Biology

Genetics and molecular biology

DNA, transcription/translation, Mendel, meiosis.

Basics

DNA

A double helix with base pairs A–T and G–C. Replication is semiconservative. A gene is usually a DNA stretch that specifies a polypeptide or a functional RNA.

Central dogma

DNA → (transcription) RNA → (translation) protein. A codon of three bases codes one amino acid. Start: AUG (methionine). Stop: UAA, UAG, UGA.

Mendel

Segregation: alleles split in meiosis. Independent assortment: unlinked genes combine independently. A monohybrid heterozygous cross gives a 3:1 phenotypic ratio.

Mitosis and meiosis

Mitosis: diploid → diploid, growth and repair. Meiosis: diploid → haploid gametes, with crossing-over. Humans: 2n=46, gametes n=23.

Formulas

Hardy–Weinberg

p² + 2pq + q² = 1, p + q = 1

With random mating, infinite size, and no selection, mutation, or migration, allele frequencies stay put.

Symbols

p frequency of allele A
q frequency of allele a
2pq heterozygote frequency

Recombination and map distance

RF = recombinants / total, d(cM) ≈ RF × 100

Closer loci on a chromosome recombine less. Near 50%, they look unlinked.

Symbols

RF recombination fraction

Key table

Base pairs	A–T (2 H-bonds), G–C (3 H-bonds)
RNA	U instead of T; usually single-stranded; ribose
Human chromosomes	22 autosome pairs + XX or XY

In this field

The cell

Prokaryotes vs eukaryotes, organelles, membranes.

Metabolism

Photosynthesis, respiration, ATP, enzymes.

Evolution and ecology

Natural selection, phylogeny, trophic levels, cycles.

Human physiology basics

Homeostasis, circulation, nerves, immunity.

Plants and development

Plant tissues, hormones, developmental stages.

Immunity and microbes

Pathogens, innate and adaptive immunity, antibiotics and vaccines.

Nervous and endocrine systems

Neurons, synapses, hormones, and homeostasis — fast electrical and slower chemical signals.

Molecular lab sketch

Restriction enzymes, electrophoresis, PCR, and sequencing — a short principle sketch.

Population ecology

Exponential and logistic growth, carrying capacity, life history, predator–prey sketch.

Life’s diversity

Domains, a phylogeny sketch, homology versus analogy, and binomial names.

Biological macromolecules

Carbohydrates, lipids, proteins, and nucleic acids — structure and role sketches.