Preparatory Mindset
Think of the genome as the complete genetic BLUEPRINT. Understand how DNA is packaged into chromosomes (2 meters of DNA into a 5 micron nucleus), the cell cycle phases, and the critical difference between mitosis and meiosis.
Core Concepts
- Human genome: ~3 billion base pairs, 46 chromosomes (23 pairs) in somatic cells
- Somatic cells: Diploid (2n = 46); Gametes: Haploid (n = 23)
- DNA packaging: DNA → histones (nucleosomes) → chromatin → chromosomes
- Chromosome structure: Centromere (p = short arm, q = long arm), telomeres (end protection), kinetochore (spindle attachment)
- Karyotyping: Cells arrested at metaphase with colcemid → stained with Giemsa (G-banding)
- Base pairing: Guanine-Cytosine (3 H-bonds), Adenine-Thymine (2 H-bonds)
- Repetitive DNA: Centromeres, telomeres, Alu elements, LINE elements
- Cell cycle: Interphase (G1, S, G2) → Mitosis (M) → Cytokinesis
- Mitosis: 2n → 2n identical daughter cells (somatic cell division)
- Meiosis: 2n → 4 unique n gametes; crossing over at prophase I creates diversity
High-Yield Points
- Somatic cells: 46 chromosomes, gametes: 23
- G-C pairs have 3 H-bonds (stronger); A-T pairs have 2 H-bonds
- Meiosis produces genetic diversity (crossing over, independent assortment)
- Cells spend most of life in INTERPHASE, not mitosis
Topic Summary
The human genome is organized into 46 chromosomes. Mitosis produces identical cells for growth/repair; meiosis produces diverse gametes for reproduction.