding

• Inbreeding depression

• Genetic purging

• Genetic rescue

Effective Population Size (Ne)

• Definition: Ne is the size of an idealized population that experiences the same rate of genetic drift as a real population.

• Key Influences:

  • Drift is affected more by effective size than total census population.

  • Only individuals contributing genetic information to the next generation count for Ne.

Characteristics of Ne

• Contrasts with Census Population: Ne is typically smaller than the census population.

• Factors Reducing Ne:

  • Consideration of breeding individuals only (not children or elderly).

  • Linkage of genes reducing genetic recombination decreases Ne.

  • Having more males in a population tends to lower Ne.

Cheetah Population Example

• Current Statistics: Approximate census population of cheetahs is ~7,100, reduced due to a bottleneck 10,000 years ago.

• Estimated Ne: 15.4.

Poll on Effective Population Size

• Poll Inquiry: Question posed about factors influencing effective population size, using Slido app for results.

Harmful Mutations Overview

• Mutation Impacts: Mutations can disrupt complex, evolved systems, mostly resulting in neutral or deleterious effects.

• Harmful Alleles: Most harmful alleles are recessive, as they can evade selection at low frequencies.

Mutation Frequency and Selection

• Mutation Introduction: Introduction of a new lethal recessive allele into a population, with initial homozygous frequency calculations.

Frequency Calculations

• Mathematical Representation:

  • The frequency of a lethal recessive allele (q) in a population can be calculated using Hardy-Weinberg equilibrium where p + q = 1, with p being the dominant allele frequency.

  • After a mutation introduces a new lethal recessive allele, the initial frequency of the recessive allele can be expressed as q = 1/(2N) in a small population, where N is the number of individuals.

  • The calculations will show how if there is a new mutation resulting in a lethal recessive allele, the calculation of frequency will show that initial homozygous frequency (homozygous recessive, or aa) in the initial population is given by q^2 = (1/(2N))^2, which illustrates the rarity of lethal recessives becoming homozygous.

Conclusion

• Understanding the mathematical underpinnings of allele frequencies helps in exploring the principles of microevolution, inbreeding, and the dynamics of genetic variation in populations.