gezzathorpe said:
I am having difficulty understanding your chart. I presume 'C' is carbs, but what is 'T', and why is your unit of measurement Kb (kilobytes)?
No C is the nucleotide Cytosine. The T stands for Thymine. The four nucleotides, guanine, adenine, thymine and cytosine are basic building blocks in DNA. You have 23 pairs of chromosomes and the sequence of nucleotides on one chromosomal strand are bonded to paired nucleotides on the other strand, rather like rungs on a ladder, except the two strands are twisted in a helix:
Cytosine is always paired with guanine and thyamine always paired with adenine. The C to T, or C => T transition is a copying error during replication. Where there should be a cytosine/guanine pairing or 'rung', there is a thyamine/adenine pairing. The 13910 Kb refers to the position of this mutant rung on the ladder. Starting at 0 with the bottom rung, you count 13,910,000 rungs up, and you're in the right area. If you have a look at this gene (AMY1), you'll see the nucleotides in sequence, 100 per line from 12851.8 Kb up to 12854.4 Kb
http://upload.wikimedia.org/wikipedia/c ... Y1gene.png
Looking at the map again
The red areas in northern europe indicate the frequency of the C => T transition at 13910 Kb, at 90% or above, the orange C => T between 80% and 90% and so on, decreasing in frequency as we go through the colour bands. As you say, most people in the UK can drink milk, although strictly speaking the C => T transition at 13910 Kb means that they produce the enzyme lactase which enables them to digest the carbohydrate lactose, the sugar found in milk. Most people in the world do not produce the enzyme lactase in adulthood. Production is normally switched off in the teens. A couple of other cultures also have mutations which allows lactase to be produced in adulthood, the cattle rearing Tutsi tribe of sub saharan Africa and the Bedouin pastoralists who traditionally drank camel's milk for example. There are 4 geographic areas where the population have high frequencies of what is known as a LP (Lactase Persistence) gene. Each however appears to have its own mutation which causes it. The general area on the chromosome which controls it is known as the MCM6 gene and the specific locations of the mutations which allow LP are -13910*C, -13,907*G, -13,915*G and -14,010*C. Any copying error at these loci, ie a T where a C should be or an A where a G should be and lactase production does not get switched off. There may be others of course, but we haven't found them. What is evident however is that the mutations are highly correlated with geographic regions. This is what we would expect as they are rare for a given location and are deemed to have happened only once, in one person, at some time in the past. The only reason why a gene propagates throughout a population in later generations, is because it conveys some sort of selective advantage.