Genetics
The science of genes and evolution in organisms.
DNA is the spiral molecular structure (double helix) made of 4 bases (A, T, G, C). These pair up: A <-> T, G <-> C forming a base 4 information system. Genes are segments of DNA that encode instructions for making proteins (or functional RNAs).
Polymerase Chain Reaction
PCR is one of the most important breakthroughs in the last century - allowing us to read DNA samples easily by exponentially copying specific DNA sequences, making millions of copies from a tiny sample.
How it works:
- Denaturation (~95°C) - Heat separates double-stranded DNA into single strands
- Annealing (~55-65°C) - Short DNA primers bind to target sequences
- Extension (~72°C) - DNA polymerase enzyme builds new complementary strands
This cycle repeats 25-35 times, exponentially copying the target DNA segment.
The DNA polymerase used in PCR comes from heat-loving bacteria that live in extreme environments. PCR was invented by Kary Mullis in 1983 (who had many LSD experiences).
CRISPR
CRISPR (Clustered Regularly Interspaced Short Palindromic Repeats) is a gene-editing tool that allows precise cutting and modification of DNA sequences.
How it works:
- Guide RNA - Designed to match the target DNA sequence
- Cas9 protein - Acts as molecular scissors, cutting DNA at the targeted location
- Cell repair - The cell's natural repair mechanisms fix the break, allowing deletion, correction or insertion of genes
Where it came from: Cas9 protein originates from bacterial immune system against viruses. Bacteria store viral DNA snippets in CRISPR arrays to "remember" past infections. When the virus returns, bacteria use this memory to cut and destroy viral DNA.
Common uses:
- Treating genetic diseases (sickle cell, some cancers)
- Agricultural improvements (drought-resistant crops)
- Research (studying gene function)
Why it's revolutionary:
- Earlier gene editing was slow, expensive, and imprecise
- CRISPR is fast, cheap (~$30/edit vs thousands), and highly accurate
- Democratized genetic engineering
Discovered by Jennifer Doudna and Emmanuelle Charpentier, who won the 2020 Nobel Prize in Chemistry.
Surprising Q&A
Does number of chromosome pairs correlate with complexity of an organism?
Chromosome number varies widely across species without correlation to complexity:
- Humans: 23 pairs
- Dogs: 39 pairs
- Fruit flies: 4 pairs
- Ferns: can have over 500 pairs
What matters for complexity of an organism is gene regulation, alternative splicing, non-coding RNAs and protein interactions - not just chromosome count or even total gene number.
What does it mean our DNA is 99% similar to chimps? how is DNA similarity computed?
- The 99% refers to aligned sequences (comparable regions)
- Doesn't account for insertions/deletions (indels) - chimps have different chromosome counts
- Non-coding regions can differ more than genes
- Overall genome similarity is closer to 96-98% when including structural differences
How was the tree of life calculated?
Key breakthrough: Carl Woese (1977) used ribosomal RNA sequences to reveal three domains of life (Bacteria, Archaea, Eukarya), revolutionizing classification that was previously based on visible features.
Modern approach:
- Sequences from multiple genes create more robust trees
- Whole genome comparisons for fine detail
- Molecular clocks estimate divergence times using mutation rates
Challenges:
- Horizontal gene transfer (especially in bacteria)
- Incomplete fossil record
- Convergent evolution (similar traits, different origins)
How many genes mutate in human sexual reproduction on average?
In human sexual reproduction, approximately 60-100 new mutations occur per offspring on average. These are de novo mutations—changes that appear in the child but weren't present in either parent's genome. Most occur during sperm production (~80% are paternal in origin and increase with age). Most mutations are in non-coding regions and have no effect.
Geographical Genetic Heritage
Why genetic heritage services like 23andme make no sense: They claim to analyse your genome and then send you a report of your ancestry, looking something like: 10% Norh-European, 20% Russian, 70% Chinese. These numbers make no sense since they are based on DNA samples from arbitrary reference populations in these regions but humanity has been travelling earth since its inception - so any regional reference sample is just a temporal snapshot at best. To claim you are X% from region Y is thus a misleading statement. One could only say with high uncertainty: you share X% of your DNA with most humans that lived in region Y Z years ago.
Genes and Intelligence
I have often witnessed people debating how much percent of intelligence of a human is genes vs (learning) environment - 50% / 50% or 30% / 70%? This is the wrong question to ask.
The intelligence of an individual is fundamentally limited by their DNA. The intelligence potential manifested in their genes is either unlocked by positive (learning) experiences or stays just a never reached potential.