Genetics and DNA
The blueprint of life, written in a four-letter code that has been running for 3.8 billion years.
🔗 DNA Structure
DNA (deoxyribonucleic acid) is a double helix made of nucleotides. Each nucleotide contains a sugar, phosphate, and one of four bases: adenine (A), thymine (T), guanine (G), and cytosine (C). A pairs with T; G pairs with C. Watson and Crick described this structure in 1953.
📖 Genes and Proteins
A gene is a section of DNA that codes for a protein. The central dogma: DNA is transcribed into RNA, which is translated into protein. Humans have roughly 20,000-25,000 protein-coding genes, making up only about 1.5% of our total DNA.
🎲 Mendelian Inheritance
Gregor Mendel discovered that traits are passed as discrete units (genes). Dominant alleles mask recessive ones. A Punnett square predicts the probability of offspring traits. Blood type, eye color, and thousands of genetic conditions follow inheritance patterns.
🔧 Mutations
Changes in DNA sequence. Point mutations alter a single base. Insertions and deletions shift the reading frame. Mutations can be harmless, beneficial (driving evolution), or cause disease. Radiation (including nuclear) and certain chemicals are mutagens that increase mutation rate.
✂️ CRISPR-Cas9
A revolutionary gene-editing tool adapted from a bacterial immune system. A guide RNA directs the Cas9 enzyme to cut DNA at a specific location, allowing genes to be disabled or replaced. First used in humans in 2020 to treat sickle cell disease.
🗺️ The Human Genome
The complete human genome contains about 3.2 billion base pairs across 23 chromosome pairs. The Human Genome Project completed its first draft in 2003. A complete, gapless sequence was finally published in 2022 by the Telomere-to-Telomere consortium.