Fascinating series on Human Genome from Slate - a must read!!
I’m blogging about the human genome this month in conjunction with my new book on genetics, The Violinist’s Thumb. This series will cover strange cancers, DNA palindromes and semordnilaps, interspecies hanky-panky, and the near extinction of humankind. But I thought I’d start off with something basic—with names, the first step in getting to know somebody.
We’ll be getting to know each human chromosome and its personality over the next few weeks, as I’ll extract a story from one or two chromosomes for each post. Chromosomes are discrete bundles of DNA inside the cell nucleus, and they house our genes. But despite the importance of chromosomes to our basic essence—they’re one fundamental thing all humans share—geneticists sure didn’t expend much energy thinking up names for them. They were in fact named with all the creativity of shoe sizes. Chromosome 1 is the longest, chromosome 2 the second-longest, chromosome 3 (spoiler alert!) the third-longest, and so on.
The only break in the monotony comes with chromosome 21. You’d think this would be the 21st-longest, but no—it’s the 22nd-longest, and the shortest chromosome overall, roughly 3 million DNA bases shorter than chromosome 22. Back when scientists started cataloging human chromosomes, they had much poorer microscopes, and a difference of even many millions wasn’t easy to measure. That’s because chromosomes in living cells usually look like unraveled skeins of yarn, not the neat, plump, paper-doll pairs we’re used to seeing on karyotypes (like the snazzy one below). During this era, scientists mistakenly measured chromosome 21 as longer, and by the time they realized this, it had already become infamous as the cause of Down syndrome. (Down syndrome occurs when someone has three copies of chromosome 21 instead of the normal two.) Rather than risk confusion, scientists let the misnomer “21” stick.
I’m blogging about the human genome this month in conjunction with my new book on genetics, The Violinist’s Thumb. This series will cover strange cancers, DNA palindromes and semordnilaps, interspecies hanky-panky, and the near extinction of humankind. But I thought I’d start off with something basic—with names, the first step in getting to know somebody.
We’ll be getting to know each human chromosome and its personality over the next few weeks, as I’ll extract a story from one or two chromosomes for each post. Chromosomes are discrete bundles of DNA inside the cell nucleus, and they house our genes. But despite the importance of chromosomes to our basic essence—they’re one fundamental thing all humans share—geneticists sure didn’t expend much energy thinking up names for them. They were in fact named with all the creativity of shoe sizes. Chromosome 1 is the longest, chromosome 2 the second-longest, chromosome 3 (spoiler alert!) the third-longest, and so on.
The only break in the monotony comes with chromosome 21. You’d think this would be the 21st-longest, but no—it’s the 22nd-longest, and the shortest chromosome overall, roughly 3 million DNA bases shorter than chromosome 22. Back when scientists started cataloging human chromosomes, they had much poorer microscopes, and a difference of even many millions wasn’t easy to measure. That’s because chromosomes in living cells usually look like unraveled skeins of yarn, not the neat, plump, paper-doll pairs we’re used to seeing on karyotypes (like the snazzy one below). During this era, scientists mistakenly measured chromosome 21 as longer, and by the time they realized this, it had already become infamous as the cause of Down syndrome. (Down syndrome occurs when someone has three copies of chromosome 21 instead of the normal two.) Rather than risk confusion, scientists let the misnomer “21” stick.
No comments:
Post a Comment