Chromosomes and the near extinction of humankind

Sam Kean is up next with her new book on genetics and a blog on human genome. He will be explaining strange cancers, DNA palindromes and semordnilaps, interspecies hanky-panky, and the near extinction of humankind over the next few weeks.

Chromosomes are discrete bundles of DNA inside the cell nucleus, and they house our genes, named with size numbers. Chromosome 1 is the longest, chromosome 2 the second-longest, chromosome 3 (spoiler alert!) the third-longest, and so on. But Chromosome 21 is the odd one out! Because it's the 22nd-longest, and the shortest chromosome overall, roughly 3 million DNA bases shorter than chromosome 22.

On the other hand, Genes are units of inheritance that control body traits and get passed from generation to generation; they’re made of DNA, and cells “read” genes like blueprints to make things such as proteins. Each chromosome contains between a few hundred and a few thousand genes—scientists have had more latitude to indulge their creativity.

One of the most important genes in the entire animal repertoire—humans have a copy on Chromosome 7—and it’s crucial for embryonic development. Flaws in the gene lead to heart-breaking birth defects, and it’s no fun explaining to some poor mother that sonic hedgehog might kill her child.

This was only a starting introduction for you into the world of chromosomes and genes. More narrative stories about human history—tales many scientists assumed lost forever, are explained in the book The Violinist’s Thumb.