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Except for certain moments - when cells are dividing, for instance - chromosomes don't form compact, countable bodies inside cells. Instead, they unravel and flop about, which makes counting chromosomes a bit like counting strands of ramen in a bowl.

From Sam Kean

Junk DNA - or, as scientists call it nowadays, noncoding DNA - remains a mystery: No one knows how much of it is essential for life.

From Sam Kean

Mutations can arise anywhere in the genome, in gene DNA and noncoding DNA alike. But mutations to genes have bigger consequences: They can disable proteins and kill a creature.

From Sam Kean

Geneticists in the early 1900s believed that nature - in an effort to avoid wasting precious space within chromosomes - would pack as many genes into each chromosome as possible.

From Sam Kean

Before the Human Genome Project, most scientists assumed, based on our complex brains and behaviors, that humans must have around 100,000 genes; some estimates went as high as 150,000.

From Sam Kean

Most mutations involve typos: Something bumps a cell's elbow as it's copying DNA, and the wrong letter appears in a triplet - CAG becomes CCG.

From Sam Kean

All human beings are, in fact, born with dozens of mutations their parents lacked, and a few of those mutations could well be lethal if we didn't have two copies of every gene, so one can pick up the slack if the other malfunctions.

From Sam Kean

Whereas recessive traits require two bad copies of a gene to become noticeable, a dominant trait expresses itself no matter what the other copy does. A benign example of dominance: If you inherit one gene for sticky wet earwax and one gene for dry earwax, the sticky earwax gene wins out every time.

From Sam Kean

The density of space junk peaks around 620 miles up, in the middle of so-called low-Earth orbit. That's bad, because many weather, scientific, and reconnaissance satellites circle in various low-Earth orbits.

From Sam Kean

No element gets people telling crazy stories like mercury does. People have told me tales about pharmacists waxing floors with mercury, mothers rubbing it into babies' skin to kill germs, and 10-year-olds coating dimes in it to make them shine, then blithely carrying them around in their pockets.

From Sam Kean

Sam Kean

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