In the previous course, we also covered genome mapping in which we were analyzing patterns of inheritance
by checking out the crossing over frequencies between certain genes that are phenotypically expressed.
We can look at those recombination frequencies to estimate the distances, say, between A and B
and between B and C. Then we could do a three-point cross where we estimated them between A and C.
This was purely by looking at the progeny, the offspring involved in crosses and gave us a relative distance.
Now, we have more sophisticated mapping techniques because of DNA sequencing. But before, we used to place
these genes relative to each other using cytologic maps, using banding patterns and landmarks within DNA
to stack pieces up and to see where they belonged. We used sequence tag sites from one segment of DNA
to another segment of DNA. Those tag sites help us line up those pieces. So, you should recall all of that information.
Now again, we have the more sophisticated techniques. You’ll see first our Sanger dideoxy. This figure should look
very familiar. Then we talked about clone-by-clone sequencing. So, we’re still using this Sanger sequencing
but we’re cutting up the genome into thousands of pieces, millions of pieces, maybe even more. We’re lining them up
using computer analytics. Then shotgun was more of chopping the whole genome rather than chopping it in pieces
and then smaller pieces, really just shot gunning it and chopping the genome randomly into thousands and thousands,
millions of pieces and then using more sophisticated computer techniques to add up all those pieces and give us
the whole genome sequence. So, the technique of sequencing and genome mapping is becoming less and less
expensive. It started out being super expensive like billions of dollars just for one individual. Now, it’s coming down
in the neighborhood of $1000 per individual. So with this technology, we really are opening up the forefront
of genetics. In the name of genomics, the things that we’ve covered previously are first of all, looking through
the genome to establish, start, and stop codons and where the various genes are. But then we had the question of
what are those genes and in which cells are they actually expressed. So, expressed sequence tags or ESTs
are something we used to see which parts of the genome are actually expressed versus which parts are actual genes
that are not being expressed. So, when we look for expressed sequence tags in a cell, we can tell that that gene
is being expressed. Then we looked at microarrays or using microchips, biochips, whatever you want to call them
in order to line up all of the pieces and tell us when they are being expressed. So first of all, is this a gene?
Does it have a start or stop codon. Then we looked at telling if it’s expressed in that particular cell. For example,
we don’t need our eye color expressed in our hair. Then the key is when is it expressed so that we can make
much more detailed analysis of someone’s genetic makeup and how that might be associated with disease.