Penumbral Lore; the Shadows of Science

It's going to take me a little while to get back into the rhythm of writing in this blog, so forgive me if I start out a bit slowly. I was going to begin with a story about prehistoric fashion, but a search for primary sources showed that the archaeologist only published in Russian.

I found an interesting story about TB in Homo erectus, but it's either too recent to have hit the web or is available with a subscription only. Just be aware that the inference that the infected Homo erectus had dark skin is questionable.

Then there's the whole hobbit issue. Ever since they were discovered there has been debate back and forth about whether the Homo floresiensis were a race of humans or a separate species has been lobbed back and forth. A recent article in Science, "Mutations in the Pericentrin (PCNT) Gene Cause Primordial Dwarfism", with over two dozen authors, suggests that the hobbits were humans suffering from a particular form of dwarfism. Here is some criticism by blogger Greg Laden, be sure to check out the comments.

In other news - some of you may have noticed that some of my web badges have gone. I've moved them to my new craft blog Eye of the Beholder. In the I'll be adding 'yarn work' posts over there, so if that's your interest update your blog rolls...

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Blood types are a good way to begin a conversation about genetics. It's a semi-familiar topic to most of us, but not so well known that people assume they know it all going oin. It's also a fairly simple example of how things work.

The genes which code for blood type are found on Chromosome Pair #9 - the 9th longest chromosomes. It's called a pair because there are two separate chromosomes (one coming from each parent), and it's given the number 1 because it's the longest chromosome. Chromosome pair #22 is the shortest, #23 is all about sex, except when it's not (but that's another story).

The Blood type gene comes in three different sorts (called Allelles). "A" codes for antigen A. An antigen is sort of like a flavor, the bodies immune system recognizes is and either reacts against it or not. So if one or the other or both of your copies of the blood type gene are type A, your body will produce Antigen A - it only takes one copy of the gene to make the protein, even though your body has two chromosomes, each of which have the blood type gene.

"O" is any version of the blood type gene which does not code for an antigen. If both chromosomes carry the Type O gene your body does not make a blood type antigen. If one chromosome codes for Type A and the other codes for Type O your body makes antigen Type A. We say "A" is dominant over "O".

"B" is another allelle of the same gene. It codes for a different antigen than the "A" gene. If one chromosome carries "A" and the other carries "B" then both antigens are made, and the blood is Type AB. We say "A" and "B" are co-dominant, or partially dominant.

There's also a + or - factor. This is controlled by a different gene altogether, which is located on Chromosome #1 (the longest chromosome in each cell). It is inherited completely separately. If a person carries the Rh+ gene, their blood cells contain the Rh antigen (we say they are Rh positive). If their copy of the Rh gene does not code for an antigen then we say they are Rh negative.

So, the two different genes can come together in a lot of different ways. AA++, AA+-, A0--, AB--... and so on. All of these different gene combinations (genotypes) can only combine to make eight different recognizable "Blood Types" (phenotypes). O+, O-, A+, A-, B+, B-, AB+, AB-. These are the common blood types. There are other, extremely rare, blood types, but that's for a different post.

When someone donates whole blood to another person, their own immune system reacts to the antigens in the red blood cells. This is why you want to make sure that the donor and recipient have the same type of blood. If the right kind of blood isn't available, it's important to at least make sure that their blood won't trigger an immune response. Type O- blood doesn't have a "Type" antigen or an Rh antigen, and it's considered the universal donor.

If you think about platelete donation, however, the situation is reversed. The red blood cells are removed from the blood (and generally returned to the blood donor in a process called "aphereisis") so they can't trigger an immune reaction in the recipient. Blood type is still important, however, since the donors antibodies are transferred to the patient in the serum. So the universal platelete donor wouldn't have antibodies to either blood type or Rh. AB+ is the universal donor for platelets.

This afternoon I will be taking my AB+ self down to the Red Cross (opens in new window) and (if my hematocrit levels are high enough this time) donating platelets. Wish me luck!  Edit: they were, and I did.   Yay!