Genotype, Phenotype & Development

• Three key elements of the model of interaction:

Genotype

• The genetic material inherited by an individual

Phenotype

• The observable expression of that genotype
• Includes body characteristics and behavior

Environment

• Everything surrounding the individual excluding genes

• Genes produce proteins and start/stop protein prodution of other genes, known as regulatory genes

• There are over 5,000 known human diseases and disorders due to genetic origins

• Recessive genes associated with PKU, sickle-cell anemia, cystic fibrosis

• A single dominant gene is related to Huntington's disease

• Sex-linked inheritance is related conditions of Fragile-X syndrome and hemophilia

• Neurodivergent phenotypes have a genetic basis, but the specific genetic mechanism is not established such ADHD, Bipolar disorder, Tourette's Syndrome, and Autism

• To understand what genes and proteins contribute to behavioral development, it is important to specify how the genes link to behavior

• Genes link to proteins, but then need to understand how proteins link to behavior

• One clear instance of how genes link to behavior is found in genes linked to behavioral development across differing levels

CF-Gene Example

• Underproduction of protein leads to an organ effect of build up of mucus in the lungs, leading to sickness/disease
• Other examples attempt to link genes and behavior

Novelty Seeking Example

• A novelty seeking gene will lead to a build-up of dopamine receptors, which can cause excitability in the cortical areas, leads to thrill seeking or "approach" behaviors.

Disrupted Aggression Gene Example

• A disrupted aggression gene causes a failure to produce nitric oxide (neurotransmitter) that leads to a failure to inhibit brain areas involved in aggression, this can lead to aggressive behaviors
• Most of these conditions are often polygenic
• Challenges remain in linking genes and behavior

Important Aspects of Genes and Proteins

• Clearly tied to some diseases
• Clearly part of the basic machinery of life
• Need a better understanding about the "levels" between genes and behavior and their interaction
• The explanations of how gene-protein-organ-behavior links play out over developmental time are needed

Behavior Genetics

• How variation in behavior and development results from gene and environment interactions.
• Most traits of interest include multiple factors

Behavior Genetic Studies

• Trait should be measured in people who vary genetic relatedness
• Look for higher correlations measures of traits for individuals who are genetically more similar and those who share the same environments

Twin Studies

• Correlations found on a trait of interest
• Compare monozygotic vs. dizygotic twins

Adoption Studies

• Determines whether adopted children are more like their biological relatives, or more like there adopted relatives

Heritability

• A statistical estimate of the proportion of the measured variance on a given trait among individuals given population that is attributable to the genetic differences among those individuals

Shared vs. Nonshared Factors

• Shared environment is growing up together in the same family
• Nonshared environment includes experiences unique to the individual

Nervous System, Brain and Behavior

Stages of Neural Development

• Cell production (proliferation)
• Cell migration
• Cell differentiation
• Synapse formation (synaptogenesis)
• Cell death
• Synapse rearrangement (synaptic pruning)

Neural Development - Cell Migration

• Spatial Layering where new cells push old cells out, or new cells migrate to the outside
• Chemical signals help to guide migration
• Glial rail, where cells ride glial fibers to migrate

Neural Development - Cell Differentiation

• Depends on parent cells, location and chemical signals

Neural Development - Synapse Formation

• Cells elongate at their axons to form connections (synapses) with other cells
• Each cell may form multiple synapses

Neural Development - Cell Death

• May be a result of cell overproduction
• Cells that don't receive nutrients may die
• Inactive cells may die

Neural Development - Synapse Rearrangement

• Post cell death - remaining cells make new synapses
• Synapses that are inactive will be pruned - or lost

Higher Brain Functions

• Frontal lobe is involved in executive functions.
• Parietal lobes in spatial processing.
• Temporal lobes in memory.
• Occipital lobes in visual processing.
• Primary motor cortex controls voluntary movements.
• Primary somatosensory cortex processes tactile information.
• Primary visual cortex processes visual information.
• Primary auditory cortex processes auditory information.
• Primary olfactory cortex processes olfactory information.
• Cortices/lobes have different functions, but are interconnected

Neural Development and Behavior

• Changes in the 6 stages of neural development provide global constraints on how experience can shape the brain
• Changes can be observed in changes in grey matter= the 'working' tissue in cortex
• Early over production of connections, followed by pruning later on in development

Experience and the Brain

• The brain shows amazing plasticity or flexibility even with global constraints
• Experience-expectant plasticity and experience-dependent plasticity

Experience-Expectant Plasticity

• The process through which the normal wiring of the brain occurs in part as a result of the general experiences.

A Key Component is Vulnerability

• Vulnerability means if the expected experience is not available, development will be impaired.
• Sensitive periods of timing are key
• Specific examples are found the somatosensory cortex
• Results suggest experience-dependent competition and selection

Experience-Dependent Plasticity

• Neurons are very flexible
• The left hemisphere is active for language, the right hemisphere can be active for language if the left hemisphere is damaged in childhood
• Experience matters in neural development

Brain Plasticity

• Allows potential for recovery after brain damange
• Recovery depends on the extent of the damage, as well as which aspect of that brain is developing at the time of damage
• Bad timing for brain damage is during prenatal development during neurogenesis and neural migration
• Decent timing for brain damage is during infancy/early childhood synaptogensis and pruning