Having tried my best at guessing what these terms mean, I now need to study what they actually do mean.

The thing is, I can’t just look them up and dump the definitions in my glossary. I have to understand them well enough to be able to explain them in simple terms. I have to really know what I am talking about.

I decided to dive into the middle and start with bicistronic genes.

The simplest definition I found so far is this one:

Having or involving two cistrons, loci responsible for generating a protein


So, yeah, it’s Wiktionary, not a holy, endorsed science textbook, but it’s a start, OK?

Here’s the challenge: I now need to understand what cistrons are. I know what loci means, sort of. It means ‘places’. But, having looked up loci, I see that it has quite a specific meaning in genetics.

Whew! We now have a rabbitholeful of terms to define, or an entire rabbit city, probably. So, let’s get started.

A now-disappeared reference somewhere in cyberspace tells me this:

Homologous chromosomes can have different alleles on them. Alleles are variants of the same gene that occur on the same place on a chromosome. (Through a mutation, they are different.) A locus refers to the location on the chromosome where the gene is found.

I understand well enough what a chromosome and an allele are, so for now I am not going to define these terms, although I realise that I will have to get back to them sooner or later to be sure.

Homologous chromosomes are chromosome pairs (one from each parent) that are similar in length, gene position, and centromere location. The position of the genes on each homologous chromosome is the same, however, the genes may contain different alleles.


I don’t remember for sure what a centromere is. I think it’s the bitty that joins two strands of something, but I am not going to look that up now either.

Let me sum up what I understand so far, drawing also from my past knowledge and combining it with what I now understand:

A person has several chromosome pairs. I don’t remember how many… twenty-six, I think. These pairs are called homologous chromosomes. Homo means ‘the same’. The chromosomes are the same in that they are libraries of instruction manuals (genes) for the same things. However, they may contain different versions (alleles) of these manuals. A locus is the or location where you can expect to find a particular instruction manual on the library shelf.

One thing that is new to me is that the genes may contain different alleles. I always thought that one says these are different alleles of the gene. So I will have to look that up to find out where I am making a mistake in my thinking, or whether my sources are wrong.

But let me get back to cistrons now. Cistrons are places on the chromosome shelf, and bicistronic means having two places responsible for encoding a (specific) protein… so wait, does this mean you need the books in both of those places to get the instructions for the protein, or does it mean you can find the same thing in two places?

I guess I will now have to find out what monocistronic means before I can continue. Other terms that have been trying to make eye contact with me in this context are vector and plasmid. I don’t think I will be able to avoid them much longer.

I’ll be back.