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DNA, or deoxyribonucleic acid, is the genetic material housed within the nucleus of each human cell. It forms the structure of chromosomes and contains genes, which are short sequences encoding instructions for protein synthesis. Proteins perform essential biological functions including digestion, metabolism, immune response, muscle building, and growth. Understanding genetic material is foundational to the introduction to biological bases of psychology.

Humans typically have 46 chromosomes organized into 23 pairs within the cell nucleus. Each chromosome is a highly coiled structure made of DNA. These chromosomes carry genetic information inherited from both parents, with 22 pairs called autosomes governing physical traits and one pair of sex chromosomes determining biological sex.

Autosomes are 22 chromosome pairs that determine physical and biochemical traits such as eye color, blood type, height, and skin color. Sex chromosomes form the 23rd pair and determine biological sex. Females have two X chromosomes while males have one X and one Y chromosome, with the Y chromosome triggering male physiological development.

Genes are short DNA sequences that serve as fundamental units of heredity. They contain blueprints for synthesizing proteins, the building blocks of life that catalyze chemical reactions, provide structural components, and regulate cellular activity. Genes guide everything from cell division to enzyme and hormone synthesis, making them essential to biological processes.

Both males and females pass half of their chromosomes to offspring, including 22 autosomes and one sex chromosome, either X or Y. Half of an individual's genetic makeup comes from the mother's egg and half from the father's sperm, ensuring accurate transfer of genetic material to the next generation and creating unique genetic combinations.

The human genome includes all genetic material of an organism, functioning as an integrated system that dictates biological processes. It interacts with environmental factors, enabling organisms to adapt and evolve. This genetic coordination ensures each cellular function occurs precisely in response to internal and external stimuli, fundamental to survival, growth, and reproduction.

Genes encode instructions for synthesizing proteins that perform numerous essential functions. These proteins digest food, support cellular metabolism, fight infections, build muscle mass, and promote growth. Proteins also catalyze chemical reactions, provide structural components to cells and tissues, and regulate gene expression and cellular activity throughout the body.