Creationists And Missing Chromosomes

I have little respect for creationism as an intellectual pursuit (although I do know some creationists that have my utmost respect as people). Often though, we see a particularly nasty kind who are homophobic and boast of their ignorance, so I thought I would mix some science with taking the piss out of creationists here.

Our DNA is neatly packaged into structures called chromosomes. These are basically protein cores around which the DNA is wound. A DNA molecule can be seen here winding around proteins to form beads (nucleosomes) which are then further coiled into higher order structures. The video ends showing a cell dividing. Other proteins can then bind to these structures. The protein components of the chromosome helps regulate gene activity (expression), DNA replication and makes sure daughter cells get the correct number of chromosomes when a cell divides; or helps halve the number of chromosomes when we make eggs or sperm. Sperm cells have the smallest nucleus of all human cells and are therefore particularly good packagers of DNA.

The basic anatomy of a chromosome is rather simple. It consists of a centromere and telomeres at either end (Figure 1). The centromere is crucial in organising cell division and the telomeres stabilise the ends of the chromosome. Telomeres are made of short (usually 6) nucleotide repeats. In humans, the sequence is TTAGGG. This can be repeated over 50 times at each end of the chromosome. Interestingly, some internal chromosome structures can also be seen by staining them. Each chromosome also has its own specific pattern of bands (Figure 2).

Figure 1: chromosome structure.

Figure 2: banding in human chromosomes (arranged in pairs)

So, now to the point. Chimps have 24 pairs of chromosomes and we only have 23 pairs. This provides a potential challenge to evolution. At this point if you are a fundie, you will probably shout “Hallelujah”, dance about naked with a communion chalice on your head and claim the magic sky daddy did it. Genesis don’t talk about no evilution, so it is the work of the Devil and that's all you need to know. You then head off to your KKK meeting and claim that black men were created different for a reason before being put in jail for tax evasion – still, you can always buy some drugs off Ted Haggard – who is completely heterosexual – allegedly (wouldn’t mind so much if he kept his vitriol to himself).

If however, you wish to look beneath the surface, we can actually test evolution. Two main possibilities occur to a non creotard. The first is that a chromosome from a common ancestor with chimps split in two, this is unlikely as all chimp chromosomes have a telomere. We shall see more evidence against this hypothesis soon.
The second possibility is that two ancestral chromosomes fused after we diverged from our common ancestor with chimps. There are several predictions that can be made and tested – any one could potentially prove evolution false.

1. We should be able to align chromosome banding patterns between two chimp chromosomes and a human one if fusion has occurred. This is the case. It is Human chromosome two that lines up with two chimp chromosomes that are now called chimp 2a and 2b (Figure 3).

Figure 3: alingnment of human and chimp banding patterns

2. We should find telomere sequences inside the chromosome if a fusion has occurred. This is also what we find (figure 1). In fact, they start to reverse suggesting the ancestral chromosomes fused head to head or tail to tail. We can even tell where the fusion took place to with in 15 nucleotides. It occurred between nucleotides 114 455 823 and114 455 838.

3. Genes should appear in the same order above and below the fusion. I took a gene at random from above the fusion (RasGRP2) and one below the fusion (HOXD8). Lets see how the gene order compares:

Human chromosome 2: CARD12, TTC27, LTB1, RasGRP3, CRIM1

Chimp chromosome 2a: CARD12, TTC27, LTB1, RasGRP3, CRIM1

Human chromosome 2: PDK1, CCA7, CHN1, HOXD8, HOXD4

Chimp chromosome 2b: PDK1, CCA7, CHN1, HOXD8, HOXD4

Looks like they are in the same order to me – what do you say Mr fundie? What’s that? God did it that way to look like evolution to test our faith? My, you must feel special that god does not ask you to think.

4. We should see evidence of two centromeres. Guess what, that’s right, we do. The functional one lines up with one of the chimp ones, and the other one is still identifiable but non functioning. It also is in the same corresponding position as the other chimp one.

That's mankind's missing chromosome sorted. Now we just need to find out what happend to the ones that creotards are lacking.