Study Notes on Genetics, Evolution, Development, and Plasticity 4.1

The assembly of the human nervous system is complex, similar to assembling items from a kit with ambiguous instructions, emphasizing the brain's plasticity.
- Plasticity: The ability of the brain to change in response to experience; it undergoes significant changes during early development and continues throughout life.

After studying this chapter, you should be able to:

Distinguish between genetic and epigenetic influences on development.
Describe the types of evidence researchers use to infer heritability.
Illustrate examples of evolutionary explanations in psychology.
Discuss the formation of new neurons in a mature brain.
Explain how axons seek specific targets.
Define apoptosis and the role of neurotrophins.
Cite examples of how experiences alter brain anatomy and function.
Discuss brain changes during adolescence and old age.
List mechanisms of recovery after brain damage.
Explain how remodeling in the cerebral cortex produces phantom limb experiences.

Behavior is influenced by both genes and environment.
- Facial Expressions: Studies show that even people born blind exhibit similar facial expressions to their sighted relatives, indicating genetic contribution.
Important issues arise in genetic vs environmental influences on traits, such as intelligence, sexual orientation, and weight gain.

Gregor Mendel's Work: Established that genes are the units of heredity that retain their identity across generations.
- Genes come in pairs; they are aligned along chromosomes, with the exception of male mammals having X and Y chromosomes.
Gene Definition: Classical definition denoted as sections of DNA that code for traits, now understood to be more complex with overlapping genes.

DNA: Deoxyribonucleic acid, the self-replicating material containing the genetic instructions.
RNA: Ribonucleic acid, a single-stranded molecule that serves as a template for protein synthesis.
- Composed of four bases: adenine (A), guanine (G), cytosine (C), thymine (T).
- mRNA (messenger RNA) helps create proteins by determining the sequence of amino acids.
- Example: Sequence of mRNA bases translates into amino acids, influencing protein structure and function.

Homozygous vs. Heterozygous:
- Homozygous: Two identical alleles (e.g., BB or bb).
- Heterozygous: Two different alleles (e.g., Bb).
Gene Dominance:
- Dominant: Expressed in homozygous or heterozygous conditions.
- Recessive: Expressed only in homozygous condition.

Brown eyes (dominant) vs blue eyes (recessive).
Tasting phenylthiocarbamide (PTC) sensitivity shows a dominant gene for high sensitivity.

Sex-Linked Genes: Influenced by sex chromosomes (X and Y).
- Red-green color vision deficiency is an example; more common in males due to having only one X chromosome.
Sex-Limited Genes: Present in both sexes but expressed predominantly in one due to hormonal regulation (e.g., breast size).

Mutation: Heritable changes in DNA structure, which can lead to altered protein functions.
- E.g., FOXP2 gene differences between humans and chimps relate to language development.
Microduplications and Microdeletions: Alterations affecting gene expression associated with conditions like schizophrenia.

Explains how experiences can change gene expression without altering the DNA sequence.
E.g., maternal nutrition during pregnancy can lead to later metabolic disorders.
Examples of epigenetic changes:
- Maternal care affects hippocampal gene expression, increasing vulnerability to stress.
- Memory formation alters gene activity in neurons, demonstrating the interplay of experience and genetics.
Histone Modification: Chemical groups (acetyl and methyl) can influence gene expression by loosening or tightening the DNA around histones.

Genetic influence is assessed by comparing monozygotic (identical) and dizygotic (fraternal) twins.
- Monozygotic twins share all genes, while dizygotic share half.
Adoptive Studies: Evaluating similarities between adopted children and their biological and adoptive parents assesses genetic vs environmental predilections.

Behaviors show varying heritability, with factors such as socio-cultural influences impacting characteristics like alcohol abuse or IQ.

Example: PKU (Phenylketonuria), a genetic disorder that can be controlled with a low-phenylalanine diet, illustrates that genetic predispositions can be altered through environmental interventions.

Genes affect behaviors through physiological mechanisms and indirect influences based on individuals' interactions with others.
Understanding heritability helps clarify the complexity and nuances of behavioral genetics.

Darwin’s Theory: Evolution is described as changes over generations concerning traits that confer reproductive advantages.
- Forces such as mutations contribute to variations among individuals that affect survival.

Lamarckian Evolution: The false belief in inheritance of acquired characteristics (e.g., the size of little toes).
Human Evolution: It did not cease due to modern advances, as evolutionary mechanisms continue through changes in reproduction.
Adaptation: Traits evolve for fitness concerning an environment but may not be beneficial in changed conditions.
Gene Benefit: Evolution operates on the gene level primarily, influencing individual fitness indirectly.

Human evolution led to larger brains due to dietary advantages and social collaboration.
Differences in gene expression critical for brain development make humans unique.

Discusses behavioral evolution and the natural selection process favoring genes that provided historical advantages.
Examples illustrate how traits in behavior may have evolved for survival (e.g., visual and feeding adaptations in various species).
Altruism: Examined from different perspectives, including kin selection (helping relatives) and reciprocal altruism (helping those who might help us).

Genes, though significant, do not solely dictate behavior—environment and experience play crucial roles.
Humans demonstrate the capacity for change and adaptation, underscoring the intricate relationship between genetics and behavior.