Wednesday, December 5, 2007

A Response to Pharyngula: Human Chromosome 2 and Balanced Translocations

Pharyngula's Blog in response to Casey Luskin

Balanced translocations in humans result in 45 chromosomes, horrendedous mutations, or nothing at all.

See here for a helpful diagram (source - Newcastle upon Tyne Hospitals):

In other words you can have these scenarios:

1. The exact same genome from before (ie that it has 46 chromosomes)
2. 45 Chromosome (the balanced translocation is passed on)
3. Monosomy- 45 chromosomes and almost invariably harmful
4. Trisomy - 46 alleles, but with an extra chromosome - almost invariably harmful

Evolutionists are purposing that our "common" ancestor had 48 chromosomes evidenced by our chromosome 2 that looks like 2 primate chromosomes fused.

So here's the scenario.

1. Balanced translocation (BT1) - 47 chromosome
2. Mated and passed on (BT1).
3. BT1 confers some selective advantage, though it is the same genetic material, and 3/4 of its offspring would not transfer BT1 and 1/2 have severe anamolies.
4. Another balanced translocation happens (BT2)
5. Progeny of BT1 and BT 2 transfer their respected balanced translocations (25% chance that the progeny receive BT1 and BT2).
6. The coveted 46 chromosome progeny!
7. Unfortunately there are no other 46 progeny to copulate with unless it is his sister.
8. What about their progeny?!?! It is well known that consanguineous (genetically related) offspring have severe problems as well.

Of course there are lots of other things to this such as certain chromosomes are more likely to translocate than others (in humans 13, 14, 15, 21, and 22) - what chromosomes are more likely to translocate in modern primates, the ones that are similar to our chromosome 2?

Or the fact that this would have needed to happen in a significantly short time (see my post on Haldane's dilemma) with the BT1 progeny population growing sufficient enough to create enough random events for the BT2 translocation. In fact, they would need a lot more progeny b/c 3/4 of their offspring would not help make the BT2 translocation and again 1/2 would have severe anamolies. Remember there is only approximatley 6.5 million years from the point we "separated" from primates.

In addition, if BT1 and BT2 were to have happened incredibly fast, so that no (or limited ie they can still mate) speciation were to have occured, the new BT1/BT2 46 chromosome primate would definitely have a child with trisomy (again invariably harmful).

More on this later... but I think this is enough.


Dave Wisker said...

I suggest you read my series of four essays on Human Chromosome 2 on the blog "The Panda's Thumb". Here is a link to the last essay, which also contains links to the previous three:

The Predestined Blog said...

Hey Dave,

Thanks for the link and comment. I will take a look at it when I have time (being in residency def. did not increase my free time...)