Here’s an organized summary and definitions for the key terms mentioned:

---

### Nature vs. Nurture

- Nature: Refers to genetic influences on development and behavior. Our inherited biological factors determine certain traits.

- Nurture: Refers to environmental influences, such as upbringing, culture, and life experiences, shaping development and behavior.

---

### Systems Theory

- Systems Theory: Emphasizes the interconnectedness of biological, social, and environmental factors in human development. It suggests that development occurs through interactions between systems (e.g., genetic, cellular, environmental), aligning with the bidirectional relationship between genetics and the environment.

---

### Genetics Fundamentals

- Human Genome: Composed of ~20,500 genes. Each gene is a segment of DNA on a chromosome.

- DNA Bases: Guanine, Adenine, Thymine, and Cytosine (G, A, T, C), whose order provides the genetic code.

- Chromosomes: Structures in the nucleus containing genes, inherited from both parents (23 pairs in humans).

- Alleles: Different forms of a gene. Homozygous alleles are identical, while heterozygous alleles are different.

---

### Genetic Expression

- Genetic Expression: The process where genetic information is used to produce proteins (not behaviors). Genes can be turned "on" or "off" by environmental factors, influencing biological functions.

- Regulatory Proteins: Act as switches for gene expression, determining whether a gene is active or inactive.

---

### Genotype vs. Phenotype

- Genotype: The genetic makeup of an individual, which remains static.

- Phenotype: The observable traits or behaviors, influenced by both genotype and environment.

- Plasticity: Refers to the adaptability of gene expression in response to environmental changes.

---

### Mendelian Genetics

- Dominant and Recessive Traits: Dominant traits appear with one dominant allele, while recessive traits require two recessive alleles.

- Mendelian Genetics: Explains simple inheritance patterns but is too simplistic for human behavior, which involves complex genetic interactions.

---

### Complex Genetic Effects

- Polygenic Inheritance: Multiple genes interact to produce a single trait or behavior (e.g., intelligence, personality).

- Pleiotropy: A single gene influences multiple traits or behaviors.

- Genetic Mutations: Changes in the DNA sequence that may be inherited or caused by environmental factors. Some mutations lead to disorders, while others (polymorphisms) allow for genetic diversity.

---

### Genetic Disorders

- Single Gene Disorders: Disorders caused by mutations in a single gene (e.g., PKU, cystic fibrosis).

- Chromosomal Disorders: Disorders due to abnormal chromosome numbers (e.g., Down syndrome caused by an extra chromosome 21).

- Interventions: Environmental modifications, gene therapy, and CRISPR (direct gene editing) are possible interventions.

---

### Behavioral Genetics

- Behavioral Genetics: Studies the relative influence of genetics and environment on behaviors. Methods include twin studies and adoption studies.

- Heritability: A statistic indicating the proportion of variability in a trait due to genetics (0 = all environment, 1 = all genetics).

---

### Gene-Environment Interactions

- Epigenetics: The study of how environmental factors affect gene expression without altering the DNA sequence (e.g., DNA methylation).

- Gene-Environment Correlations:

- Passive: Genetic predispositions create environments that support gene expression (e.g., a tall child is encouraged to play basketball).

- Evocative: Genetic traits evoke specific responses from the environment (e.g., a well-behaved child receives positive reinforcement).

- Active (Niche-Building): Individuals seek environments that match their genetic tendencies (e.g., risk-takers seek adventurous activities).

---

### Main Points

- Genes are static, but their expression is not. Environmental contexts influence which genes are expressed.

- The environment includes not just the physical world but also biological, social, political, and cultural influences.

- Development is driven by continuous bidirectional interactions between genetic and environmental factors.

---

This structure can guide your understanding of how genes and the environment shape development.