Behavioral Genetics and Animal Models

Behavioral Genetics

Animal Models

Codominance vs. Incomplete Dominance

• Codominance:

  • Defined as a genetic scenario where no allele can block or mask the expression of the other allele.

  • Both parental alleles are fully expressed in the phenotype.

• Incomplete Dominance:

  • Defined as a situation where the dominant allele does not completely mask the effects of a recessive allele.

  • Results in a blended intermediate phenotype.

• Key Differences:

  • Codominance features full expression of both alleles.

  • Incomplete dominance features a blend of phenotypes.

Important Terms

• Artificial Selection

• Inbred Strains

• Adoption Studies in Humans

• Cross-Fostering in Animals

Genetic Influences on Behavior

Specific Focus Areas

• Evidence from Artificial Selection:

  • Example: The domestication of dogs leads to noticeable genetic changes.

  • Refers to the neural crest hypothesis in developmental biology, showcasing how domesticated dogs differ from their wild counterparts.

• Causality Link Between Genes and Behavior:

  • Understanding the link between genetic traits and behavior.

  • Identification of genes and pathways associated with domestication syndrome.

Quantitative Genetics

• Definition:

  • Focuses on the genetics of complex traits which exhibit continuous variation.

• Key Questions:

  • Are genes involved in the trait?

  • How much influence do genes have?

• Examples of Continuous Traits:

  • Traits such as height and skin tone versus discrete traits like red or white.

Experimental Design in Quantitative Genetics

Types of Genetic Experiments

1. Selection Studies:

   • If a trait is heritable, selective breeding can enhance it (e.g., in dogs and lab mice).

2. Inbred Strain Studies:

   • Examining genetically influenced traits that manifest differences under the same environmental conditions.

   • Starting with diverse genetic backgrounds to breed traits like high or low sociability, producing homogenous and differentiated strains.

Selection Experiments in Dogs

• Dog Behavioral Traits:

  • Various traits selected for include:

  • Hunting abilities (e.g., retrieving on command)

  • Independent hunting from sight or scent

  • Guarding and fighting capabilities

  • Herding and assisting in vermin extermination

  • Social behavior traits clustered together.

Trait Clusters for Dog Temperament

Co-evolution of Dogs and Humans

• Historical Context:

  • Dogs diverged from grey wolves approximately 32,000 years ago.

  • Co-evolution driven by a shared environment influencing both canine and human developments over millennia.

• Evolutionary Changes Observed:

  • Significant parallels in brain and digestive system adaptations between domesticated dogs and humans.

Traits Selected During Domestication

• Desired Characteristics:

  • Increased sociability and obedience.

  • Reduction of survival instincts, allowing for greater tolerance of humans.

Domestication Syndrome Overview

• Significant Time Span:

  • 30,000 years later, features resulting from selection include behavioral adaptations:

  • Increased tameness and reduced fear responses.

  • Refined social interactions with humans.

Fox Domestication Experiment

• Generations:

  • Over 40 generations aimed to breed foxes that exhibit less biting behavior and increased friendliness towards humans.

• Tameness Scoring Method:

  • Pups evaluated at 7-8 months based on tameness expressed by engagement with humans:

  • Class III: Least domesticated

  • Class II: Allow petting; no friendliness shown

  • Class I: Friendly engagement with humans

  • Additional class (Class IE): Introduced for animals eager to interact with humans after six generations.

Tameness and Behavioral Traits in Domesticated Mammals

• Specific Traits Selected For:

  • Tameness is characterized by reduced aggression and increased docility.

  • Associated with diminished fight-or-flight responses.

• Brain Changes:

  • Documented reductions in brain size: 2% reduction in foxes, up to 35% in pigs, though mechanisms remain poorly understood.

Physiological Changes in Domesticated Species

• Identified Traits:

  • Depigmentation leading to white markings.

  • Alterations in skull structure (shorter snouts, smaller jaws).

  • Reduced tooth size and floppy ears.

• Genetic Considerations:

  • No single mutation is confirmed to replicate domestication effects; instead, influence is projected from a combination of point mutations and epimutation changes.

Neural Crest Cell Hypothesis

• Foundation of the Hypothesis:

  • Suggests domesticated species have lost some neural crest cells, affecting their development.

  • Important for cartilage formation and reducing cranial and bodily features.

• Origin of Neural Crest Cells:

  • Unique to vertebrates, deriving from embryonic ectoderm, integral to neural system development.

Embryological Origin of Neural Crest Cells

• Neural Development Process:

  • Involves neurulation: forming neural plates, grooves, and folds leading to the formation of the neural tube and crest.

• Implications for Domesticated Lineages:

  • Domesticated animals such as dogs may exhibit less neural tube formation adjustments compared to wild relatives.

Predictions of the Neural Crest Cell Hypothesis

• Emphasizes inherited behaviors' genetic underpinnings alongside the influence of selective breeding and its cascading effects.