Genetics

A Gallifreyan has 42 chromosomes (21 pairs). Forty are autosomal, and two determine sex (XX or XY).

What really caught my attention when I did ran a karyotype was the similarity to human chromosomes. The possibility - no, likelihood - of a relationship between the species can not be denied. I include here both human and Gallifreyan karyotypes, and the karyotype of the Earth chimpanzee, the closest living relative to humans, to illustrate my suspicions.
 

Figure 1: Human Karyotype

Human physicians reading my notes will no doubt be familiar with human genetics. The Human Genome Project was after my natural time, but I have been able to access it to clarify my observations. There are 46 chromosomes, numbered by size (with the exception of 22, which is actually larger than 21) plus X and Y.

Figure 2: Chimpanzee Karyotype

Comparison of the human and chimpanzee karyotypes, to my mind, makes it impossible to deny evolution. The most significant difference is in Chromosome 2, which in all the great apes is two separate, smaller chromosomes. It is well-accepted that the combination of those two was the spark that led to the separation of the two families. Chromosomes marked * are noticeably smaller in the chimp than in the human. Arrows indicate a shift in the location of the centromere; in all cases, the chimp's centromere is closer to the center of the chromosome, and the human centromere is closer to the end. There are other differences as well, such as inversion of parts of some chromosomes around the centromere, and of course differences in the exact sequence of many genes, which are not readily visible in the karyotype.

Figure 3: Gallifreyan Karyotype

In light of what we learn by comparison of human and chimpanzee DNA, I am inclined to suggest that Gallifreyans are not only related to humans, but are in fact descended from us. This idea would not sit well with those who believe their civilization predates ours by millions of years, but as they are time travelers, they could easily have relocated themselves to give this impression. My friend never will say what year he came from.   Notice that 14 chromosomes, plus the X, are visually identical. Two appear to be combinations of ours, as our #2 is a combination of two great ape chromosomes. (See Figures 4-6) Brackets show locations in which the Gallifreyan chromosome is expanded, compared to the human. This is a matter for which I had to consult the Human Genome Project. It appears that all but two of these expansions are in locations involving hypertrophic cardiomyopathy (overgrowth of heart muscle). I strongly suspect that these genes are the ones that code for the binary cardiovascular system. Such a complex change, however, could not have occurred through natural evolution. I have a slight insight into this through stories my friend has told me. For a long time, visitors were not allowed on Gallifrey, not only to protect the Time Lords' secrets, but also for their own safety. But he brought a human woman with him once, and she fell in love with a local and demanded the right to stay. Soon after, she became gravely ill (as expected), but ultimately survived. She later became pregnant. The child's anatomy was purely Gallifreyan. I have not had the opportunity to run his karyotype, but I suspect that if I did, I would find 44 chromosomes: one copy each of 13, 14, 21, 22, and the combined 13/22 and 14/21. Whether he will be able to reproduce remains to be seen. But his mere existence is of particular note because in another case of intermarriage, which occurred on Earth, no children were possible. I am led to conclude that the binary vascular system is actually the result of a retrovirus. Other animals on Gallifrey all have it. I can only assume that the original humanoid colonists (for they must be colonists, not natural evolved there, to be related to us) were decimated by this virus, and the survivors' children developed under the new blueprint. The combining of two pairs of chromosomes could have happened naturally later on, or it could even be in the future of human evolution, prior to colonization of Gallifrey. The two remaining sites of expanded DNA are on 13/22 and the Y chromosome. Note that it is as if the human Y has been inserted at the centromere of the human X. Knowing that Gallifreyan society was at one point controlled by a female theocracy, which was overthrown by a male technocracy, I suspect that the change in the Y was engineered to protect men from the higher incidence of genetic defect due to the absence of the second X. Gallifreyan men are, by this token, essentially XXY, although they are not affected by the infertility of Kleinfelter's syndrome because the chromosomes are still in even pairs. Figure 4: Human chromosome 2 compared to chimpanzee The similarity here is not so obvious visually, because the human chromosome expanded so much. However, it is well documented in more detailed studies. Figure 5: Gallifreyan chromosome 14 compared to human (Human chromosomes cut at centromeres and combined) Unlike the chimpanzee comparison above, this is undeniable. While the specific coding of the genes may differ considerably, the chromosome as a whole is quite clearly a combination of 21 (inverted) and 14. Figure 6: Gallifreyan chromosome 13 compared to human (Human chromosomes cut at centromeres) Chromosome 22 (inverted) neatly matches the top half of Gallifreyan Chromosome 13. The match between human Chromosome 13 and the bottom half is not so clear because so much expansion has occurred. The site of expansion on 13/22 corresponds to pinealoma in humans. I will discuss the significance of this elsewhere.

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Cardiovascular  - Respiratory - Genetics - Life Cycle