Why was it so hard to decode the corn genome?

Question

My teachers growing up told me it was impossible to decode the maize genome. But yet its been done. Why was decoding the genome so significant, and what made it so difficult?

Answer 1

Hi there,

This is an old question, but I thought I would take a crack at it.

The corn genome is actually not overly complex or "difficult" for modern genome sequencing. The issue your teacher was referring to was probably to do with the DNA sequencing technology that was available at the time he/she said this (before 2009, when the corn genome was sequenced).

Before the early 2000s, the best sequencing method we had was called "Sanger" sequencing, which was slow and expensive. The first human genome was sequenced using this, and it took more than 10 years to do. In about 2005, new sequencing technology came along, called high-throughput or next generation sequencing. This technology was thousands of times cheaper than Sanger sequencing, and thousands of times faster. By the year 2015, it became possible to sequence a genome the size of the human one (a little bigger than the corn genome) in less than one day.

Although it's common to see plant genomes the size of the corn genome sequenced these days, the reality is that plant genomes are harder to sequence than animal genomes. This is because plant genomes have more "junk" or "repetitive" DNA. These are parts of the genome that do not contain any genes at all, but are full of long, repetitive segments of nucleotides (for example, AAAAAAAAAA or TTTTTTTTT). These segments are hard to decode, which means that special methods are often needed to figure out how such long repetitive stretches fit together. It's a bit like putting together a puzzle with near-identical pieces that are all the same color.

I hope this answers your question!

Dylan